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Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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B
Workshop Papers

Specifying Optimal Nutrient Composition for Military Assault Rations

Andrew J. Young, US Army Research Institute of Environmental Medicine Gerald A. Darsch, US Army Soldier Systems Center

INTRODUCTION

This report summarizes expert panel deliberations during a workshop organized by the Committee on Military Nutrition Research (CMNR) of the Food and Nutrition Board of the Institute of Medicine (IOM). The CMNR organized the workshop to address questions raised by the US Army Research Institute of Environmental Medicine (USARIEM) regarding optimal nutritional content for a new individual combat ration, First Strike Ration (FSR), being developed by Department of Defense (DoD) Combat Feeding Directorate at the US Army Natick Soldier Center. This new restricted ration was developed for highly mobile soldiers in high-intensity conflict by providing foods that can be eaten “on the move.” As a result, the FSR is smaller and lighter than the main individual operational ration, the Meal, Ready-to-Eat (MRE). In addition to their practicality, the FSR received high customer acceptance during recent deployments (Operation Enduring Freedom, Operation Iraqi Freedom). However, constraints imposed by ration design factors on the range of food components suitable for inclusion in an FSR might limit intake of certain nutrients needed to maintain soldier performance during sustained combat operations. The IOM ad hoc committee, charged with evaluating those concerns and recommending optimal nutrient content for

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

future versions of the ration, convened a workshop to gather information regarding the nutritional needs of individuals doing high-intensity activities for a short term while under stress.

OPERATIONAL RATIONS AND MILITARY OPERATIONS

US Army Field Feeding Doctrine (i.e., fundamental principles by which the military forces guide their actions) calls for supporting soldiers by providing them with “the right meal at the right place at the right time” (US Department of the Army, 1996). To accomplish this, Natick Soldier Center’s DoD Combat Feeding Directorate conducts research, development, testing, evaluation and engineering support for combat rations, field food service equipment and total combat feeding systems for the military services and the Defense Logistics Agency. To that end, the Combat Feeding Directorate has developed an appropriate range of combat rations that are available for requisition through the military supply system. Each of these rations is designed to meet the Military Reference Dietary Intakes (MDRIs) as established in AR 40-25 (US Departments of the Army, Navy, and Air Force, 2001). Detailed descriptions, including menus, nutrient content, and packaging information for the entire spectrum of these operational rations, are documented elsewhere (US Department of Defense, 2004). Table B-1 briefly summarizes key features for several of the most widely used rations.

In those instances when operational conditions preclude serving hot, cafeteria-style rations, military personnel are provided individual operational rations, of which the MRE is the flagship ration. The nutrient requirements of most deployed soldiers can be satisfied when they are provided MREs or other appropriate rations listed in Table B-1. However, due to several factors explained below, the current rations may not completely satisfy nutritional requirements of soldiers in some situations (i.e., during the assault phase of combat operations, certain Special Operations Forces missions, and missions anticipated to be conducted by Future Force Soldiers).

First, daily energy expenditures of personnel engaged in these types of military missions are so high (Tharion et al., 2005) that these soldiers will not maintain an energy balance even when they consume three complete MREs per day, which could lead to adverse physiological effects and detriments in health and performance (see also next section on “Physiological Demands of Combat Operations”). Moreover, in some cases during combat operations, soldiers receive only two MREs, which further exacerbates the situation.

Second, soldiers who must carry heavy loads or engage in strenuous military duties (e.g., light infantry, US Marine Corps, and Special Operation Forces) compound their energy balance problem by “field-stripping” the MREs. To lighten their heavy loads, soldiers often open the individual meal packages, select certain components based on individual preference, and discard the remainder.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

TABLE B-1 Principle Types of Operational Rations Fielded by the US Department of Defense

Ration

Purpose

Nutrition (Average Meal)

Key Characteristics

Unit Group Ration/Heat & Serve

Group Feeding (50 meal/module)

1,450 kcal

14% protein

32% fat

54% carbohydrate

21 menus (14 lunch/dinner, 7 breakfast)

Includes semi perishables

18 month shelf-life

113 lb, 5 ft3/module

Organized food service required

Unitized Group Ration, A

Group Feeding (50 meal/module)

1,450 kcal

14% protein

32% fat

54% carbohydrate

21 menus (same as above)

Includes perishables

3 month shelf life (made-to-order)

113 lb, 5 ft3/module

Organized food service required

Meal, Ready-to-Eat (MRE)

Individual Feeding (3 MREs/day)

1,300 kcal

13% protein

34% fat

53% carbohydrate

24 menus

Heat processed foods in flexible retort pouches

36 month shelf-life

1.5 lb, 0.052 ft3/meal

Ready-to-Eat

Meal, Cold-Weather/Food Packet, Long Range Patrol (MCW/LRP)

Individual Feeding (1 to 3 MCW/LRP per day) during cold-weather or special operation forces and marine corps

1,540 kcal

15% protein

35% fat

50% carbohydrate

12 menus

Dehydrated and dried food components, 28–40 oz water needed to fully rehydrate

36 month shelf life

1 lb/meal, 0.04 ft3/meal

Individually prepared

 

SOURCE: US Department of Defense (2004).

Because MREs and other rations were designed to meet the nutritional needs of deployed soldiers who consume the entire daily ration (in which the nutrients are not evenly distributed), such selective consumption will further decrease total intake of energy and/or will compromise adequate intake of specific nutrients. Although field-stripping does, in fact, lighten a soldier’s load, the cost of the discarded components can approach $34 over a three-day period. More importantly, studies at USARIEM and elsewhere have documented a variety of adverse biomedical and performance consequences (Lieberman, 2003; Montain and Young,

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

2003) when such semistarvation is coupled with other physiological stressors encountered during sustained combat operations (e.g., sleep deprivation, anxiety, dehydration).

The need for a specialized ration for high-tempo, assault-type missions has been recognized since the end of World War II (Samuels et al., 1947) when military planners recommended development of an “Assault Candy Ration.” To better meet the individual’s nutritional needs during these high-intensity operations, Natick Soldier Center’s Combat Feeding Directorate have developed a new smaller, lighter, individual operational ration comprised of eat-on-the-move food components, the FSR. The FSR is intended for use during specific missions such as those described above when soldiers must operate for periods of three days, or possibly longer, with minimal resupply. This ration will serve to “bridge the gap” until operational tempo abates and more nutritionally complete rations can provided. Because of the relevance of the operations for which FSRs are envisioned, their full implementation in the field may occur in an accelerated fashion; in fact, it is estimated that the FSR, pending the military services’ approval, will enter the procurement system in the first part of 2007. Through the use of spiral development generated under an Army Technology Objective (ATO) entitled “Nutritionally Optimized FSR” (IV.MD.2005.02), jointly sponsored by USARIEM and the Natick Soldier Center Combat Feeding Program, science and technology innovations are planned for insertion as part of a preplanned product improvement program. The objective of this ATO is to develop and utilize novel nutrient delivery systems, food formulations, and field feeding strategies to provide on-demand access to specific nutrients to best sustain performance. The specific strategies, when identified, will improve overall energy and nutrient intake by 20 percent and enhance cognitive and physical performance by 20 percent. The DOD asked the IOM committee to provide recommendations that will guide the design of the ration for sustained combat operations and will identify nutritional research to accomplish this objective.

WORKSHOP TASKING: RECOMMENDATIONS FOR NUTRITIONAL OPTIMIZATION OF THE FIRST-STRIKE RATION

Overall Approach

The Committee on Optimization of Nutrient Composition of Military Rations for Short-Term, High-Stress Situations asked the workshop participants to consider the specific requirements for the FSR (size, volume, weight) that constrain the ration’s design such that the ration is unlikely to provide enough energy to match the daily energy expenditures of the soldiers. Table B-2 lists important design features and performance objectives for the FSR development effort. The workshop’s primary objective was to gather information and provide recommendations regarding nutritional strategies suitable for implementation to

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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TABLE B-2 Field Feeding Approaches During Assault Phase Operations

 

Current

Future

Existing/Desired Characteristic

3 MREs/day

3 MRE’s, Field-Stripped

FSR (prototype)

FSR Goals

Size

0.25 ft3

0.16 ft3

0.13 ft3

TBD

Weight

4.75 lb

3.2 lb

2.51 lb

TBD

Nutritional Content

3,900 kcal

Unknown

2,855 kcal

TBD kcal

 

489 g carbohydrate

 

370 g carbohydrate

TBD g carbohydrate

 

132 g protein

 

101 g protein

TBD g protein

 

12 mg zinc

 

? zinc

TBD g zinc

Nutrient Delivery (% consumed)

60

Unknown

90

95

Performance

 

Unknown

 

 

Cognitive/Vigilance

Sustained

 

Sustained

Enhanced

Physical

Sustained

 

Sustained

Enhanced

NOTE: FSR = First Strike Ration; MRE = Meal, Ready-to-Eat; TBD = to be determined.

make an FSR that would best sustain health and performance despite semistarvation arising from high daily energy expenditure and constrained energy intake. Box B-1 details several specific questions that the workshop was directed to address. The overall question was the following: Given the fact that weight and size limitations preclude the FSR from completely preventing negative energy balance in soldiers subsisting on the ration, would health and performance best be preserved by a nutrient composition that maximizes energy density (i.e., minimize energy deficit) or, alternatively, by a micro- and macronutrient composition that specifically optimizes health status and performance, potentially at the expense of a less than maximum energy density?

Besides addressing nutrient content, the speakers at the workshop were also asked to consider ration design approaches to enhance overall consumption of the ration. The problem of ration underconsumption during field training and operational deployments is well documented and was the focus of an earlier report (IOM, 1995). The CMNR previously concluded that five broad categories of factors contributed to ration under consumption.

The first four categories of factors related to the environment and to behavior that potentially impairs appetite and/or limits food consumption were identified as the following: exposure to harsh climate and danger (environment); social interactions during meals; appropriateness of the meal to time of day (eating situation); and the attitudes toward field-feeding systems held by soldiers and

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

BOX B-1
Questions to Be Addressed by CMNR Workshop on Optimization of Nutrient Composition of Military Rations for Short-Term, High-Stress Situations

  1. Should energy content (energy density) of the First Strike Ration (FSR) be maximized so as to minimize the energy debt, or is there a more optimal “mix” of macronutrients and micronutrients, not necessarily producing maximal energy density?

  2. What is the optimal macronutrient distribution (protein, fat, and carbohydrate) for the FSR to best sustain and/or enhance performance during combat missions?

  3. What are the specific types and amounts of macronutrients (e.g., complex verses simple carbohydrates, proteins with specific amino acid profiles, type of fat, etc) to optimize such FSR to enhance performance during combat missions?

  4. What are the specific types and levels of micronutrients (antioxidants, cofactors, vitamins, minerals, pre- and probiotics or other bioactives that could/should be added to the FSR to enhance performance during combat missions?

  5. What strategies (passive or active) could increase FSR consumption and enhance nutritional status of soldiers conducting combat operations? Consideration should include but not be restricted to:

    1. Component packaging, types, sizing, flavors

    2. Bioavailability factors

  1. Recommendations must be feasible, practical, and physiologically meaningful.

their leaders (individual). Based on the CMNR recommendations, technical reports and commanders’ guides have been prepared and distributed providing guidance to minimize the effect of those negative factors; however, from a practical standpoint, commanders conducting combat operations are permitted little flexibility to mitigate those kinds of stressors. The fifth category is underconsumption factors, related to a ration’s characteristics that influence customer acceptability and for which the committee offered more practical recommendations to improve consumption. These recommendations included the following: to enhance menu variety; to improve food sensory features, packaging, and ease of use for the rations and components; and to provide smaller snacking or “nibbling” food items as well as energy- and nutrient-rich beverages that could be carried in pockets and consumed quickly while on the move.

Clearly, those recommendations should be the driving focus behind the FSR. All of those approaches have already been incorporated into the newest versions of the MRE and other operational rations during the continuous product improvement programs that Combat Feeding Directorate conducts and they have been recognized by troops who consume combat rations. For this workshop, the panel

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

of experts was asked to consider how similar, practical approaches could be used to further enhance consumption of the FSR, thereby better satisfying the nutritional needs of soldiers during assault type operations.

Workshop Overview

Under the auspices of the CMNR, the Committee on Optimization of Nutrient Composition of Military Rations for Short-Term, High-Stress Situations and the IOM organized a workshop to address the questions posed by USARIEM. The workshop was hosted by USARIEM and the Natick Soldier Center in Natick, MA, in August 2004. USARIEM scientists provided the workshop participants with their tasks, overviews of military ration systems, and background briefings on the physiological and medical consequences of combat operations on military personnel. For the remainder of the workshop, invited scientific experts presented information on topics organized into five major categories: optimization of macronutrient composition; optimization of micronutrients and other bioactive compounds; nutritional optimization of the immune system; nutritional preventive medicine; and food product development. Those presentations are the basis for the remainder of this report.

REFERENCES

IOM (Institute of Medicine). 1995. Not Eating Enough. Washington, DC: National Academy Press.


Lieberman HR. 2003. Nutrition, brain function and cognitive performance. Appetite 40(3):245–254.


Montain SJ, Young AJ. 2003. Diet and physical performance. Appetite 40(3):255–267.


Samuels JP, McDevitt RP, Bollman MC, Maclinn W, Richardson LM, Voss LG. Conway HA. 1947. In: Meyer AI, eds. Ration Development. Operational Studies 1(12). Fort Lee, VA: Office of the Quartermaster General.


Tharion WJ, Lieberman HR, Montain SJ, Young AJ, Baker-Fulco CJ, Delany JP, Hoyt RW. 2005. Energy requirements of military personnel. Appetite 44(1):47–65.


US Department of the Army. 1996. Basic Doctrine for Army Field Feeding and Class 1 Operations Management. FM 10-23. Washington, DC: Department of the Army.

US Department of Defense. 2004. Operational Rations of the Department of Defense. Natick PAM 30-25. Natick, MA: US Army Natick Soldier Center.

US Departments of Army, Navy, and Air Force. 2001. Nutrition Standards and Education. AR 40-25/BUMEDINST 10110.6/AFI 44-141. Washington, DC: US Department of Defense Headquarters.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

Physiological Demands of Combat Operations

Scott J. Montain, US Army Research Institute of Environmental Medicine

INTRODUCTION

The combat foot soldiers within the light infantry and special operations units are the military populations targeted for use of next-generation assault rations. These soldiers are required to carry or transport all of the supplies, sometimes exceeding 50 kg, they will need for the operation. Missions often are of the continuous type termed “sustained operations” (SUSOPS) lasting from two to seven days or longer that consist of near-continuous physical work, restricted sleep, and limited breaks for meals. While the energy cost of any single task is not necessarily high, total daily energy expenditures can reach extremely high levels because of long hours of wakefulness. Thus, these soldiers are faced with sustained environmental exposure, exertional fatigue, sleep deprivation, and energy deficits.

The lightweight and small assault ration being developed specifically for these soldiers must be capable of sustaining their performance while in repeated SUSOPS missions lasting for three days when energy expenditures exceed 18 MJ (4,300 kcal)/day, and up to seven days during which daily energy expenditures are expected to be less. This chapter describes the physiological challenges facing combat foot soldiers to facilitate defining their nutritional requirements. This topic has been discussed in greater depth in other publications (Friedl, 2003; Tharion et al., 2005), and the reader is referred to these papers for additional information.

ENERGY COST OF SOLDIER ACTIVITIES

The total daily energy expenditures of combat units during training exercises has ranged from 15.5 to 29.8 MJ (3,700 to 7,120 kcal)/day (Figure B-1); with the highest values occurring during cold-weather operations. The tasks performed typically have included long, sustained periods of low to moderate intensity work (expected metabolic rates of 250 to 450 Watts), with short periods of relatively high-intensity work (expected metabolic rates in excess of 600 Watts). Factors contributing to these high daily energy expenditures have been the relatively long periods of work (> 15 h/day), traversing rough terrain or soft surfaces (e.g., snow, mud, or sand), and carrying heavy loads.

Much of what we know regarding the energy cost of soldier activities comes from investigations of soldiers performing simulated combat missions as part of training courses. In these scenarios, total daily energy expenditures (TDEE) are often quite high. For example, airmen participating in the US Air Force Combat Survival Course averaged 19.7 MJ (4,700 kcal)/day of TDEE (Jones et al., 1992),

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

FIGURE B-1 Measured troop energy expenditures during military field operations.

NOTE: TEE = total energy expenditure.

SOURCE: Tharion et al. (2005).

soldiers attending the US Army Special Forces Assessment School averaged 21.7 MJ (5,180 kcal)/day (Fairbrother et al., 1995), and marines at the US Marine Corps Infantry Officer Course averaged 22.5 MJ (4,700 kcal)/day of TDEE during cold-weather operations (Hoyt et al., 2001) and 16 to17 MJ (3,820 to 4,060 kcal)/day during hot weather (author’s unpublished results; personal communication, R. Hoyt, US Army Research Institute of Environmental Medicine, 1999). The US Air Force Combat Survival Course is a 5-day course that trains aircrew members in parachuting and survival, evasion, resistance, and escape procedures, as well as simulated prisoner of war interrogations. The US Army Special Forces Assessment School conducts 20-day training and includes activities such as physical fitness tests, battle marches, and long-range movements carrying backpacks, weapons, and other field equipment. In the Marine Corps Infantry Officer Course, marines perform a series of simulated combat operations using dismounted infantry, mounted infantry, and amphibious tactics. In each of these courses, night operations are included, leading to near-continuous physical work, with marines active 16 to 22 h/day.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

Students enrolled in the US Army Ranger training course perform a series of physically demanding field exercises intermittently over a 60-day period. While total energy expenditures averaged over the 60-day course are lower than those for many of the shorter, more intense military training courses, they are still quite high, averaging 16.8 MJ (4,010 kcal)/day (Moore et al., 1992) and 17.1 MJ (4,090 kal)/day (Shippee et al., 1994) for more than two months. Combat fundamentals taught during the course include patrolling; squad reconnaissance and ambush; mountaineering; small boat operations; and attack, ambush, and raid drills. The unique aspect of this course is repeated, periodic food restriction and sleep deprivation as one of the intentional stressors—making it a model for studying the physiological strain likely to be imposed on soldiers performing repeated SUSOPS missions during combat, which is the subject of interest in this workshop.

As noted in the introduction, combat foot soldiers carry their own supplies at high energy expenditure costs. The loads they carry can be very heavy depending on what phase of a mission they are performing. A recent study (Dean and Dupont, 2003) in which soldier loads were measured during actual operations in Afghanistan revealed that soldiers in the traveling phase of a mission carried an average of 59.3 kg (131 lb). Their approach load averaged 45.7 kg (101 lb), and their fighting load averaged 28.5 kg (63 lb). When normalized to body weight, these loads were equivalent to carrying 77 percent, 57 percent, and 35 percent of body mass, respectively. Current soldier development efforts are exploring methods to dramatically lower the soldier load, but soldier load remains a major physical stressor during combat execution.

PHYSIOLOGICAL CONSEQUENCES OF COMBAT OPERATIONS

The massive load each soldier carries limits the amount of space and weight that soldiers are willing to reserve for food. The nature of SUSOPS missions also means that food is consumed on the go. These two factors lead to soldiers stripping their personal rations of items that they don’t like or will be unlikely to eat. When voluntary intake has been measured, it typically averages between 10 and 12 MJ (2,390 to 2,870 kcal) (Baker-Fulco, 1995). Since energy expenditure is often much higher than intake, there is demand placed on endogenous energy stores to meet energy demands of the mission.

Metabolic Status and Body Composition Changes

Blood glucose levels typically decrease over SUSOPS missions, but the average values generally only fall 10 mg/dL (0.5 to 0.6 mM) from baseline values. There are soldiers, however, who demonstrate much higher reductions. In a recent investigation (author’s unpublished results), during which marines consumed 1,600 kcal/day and 210 g of carbohydrate/day while expending

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

3,850 kcal/day, it was observed that 12 to 23 percent of volunteers had blood glucose values below 76 mg/dL (< 4.2 mM) after four to eight days of SUSOPS. Concomitant with these metabolic changes were substantial increases in blood ketone and free fatty acid concentrations.

The underfeeding accompanying SUSOPS is accompanied by reductions of both fat and lean body mass. For example, Nindl and colleagues (2002) reported fat and lean tissues losses of 1.2 and 1.5 kg, respectively, over a 72 h SUSOPS. Similarly, Moore and colleagues (1992) reported that 38 percent of the 12 kg body mass loss that occurred during Ranger training (when severely underfed) was attributable to nonfat tissue loss.

Cognitive Performance

Opstad and colleagues (1978) found that visual vigilance decreased 4 to 28 percent after three to four days of sustained operations activity. Reaction time and coding declined 12 to 30 percent over the same time period, while prone marksmanship declined 10 percent. Inclusion of three to six hours of continuous sleep once during the five-day operation partially or fully reversed these declines. There was large interindividual variability, but general deterioration occurred due to omissions, not mistakes. Similar results have been reported by others, as Bugge and colleagues (1979) observed, decreased logical reasoning (46 percent), letter cancellation attempts (40 percent), and code test scores (45 percent) after four days of sustained operations. More recently, Tharion and colleagues (1997) reported a reduction in visual vigilance (44 percent), slower processing (21 percent), and fewer correct responses (17 percent) on a four-choice reaction test, and compromised performance on a match to sample task after 73 to 74 h of sleep deprivation and operational stress. Associated with the impaired cognitive performance were increased levels of fatigue, confusion, tension, and depression. Shippee and colleagues (1994) evaluated decoding, memory, reasoning, and pattern recognition during the eight-week US Army Ranger Course. Soldiers maintained near perfect accuracy at decoding and reasoning at the expense of speed (7 to 10 percent fewer attempts). Memory accuracy declined over time. Both speed and accuracy were impaired on the pattern recognition task—particularly during the desert and jungle phases.

Physical Performance

Prolonged operations lasting several weeks’ duration and associated with substantial losses of lean body mass (Moore et al., 1992; Shippee et al., 1994) have resulted in reductions (20 percent) in maximal lifting capacity and vertical jump height (15 to 16 percent). Shorter duration studies with minimal lean body mass loss generally showed little or no decrement in muscle strength, power, or fatigability (Bulbulian et al., 1996; Guezennec et al., 1994; Vanhelder and

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

Radomski, 1989); however, this is not universal (Legg and Patton, 1987). Sustained operations scenarios lasting less than one week have resulted in reduced maximal aerobic power and endurance (Guezennec et al., 1994) as have sleep-deprivation studies (Vanhelder and Radomski, 1989).

Performance of simple and well-learned motor tasks (e.g., weapon handling) do not appear to be compromised by sustained operational stress (Haslam, 1984). However, endurance time is frequently impaired during aerobic exercise tasks (Vanhelder and Radomski, 1989), and there is an increased perception of effort to perform the same task. Nindl and colleagues (2002) recently reported 25 percent lower work productivity on a physical persistence task; in agreement with the hypothesis that SUSOPS compromises prolonged and monotonous tasks (Figure B-2). Independent of energy intake (Rognum et al., 1986), operational effectiveness is also affected if sleep is inadequate.

Marksmanship can be compromised by sustained operation activities particularly when very little restorative sleep is obtained. Tharion and colleagues

FIGURE B-2 Work productivity on a physical persistence task over 72 h of simulated military sustained operations (SUSOPS) training as well as a control week without near-continuous work and underfeeding.

SOURCE: Nindl et al. (2002).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

(2003) reported significantly impaired marksmanship after 73 to 74 hours of total sleep deprivation during Navy Seal training. Specifically, they observed greater distance from center of mass (38 percent) increased dispersion of shot groups (235 percent), as well more missed targets (37 percent), all indicative of reduced marksmanship. These adverse findings occurred despite a 53 percent slower sighting time. In contrast, Johnson and colleagues (2001) reported that despite soldiers rating the marksmanship task as more difficult to perform after 48 and 72 h of SUSOPS (2 h of sleep per night), there was no reduction in the number of randomly appearing targets hit during the test. Haslam (1984) reported no negative results during nine days of sustained operations and sleeping either 1.5 or 3 h daily on shot group clustering when troops fired in the prone supported position. However, their ability to acquire and accurately hit a randomly appearing target declined during the course. The group receiving only 1.5 h of daily sleep performed 50 percent below baseline from days 5–9 of the field exercise, whereas the group receiving 3 h of daily sleep had a more modest reduction (the number of hits fell from 6–7 to 4–5).

Similarly, the caloric deficit associated with sustained operations scenarios appears to have inconsistent effects on soldier performance (Montain and Young, 2003). Rognum and colleagues (1986) reported no difference either in time to complete an assault course or in prone marksmanship performance when students were provided 1,500 or 8,000 kcal/day during a five-day scenario. However, Guezennec and colleagues (1994) observed 8 percent reductions in maximal aerobic power when soldiers were restricted to 1,800 kcal/day but no reduction in maximal aerobic power when soldiers were fed 3,200 or 4,200 kcal/day. Similarly, Tharion and Moore (1993) reported reductions in shot group tightness on a marksmanship task after sustained road marching soldiers were fed 250 g of carbohydrate per day, but no change when soldiers consumed a diet with 400 or 550 g of carbohydrate.

Time and content of the previous meal may be an explanation for the divergent results. Montain and colleagues (1997) reported a relationship in that an increase in energy (or carbohydrate) intake sustains uphill run time over three days of physically demanding field training. Moreover, 11 of 13 soldiers who best sustained uphill-run performance had eaten 70 to 378 g of carbohydrate during the four h preceding the uphill run, while 10 of the 13 soldiers with the greatest decrement had eaten none of their rations since the previous night’s meal. All participants in this study were provided with two Meals, Ready-to-Eat each day or approximately 2,600 kcal and 300 g of carbohydrate per day. These data suggest that soldiers subsisting on diets with these energy and carbohydrate levels during high-tempo operations are receiving near the minimum energy necessary to sustain performance, necessitating good food discipline (i.e., eating the food provided), and good food choices (i.e., eat the carbohydrate-containing foods) to preserve physical performance.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×
Endocrine Changes

Dramatic changes in the blood hormonal milieu arise during sustained operations protocols and persist during both rest and exercise. In the five day Norwegian Ranger Course, in which food and sleep are kept to a minimum, there was a progressive increase in catecholamine concentration (Rognum et al., 1981) as well as cortisol, growth hormone, and aldosterone levels (Opstad, 1992; Opstad and Aakvaag, 1981) and a reciprocal fall in testosterone and prolactin (Opstad and Aakvaag, 1982) as well as other adrenal and testicular androgens (Opstad, 1992). The increase in catecholamine concentration is associated with a downregulation of adrenergic receptors on white blood cells (Opstad et al., 1994). Similar observations have been reported for soldiers participating in the US Army Ranger Selection Course (Moore et al., 1992; Shippee et al., 1994).

The decline in testosterone (up to 70 percent from baseline) and other anabolic hormones may be due in part to the caloric and/or protein restriction imposed during the courses. Short periods of refeeding quickly reverse declines in insulin-like growth factor-1 (IGF-1) (Friedl et al., 2000) (Figure B-3). When additional energy of a mixed diet of protein, fat, and carbohydrate have been provided (400 and 1,400 kcal), reductions in IGF-1 and testosterone were attenuated (Friedl et al., 2000; Guezennec et al., 1994). However, when additional calories (4,900 kcal) have been provided predominately by carbohydrate alone, testosterone reductions were only modestly lowered (Opstad and Aakvaag, 1982), suggesting that the testosterone and IGF-1 changes may have been consequent to energy deficit and possibly insufficient amino acid intake (Sanchez-Gomez et al., 1999).

Immune Function

The effects of sustained operations on immune function remain poorly understood. The outbreak of infectious disease among soldiers participating in US Army Ranger and Special Forces Assessment Schools suggests that multistress environments can compromise immune defense mechanisms (Moore et al., 1992). Changes in immune cell parameters and in vitro responses to stress have varied from study to study, but they appear related to the duration and severity of the sustained operations stress.

The five day Norwegian Ranger Course produced a general leukocytosis, predominantly due to two- to threefold increase in neutrophils and monocytes (Boyum et al., 1996). Lymphocyte numbers decreased as did CD4 T cells, CD8 T cells, CD16 natural killer cells, and CD19 B cells. Neutrophil chemotaxis and oxidative burst capacity increased during the course before returning to baseline levels (or below) after five days of training (Wiik et al., 1996). These changes have been attributed to sleep deprivation and appear relatively insensitive to changes in caloric (carbohydrate) intake (Wiik et al., 1996). Immunoglobulin M

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

FIGURE B-3 Insulin-like growth factor-1 (IGF-1) response to US Army Ranger Training under two levels of underfeeding and response to several days of refeeding during the course. Letters indicate means that are not significantly different (Scheffe’s test).

NOTE: Different letters indicate a significant difference in IGF-1 response (e.g., a versus b).

SOURCE: Friedl et al. (2000).

and immunoglobulin A decrease 20 to 30 percent during the course, while mitogenic responses to antigen exposure have not been consistent from course to course (Boyum et al., 1996).

The activities of the eight week US Army Ranger School appear to modify immune function, although the magnitude varies among the type of response. For example, Moore and colleagues (1992) found a similar percentage of positive delayed hypersensitivity responses to streptococcus and tetanus over the course despite relatively severe sleep deprivation and a 16 percent drop in body mass. There was no change in immunoglobulin concentrations during the course. However, as lymphocyte proliferation to mitogen stimulation declined during the course, an increasing number of students became pneumonia carriers, and 25 percent of the students sought medical attention for infections during the final portion of the course (swamp and desert phases).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

Additional ranger studies (Bernton et al., 1995) revealed reductions in cell mediated immunity responses among the trainees. Shippee and colleagues (1994) examined immunological responses after students were provided additional calories during the course. Only 2 to 8 percent of the students required medical attention during the mountain and swamp phases. Immunoglobulin levels did not change, and neutrophil oxidative burst capability increased during the course. There was a general leukocytosis, due primarily to increased granulocytes, but lymphocyte concentrations fell. The ability of leukocytes to proliferate in response to mitogen stimulation was suppressed but was less than reported in previous courses when underfeeding was more severe (Moore et al., 1992). These latter responses suggest a possible shift in proportion of lymphocytes of the T-helper type 1 (TH1) phenotype (cell-mediated) to the T-helper type 2 (TH2) phenotype (antibody-mediated). This immune system adaptation occurs after trauma (Decker et al., 1996; Mack et al., 1997; O’Sullivan et al., 1995) and with disease (Raziuddin et al., 1998) and can immunocompromise the host to certain types of infectious agents (Mack et al., 1997; O’Sullivan et al., 1995).

SUMMARY

The goal of the US military developmental assault ration, currently called the First Strike Ration, is to sustain troop health and performance for at least 96 h of unsupported military operations. To accomplish this objective, the nutritional components must sustain a soldier commonly expending in excess of 18 MJ (4,300 kcal) of energy per day and carrying loads in excess of 45 to 50 kg during while exposed to environmental extremes. It is well documented that the mission stress can challenge immune and neuroendocrine homeostasis and if sutained too long or repeated too frequently, that troop health and performance can be compromised. Likewise, there is evidence that nutritional support can reduce the physiological strain. The challenge is in defining the proper mix of macro- and micro-nutrients to sustain the soldier within a ration system the soldiers will choose to carry and consume during mission execution.

ACKNOWLEDGMENTS

The views, opinions and/or findings in this report are those of the authors, and should not be construed as an official Department of the Army position, policy, or decision, unless so designated by other official documentation.

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Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Shippee R, Friedl K, Kramer T, Mays M, Popp K, Askew E, Fairbrother B, Hoyt R, Vogel J, Marchitelli L, Frykman P, Martinez-Lopez L, Bernton E, Kramer M, Tulley R, Rood J, Delany J, Jezior D, Arsenault J. 1994. Nutritional and Immunological Assessment of Ranger Students with Increased Caloric Intake. Technical Report No. T95-5. Fort Detrick, MD: US Army Medical Research and Materiel Command.


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Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Tharion WJ, Shukitt-Hale B, Lieberman HR. 2003. Caffeine effects on marksmanship during high-stress military training with 72 hour sleep deprivation. Aviat Space Environ Med 74(4):309–314.


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Carbohydrate and Fat Intake: What is the Optimal Balance?

Jørn Wulff Helge, Copenhagen Muscle Research Center

INTRODUCTION

This paper addresses the optimal distribution of fat and carbohydrate to be included in the macronutrient composition of military assault rations as well as the specific types of fat to be used in these rations, and describes possible related performance and health issues. The purpose of this paper is to provide guidance regarding questions that may be used to make recommendations for an optimal ration composition, the task of the Committee on Optimization of Nutrient Composition of Military Rations for Short-Term, High-Stress Situations. To provide practical guidance for the complex and broad issues when improving fat and carbohydrate composition of assault rations, this paper focuses on these specific questions:

What is the optimal fat–carbohydrate balance in the ration?

  • Is it possible to perform strenuous physical tasks/training on a high-fat diet?

  • Is there a performance enhancement under short-term exposure to a fat-rich diet?

  • What do we know about the effects of energy deficit and heavy physical demand on the carbohydrate/fat balance–substrate stores?

Are there specific types of fat that are optimal for the ration?

  • Do specific fatty acids affect performance?

  • Do specific fatty acids affect health issues?

These questions are addressed using the assumptions specified for the military assault situation: The ration is targeted for well-trained male soldiers, with an average weight of 80 kg, undergoing average daily energy expenditures of

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

4,000 to 4,500 kcal, and deployed to repeatable three- to seven-day missions with recovery periods of one to three days. During these missions, they are carrying a heavy load while engaged in prolonged, low- to moderate-intensity activity (up to 20 h/day) interspersed with brief, high-intensity activity.

OPTIMAL FAT–CARBOHYDRATE BALANCE IN THE RATION

Strenuous Physical Tasks and Training on a High-Fat Diet

It is well known that work performed at higher exercise intensities requires a large contribution of carbohydrates (Brooks and Mercier, 1994). Furthermore, there is evidence that short-term, high-fat diet adaptation can be used to spare muscle glycogen and decrease carbohydrate oxidation during exercise and, hypothetically, increase high-intensity exercise capacity (Burke and Hawley, 2002; Helge, 2000). Unfortunately, such carbohydrate sparing after short-term, high-fat diet adaptation is often accompanied by a reduced muscle (Phinney et al., 1983) and liver (Hultman and Nilsson, 1971) glycogen storage in comparison with the results from consumption of a short-term, high-carbohydrate diet. It is, therefore, pertinent to know whether high-intensity exercise capacity can be upheld when dietary fat contribution is high.

Stepto and colleagues (2002) studied seven elite trained endurance athletes who underwent two four-day dietary periods consuming either a high-carbohydrate diet (70 to 75 percent carbohydrate) or a high-fat diet (> 65 percent fat) in a crossover design with an 18-day washout period in between. During the dietary adaptation period, subjects performed two controlled exercise sessions on days one and four, during which they exercised for 20 minutes at 65 percent of VO2max and subsequently performed eight 5-minute exercise bouts at 86 percent of VO2max interspersed with 60-second breaks. In addition to the training performed in the laboratory, the subjects also undertook training outside, but no difference in duration of training was apparent between dietary adaptation periods. The subjects were capable of performing the training, except during one high-intensity exercise bout, while consuming the fat-rich diet. Despite these results, the subjective rating of perceived exertion was higher on day four in the last few bouts after a fat-rich diet when compared with the results of a carbohydrate-rich diet (Table B-3). These results indicate that, for at least four days, elite athletes are capable of performing training at a reasonably high intensity while consuming a fat-rich diet but with a higher subjective rate of perceived exertion.

Consistent with these data, we noted that in our studies involving moderately untrained male subjects during long-term training and high-fat diet adaptation, the subjects on a high-fat diet were able to train and exercise at moderate and high intensities but perceived increased mental effort as compared with subjects on a high-carbohydrate diet (Helge, 2002). There is currently no explanation for this higher mental effort, but previous studies of subjects on a short-

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

TABLE B-3 Comparing the Effects of a High-Carbohydrate Diet versus a High-Fat Diet on Elite Trained Athletes

Day 4

High-Carbohydrate Diet

High-Fat Diet

VO2 (L/minute)

Bout 1

4.3 ± 0.4

4.3 ± 0.4

Bout 4

4.3 ± 0.4

4.4 ± 0.3

Bout 8

4.3 ± 0.3

4.5 ± 0.2

RER

Bout 1

0.94 ± 0.03

0.86 ± 0.03

Bout 4

0.91 ± 0.03a

0.85 ± 0.03

Bout 8

0.90 ± 0.04a

0.85 ± 0.02

RPE

13.8 ± 1.8

16.00 ± 1.3a

NOTE: Values are mean ± standard error of the means. RER = respiratory exchange ratio; RPE = rate of perceived exertion; VO2 = oxygen uptake during exercise at 80 percent of peak power output (86 percent VO2max).

a(p < 0.05) high carbohydrate versus high fat.

SOURCE: Stepto et al. (2002).

term adaptation to a fat-rich diet (Galbo et al., 1979; Jansson et al., 1982) found a higher catecholamine response and heart rate during submaximal exercise as compared with subjects on a carbohydrate-rich diet. The possible influence of a high-fat diet adaptation on the sympathetic nervous system response during exercise might cause mental strain; however, the mechanistic coupling between the increase in sympathetic response induced by a high-fat diet and the increased perception of exertion during submaximal exercise remains to be explained.

Effects of Short-Term Consumption of a Fat-Rich Diet on Performance

The coupling between muscle glycogen storage and endurance exercise capacity, which was demonstrated by Bergstrom and colleagues (1967), spurred researchers to investigate means to manipulate glycogen storage and use or both. One approach was a fat-rich diet adaptation, which induces markedly higher fat oxidation during exercise and reduced carbohydrate use (Christensen and Hansen, 1939; Phinney et al., 1983). This higher fat oxidation, however, occurs at the expense of a muscle glycogen concentration that is, at best, maintained and, in many cases, lower than that in those consuming a carbohydrate-rich diet (Helge et al., 1998b; Phinney et al., 1983). Despite these conflicting adaptations, a number of studies have manipulated the dietary fat content to achieve an improved performance capacity. In this context, short-term exposure to fat-rich diets is defined as adaptation periods lasting less than eight days and having a fat content contributing more than 40 percent of total energy in the diet. The studies are

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

listed in Table B-4, and overall, only one study shows an increased capacity to perform exercise after short exposure to a fat-rich diet. This study, by Muoio and colleagues (1994), has been extensively criticized in the literature due to a nonrandomized use of diet adaptation. The remaining ten studies found either an unchanged (three studies) or decreased (seven studies) exercise capacity after a short-term, fat-rich diet, indicating a lack of performance enhancement after such consumption and, in the worst case, a decreased performance. However, because of the number of variables influencing these findings (such as the content of fat:carbohydrate in the diet, the subjects’ training background, the exercise intensity, and the type of exercise test applied to test performance enhancement [Helge et al., 1998b]), caution should be used when drawing final conclusions. A more detailed discussion on the effects of short-term, high-fat adaptation can be found elsewhere (Burke and Hawley, 2002; Helge, 2000).

Effects of Energy Deficit and Intense Physical Activity on the Carbohydrate–Fat Balance and Substrate Stores

An essential goal for the assault ration is to enable soldiers to perform prolonged, low-intensity activity interspersed with high-intensity activity, with a daily energy deficit estimated to be approximately 2,000 kcal.

Only few studies are available in which the conditions mimicked those experienced by the soldiers. At the Copenhagen Muscle Research Centre, we have studied two groups of moderately to well-trained men who, fully self-supported and on cross-country skis pulling heavy sledges, traversed the Greenland ice cap (Helge et al., 2003; unpublished results). The dietary macronutrient compositions and basic subject characteristics are given in Table B-5. The two groups crossed the ice cap in 42 and 32 days and experienced a weight loss of approximately 6 and 7 kg, respectively, of which the majority was fat and the remainder, lean body mass (Figure B-4). Based on standard calculations, these losses are equivalent to a daily energy deficit of approximately 1,000 to 1,500 kcal. Albeit the differences in study design (e.g., the two interventions are for longer terms than those for the assault rations), the results may provide useful information for developing assault rations. The skiers’ maximal oxygen uptake remained unchanged in upper-body exercise (arm cranking), but it decreased in lower-body exercise (normal bicycle) (Helge et al., 2003; unpublished results). Accordingly, the muscle biopsy data, enzyme activities, and capillarization data indicated that the arm muscle response tended to be positive, whereas the leg muscle response was neutral or negative. Overall, this would suggest that despite the energy deficit and the type and large amount of physical work, the macronutrient compositions did provide sufficient substrate to almost fully fuel and retain the capacity for physical activity. Based on the available evidence, the fat content could probably be increased up to 50 percent without causing adverse effects. Unfortunately, due to the study design and the timing of muscle biopsies,

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

TABLE B-4 Short-Term Adaptation for High-Fat Diets and High-Carbohydrate Diets in Humans: Effects on Endurance Performance

 

Duration (days)

Dietary Content

Exercise Intensity

Fat (% of energy)

Carbohydrate (% of energy)

% of VO2max

Performance Reference measure (min)

Christensen and Hansen, 1939

3

94

4

176 Watta

88 ± 4

3

3

83

176 Watt

240 (n = 2)

Bergstrom et al., 1967

3

46

5

75

57 ± 2*

3

0

82

75

167 ± 18*

Martin et al., 1978

3

< 10

72

33 ± 3

3

> 75

72

78 ± 5*

Galbo et al., 1979

4

76

10, 5

70

64 ± 6

4

76

10, 5

70

59 ± 6

4

9, 5

77

68

106 ± 5*

O’Keeffee et al., 1989

7

59

13

80

60 ± 5

7

72

80

113 ± 12*

Williams et al., 1992

7

48

37

71

135 ± 5

7

35

56

71

127 ± 5

Muoio et al., 1994

7

38

50

75–80

91 ± 10*

7

24

61

75–80

69 ± 7

7

15

73

75–80

76 ± 8

Starling et al., 1997

1

68

16

75b

139 ± 7

1

5

83

75

117 ± 3*

Pitsiladis and Maughan, 1999

3

65

9

70 (10°C)c

89.2 [78–130]d

3

9

82

70 (10°C)

158 [117–166]*

3

65

9

70 (10°C)

44 [32–51]

3

6

82

70 (10°C)

53 [50–82] *

Burke et al., 2000

5 + 1e

68

19

TTf

31 ± 1

5 + 1

13

74

TT

34 ± 3

Carey et al., 2001

6 + 1e

69

16

TTg

44 ± 1 km

6 + 1

15

70

TT

42 ± 1 km

NOTE: Data are mean values; however, for exercise performance mean ± standard error of the means; n = number in sample.

*p < 0.05 different from other diets (same exercise intensity).

†Performance measure is time (min) to exhaustion unless otherwise noted.

‡Performance mesure is time (min) to complete task.

aExercise performance at 1,080 kJ (VO2 during exercise was 2.6 L).

bPerformance was measured as a 1,600 kJ, self-paced cycling bout.

cRoom temperature.

dMean and range.

eHigh-fat diet followed by one day of high-carbohydrate diet.

fTime trial (TT) (7 kJ/kg body mass).

gTime trial (TT) (60 min).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

TABLE B-5 Subject Characteristics and Dietary Composition

Study

Study 1

Study 2

Subject Number

4

7

BMI

26 ± 0.6

26 ± 0.7

Crossing time (days)

42

32

Exercise per day (hours)

5–6

5.5

Energy intake (kcal)

4,500 ± 300

4,300 ± 200

Fat (% of energy)

31 ± 1

39 ± 1

Protein (% of energy)

9 ± 1

11 ± 1

Carbohydrate (% of energy)

60 ± 1

50 ± 1

NOTE: Values are mean ± standard error of the means; BMI = body mass index.

SOURCE: Author’s unpublished results.

muscle substrates during the traverse are unavailable. Of particular interest in this context, however, is whether the muscle triacylglycerol stores, a main substrate source during prolonged, low- to moderate-intensity exercise in well-trained soldiers, are replenished by the ration. Several research groups recently have suggested that repletion of muscle triacylglycerol stores after physical activity could be important to optimize muscle recovery and exercise capacity (Berggren et al., 2004; Johnson et al., 2004; Spriet and Gibala, 2004). Decombaz and colleagues (2001) suggested that daily consumption of fat at a level of 2 g/kg of body mass would be sufficient to fully restore muscle triacylglycerol levels. This would imply that an average soldier at 80 kg would need to consume fat at a level of 160 g/day, which is achieved if the ration contains approximately 55 percent of total energy as fat. The macronutrient composition in the ration must be optimized such that the replenishment of both muscle glycogen and triacylglycerol is sufficiently increased within the given energy limitation of the ration.

SPECIFIC FATS FOR THE ASSAULT RATION

Fatty Acids and Optimal Performance

In the literature, animal studies have demonstrated preferential mobilization (Raclot and Groscolas, 1993) and oxidation (Jones et al., 1992; Leyton et al., 1987; Shimomura et al., 1990) of unsaturated versus saturated fatty acids. As mentioned, interventions that spare carbohydrate use may benefit performance capacity. The available evidence showing that a difference in dietary fatty acid composition will affect endurance is, however, sparse. In rats, endurance performance, measured in vitro in rat extensor digitorum longus muscle after intermit-

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

FIGURE B-4 Mean and individual changes in body composition in (A) four male subjects (data from Helge et al., 2003) and (B) seven male subjects (authors unpublished results) after crossing the Greenland ice cap on cross-country skis in 42 (A) and 32 (B) days.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

tent, low-frequency stimulation, was lower after nine weeks’ adaptation to a diet rich in n-6 fatty acids as compared with adaption to a diet rich in n-3 fatty acids; both diets contained 10 percent fat (w/w) (Ayre and Hulbert, 1996). Another study in rats found no effect of dietary fatty acid composition on endurance performance in trained or sedentary animals after high-fat diet adaptation, but substrate oxidation was affected (higher oxidation) by the dietary fatty acid composition (Helge et al., 1998a, see Figure B-5). Studies in salmon (McKenzie et al., 1998; Wagner et al., 2004) have also addressed the effects of dietary fatty acid composition on performance capacity, but the data show no consistent trends. In humans, the evidence is limited: A study (n = 3) found that endurance performance measured at 70 to 75 percent VO2max decreased after consumption

FIGURE B-5 Endurance time to exhaustion in sedentary and trained male rats after four weeks’ adaptation to one of two fat-rich diets containing either unsaturated or saturated fatty acids or to a carbohydrate-rich diet.

NOTE: Values are means ± standard error (n = 7–11). CHO = carbohydrate; MONO = monounsaturated fat; n = number in sample; SAT = saturated fat. * = significantly different from the sedentary groups (p < 0.05).

SOURCE: Helge et al. (1998a).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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of a polyunsaturated fat-rich diet as compared with a saturated-fat diet (Lukaski et al., 2001). The author’s unpublished observations found that the consumption of a saturated-fat diet, versus a polyunsaturated-fat diet, had no effect on endurance performance. Thus, insufficient data are available to support a role for dietary fatty acid composition on exercise performance.

Fatty Acids and Health Considerations

Are there adverse or positive effects of including different fatty acids in the ration? This question includes a number of complex issues that are incompletely resolved; space limitations prevent their being addressed here, but the following list of potential roles for dietary fatty acids should be considerd for further research:

  • The influence of dietary fatty acid composition on membrane function (Pan et al., 1994).

  • The influence of dietary fatty acid composition (particularly the content of n-3 and n-6 fatty acids) on immune function (Venkatraman et al., 2000).

  • The potential hypolipedemic effects of n-3 fatty acids (Harris, 1997).

  • The effects of saturated fatty acids on decreasing insulin sensitivity (Pan et al., 1994).

  • The interactions with and effects of specific fatty acids on gene expression in muscle (Spriet and Gibala, 2004; Venkatraman et al., 2000).

The amount of physical activity performed by these soldiers as well as their good training status suggests that shorter term modifications of dietary fatty acid composition and dietary fat content would have insignificant effects on their general health and function.

SUMMARY

The following arguments confer positive and negative aspects of adding increased amounts of fat to the ration. The positive effects of adding more fat include an increased energy content of the ration and a faster repletion of muscle triacylglycerol stores. The negative effects of adding more fat include increased rates of perceived exertion and mental strain during physical activity and a potential lowering of muscle glycogen stores (possibly liver glycogen). There may be an additional increased risk of inducing higher ketone levels but, in my opinion, such a risk does not pose a problem in this situation.

Insufficient evidence exists to verify the effects of specific dietary fatty acids on performance capacity. Some data suggest health and metabolic benefits from the consumption of specific fatty acids. However, in fit and healthy younger men exposed to intense physical activity, these effects, if indeed present, would have more influence on long-term health status rather than on short-term exer-

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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cise capacity and health. Therefore, the fatty acid composition in the ration should adhere to the requirements established by the Institute of Medicine (IOM, 2002).

Based on the issues addressed above the recommendations for the ration are the following:

  • The fat content in the ration can be between 30 to 50 percent (of total energy) without reducing physical capacity; however, increasing the fat content may lead to slightly higher mental strain.

  • When protein requirements are met and sufficient carbohydrate for high-intensity tasks is given, fat can be used to increase the energy content of the ration.

  • While no specific fatty acid types improve performance, adequate essential fatty acids must be included in the ration at the current recommended levels (IOM, 2002).

ACKNOWLEDGMENTS

The author is affiliated with the Copenhagen Muscle Research Centre, which is supported by grants from the University of Copenhagen, from the faculties of science and of health sciences at this university, and from the Copenhagen Hospital Corporation.

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Decombaz J, Schmitt B, Ith M, Decarli B, Diem P, Kreis R, Hoppeler H, Boesch C. 2001. Postexercise fat intake repletes intramyocellular lipids but no faster in trained than in sedentary subjects. Am J Physiol Regul Integr Comp Physiol 281(3):R760–R769.


Galbo H, Holst JJ, Christensen NJ. 1979. The effect of different diets and of insulin on the hormonal response to prolonged exercise. Acta Physiol Scand 107(1):19–32.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Harris WS. 1997. n-3 Fatty acids and serum lipoproteins: Human studies. Am J Clin Nutr 65(5 Suppl):1645S–1654S.

Helge JW. 2000. Adaptation to a fat-rich diet. Effects on endurance performance in humans. Sports Med 30(5):347–357.

Helge JW. 2002. Long-term fat diet adaptation effects on performance, training capacity, and fat utilization. Med Sci Sports Exerc 34(9):1499–1504.

Helge JW, Ayre K, Chaunchaiyakul S, Hulbert AJ, Kiens B, Storlien LH. 1998a. Endurance in high-fat-fed rats: Effects of carbohydrate content and fatty acid profile. J Appl Physiol 85(4):1342–1348.

Helge JW, Lundby C, Christensen DL, Langfort J, Messonnier L, Zacho M, Andersen JL, Saltin B. 2003. Skiing across Greenland icecap: Divergent effects on limb muscle adaptations and substrate oxidation. J Exp Biol 206(Pt 6):1075–1083.

Helge JW, Wulff B, Kiens B. 1998b. Impact of a fat-rich diet on endurance in man: Role of the dietary period. Med Sci Sports Exerc 30(3):456–461.

Hultman E, Nilsson L. 1971. Liver glycogen in man. Effect of different diets and muscular exercise. In: Pernow B, Saltin B, eds. Muscle Metabolism During Exercise. Proceedings of a Karolinska Institutet Symposium held in Stockholm, Sweden, September 6–9, 1970. New York: Plenum. Pp. 143–151.


IOM (Institute of Medicine). 2002. Dietary Reference Intakes. Energy, Carbohydrates, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press.


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Pan DA, Hulbert AJ, Storlien LH. 1994. Dietary fats, membrane phospholipids and obesity. J Nutr 124(9):1555–1565.

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Stepto NK, Carey AL, Staudacher HM, Cummings NK, Burke LM, Hawley JA. 2002. Effect of short-term fat adaptation on high-intensity training. Med Sci Sports Exerc 34(3):449–455.


Venkatraman JT, Leddy J, Pendergast D. 2000. Dietary fats and immune status in athletes: Clinical implications. Med Sci Sports Exerc 32(7 Suppl):S389–S395.


Wagner GN, Balfry SK, Higgs DA, Lall SP, Farrell AP. 2004. Dietary fatty acid composition affects the repeat swimming performance of Atlantic salmon in seawater. Comp Biochem Physiol A Mol Integr Physiol 137(3):567–576.

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Carbohydrate–Protein Balance for Physical Performance

Kevin D. Tipton, University of Birmingham, UK

INTRODUCTION

Proper nutrition for military personnel has long been an important consideration for military planners. Nutrition may be especially important for military combat personnel performing duties that entail short-term, strenuous physical tasks in high-stress situations. Stress during military operations results from a combination of increased energy expenditure, decreased energy intake, and a lack of sleep for extended periods. These multiple stressors on mental and physical capabilities may decrease muscle performance enough to compromise both lives and military success. Sufficiently effective nutrients in combat rations would enhance the soldiers’capabilities and reduce both the loss of combat effectiveness and the number of casualties. Protein and carbohydrate consumption may contribute to optimal muscle performance during these situations.

The unique circumstances in the field make it difficult for soldiers to consume sufficient protein and carbohydrate as well as overall energy during their missions. For example, weight and size that soldiers can carry is limited and evidence shows that high-stress combat can suppress appetite (Popper et al., 1989). These factors lead to large energy deficits and macronutrient deficiencies for the three- to seven-day periods of these operations. These energy and macronutrient deficits could lead to metabolic disturbances that impair muscular performance during demanding and intense military operations.

The combination of stressors—decreased energy and protein intake, sleep deprivation, extreme physical activity, and high stress levels—that soldiers face

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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during these missions represents a complex and unique situation. Unfortunately, little, if any, direct information is available about muscular metabolic response to these stressors and about the appropriate nutrient intake that would be optimal for these capabilities.

This review uses data collected during periods of physiological stress to develop strategies to enhance protein and carbohydrate intake during sustained military operations. Because of a paucity of such data, however, this review provides a speculative guideline for recommendations. The following are specific questions that this review addresses:

  • What would be the optimal macronutrient balance between protein and carbohydrate for an assault ration to enhance muscle performance during combat missions? Does the intensity of activity (i.e., high-tempo, stressful, repetitive combat missions) alter the optimal balance?

  • What protein intake is recommended to best sustain homeostasis while people are eating reduced calories and exercising?

  • What are the types and levels of macronutrients (e.g., complex versus simple carbohydrates, proteins with specific amino acid profiles, other sources of nitrogen, etc.) that would optimize such an assault ration to enhance muscle performance during combat missions?

ENERGY INTAKE AND PHYSICAL ACTIVITY

Energy intake plays a major role in body protein metabolism. Operational requirements, as noted above, limit the intake of available energy in rations during short-term, high-stress missions. Such limitations in energy intake, combined with high levels of physical activity, ensure that participants are in an energy deficit for the three- to seven-day duration of a mission. Measurements made during simulated sustained operations do not clearly demonstrate muscle loss (Montain and Young, 2003; Nindl et al., 2002); however, body composition measures may not have the sensitivity to detect small changes over a short time. Nevertheless, the evidence provided below suggests that energy deficits that occur during these missions will lead to muscle loss.

Many classic studies from the laboratory of Calloway and Butterfield have demonstrated the importance of energy balance to maintain body nitrogen balance. Todd and colleagues (1984) clearly demonstrated that nitrogen balance is better maintained when energy balance is positive or, at least, zero (Figure B-6). Nitrogen balance could not be maintained when energy intake was 15 percent less than energy output. Presumably, the body’s predominant and accessible source, muscle protein, would also be the major site of this nitrogen loss. Energy restriction over longer periods (e.g., 10 weeks) results in the loss of lean mass during very low calorie dieting (Layman et al., 2003); however, the metabolic mechanisms for this loss remain unexplained.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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FIGURE B-6 Nitrogen (N) balance during differing levels of energy intake (E) and physical activity (X) at two different levels of protein intake. Each bar is at either energy balance or 15 percent deficit due to increased exercise. These data illustrate that nitrogen balance is negative during energy deficits and improved by low-intensity exercise. Nitrogen balance is not positive in any combination of energy intake and exercise on the lowest (0.57 g·kg–1·d–1) level.

SOURCE: Adapted from Todd et al. (1984).

Muscle protein synthesis is reduced by 65 percent in food-deprived rats (Anthony et al., 2000), and perturbations in muscle metabolism from energy deficits could occur very rapidly. Recently, Tipton et al. (2003) demonstrated that the release of amino acids from leg muscle in healthy volunteers occurred in the first 24 h of energy restriction (80 percent of their weight maintenance levels). In that study, the volunteers were resting and consumed their habitual level of dietary protein. It seems that reducing energy intake by only 20 percent immediately stimulates a catabolic situation in muscle, suggesting that soldiers participating in missions where their energy intake is half of their energy output would be losing nitrogen, most likely from muscle. Unfortunately, it is not clear how the energy restriction and negative energy balance inherent for these sustained operations reduces muscle performance (Friedl, 1995).

A portion of the uncertainty about the effects of energy balance on muscle performance in short-term military missions with concomitant stressors, such as high-physical activity, sleep loss, and dietary restrictions, can be attributed to the complexity of the situation and the lack of information from studies. Protein use can be improved by physical activity (Butterfield and Calloway, 1984; Todd et al., 1984) (Figure B-6). Increased energy intake to support increased physical

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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activity improves the nitrogen balance, and the physical activity improves nitrogen retention (Butterfield and Calloway, 1984; Todd et al., 1984). Following an acute bout of resistance exercise, muscle protein synthesis and net muscle protein balance are increased, even in trained individuals (Biolo et al., 1995; Phillips et al., 1997, 1999). Muscle protein synthesis was increased following four hours of walking (Carraro et al., 1990), but no balance data are available for that type of activity.

Whereas these data could be interpreted to suggest that the physical activity common during military maneuvers may improve protein balance and have a good effect on muscle protein, there are reasons to believe otherwise. There is typically a period of adaptation to physical activity in which nitrogen balance is diminished (Butterfield, 1987; Butterfield and Calloway, 1984; Gontzea et al., 1975). This transient increase in protein loss peaks at four to ten days following initiation of the exercise program; easily encompassing the time typically used for these missions. However, these data are from untrained individuals initiating physical activity, so the applicability of these data to the situations being discussed for soldiers is unclear. It is easy to accept that the habitual level of training before participating in difficult missions could be protective, but there are no data to support this contention. Furthermore, the data supporting a benefit to nitrogen balance from activity were obtained during an energy balance (Todd et al., 1984). Positive nitrogen balance could not be maintained when energy balance was negative, despite increased physical activity (Figure B-6). Thus, it seems that the conditions intrinsic to the sustained operations missions will result in negative nitrogen balance and loss of muscle protein.

The intensity of the activity necessary for successful completion of the missions may increase the loss of muscle protein and, thus, exacerbate the effects of the negative energy balance. Given that the logistical limitations to the rations for these missions preclude carrying additional rations to accommodate the increased activity, any increase in activity will result in increased energy deficits. Furthermore, there is evidence that high-intensity exercise is debilitating for muscle protein metabolism. Whereas muscle protein synthesis has been demonstrated to increase following both resistance (Biolo et al., 1995; Phillips et al., 1997, 1999) and endurance (Carraro et al., 1990) exercise in humans, it is depressed following prolonged, high-intensity exercise in rats (Anthony et al., 1999; Gautsch et al., 1998). It is possible that species-specific differences in the response of muscle to exercise may explain the differential. On the other hand, the response of muscle protein synthesis to resistance exercise in rats (Farrell et al., 1999; Hernandez et al., 2000) is similar to that for humans (Biolo et al., 1995; Phillips et al., 1997, 1999). It is more likely that the intensity of the exercise during the treadmill running was severe and resulted in decreased muscle protein synthesis. The rats ran at approximately 80 percent of VO2max for approximately two hours, roughly equivalent to the effort that only an elite runner could maintain for a marathon. Furthermore, if relative life span is taken into

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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account, two hours on a treadmill for a rat could be considered equivalent to the effort of several days for humans. Thus, it is conceivable that this intense physical exercise would also result in reduced muscle protein synthesis in humans. The evidence presented suggests that, rather than increasing protein use, the physical activity involved in prolonged military missions may be detrimental to muscle protein metabolism. The energy deficit, combined with high-tempo, stressful physical activity, suggests that muscle protein metabolism will be altered during missions of this type.

Protein Intake

As with energy intake, protein intake during these missions can be limited by operational factors. There is a great deal of controversy in the sports science community about the protein requirements for athletes and active individuals; however, little question remains that increased protein intake would be advantageous in an energy deficit made worse by high levels of physical activity. Todd and colleagues (1984) demonstrated that, at low levels of protein intake (0.57 g/kg per day), nitrogen balance was negative during both energy balance and energy deficit. Increasing protein intake from 0.57 to 0.85 g/kg per day improved nitrogen balance when energy intake was 15 percent less than energy output (Figure B-6). Either way, nitrogen balance was negative during both intakes. At this time, there is no way to determine if the loss of body protein could be ameliorated by higher protein intakes and, if so, what would constitute the optimal level of protein intake. A question also remains of a ceiling effect whereby no further improvement is possible with increased protein intake. Unknown as well is whether positive balance is feasible during the conditions inherent to military operations. In addition, it is impossible to determine whether eliminating negative nitrogen balance is necessary to improve the performance and health of the military. A recent study demonstrated that a greater proportion of weight lost during energy restriction comes from fat, rather than lean, mass when protein intake is increased (Layman et al., 2003). Data from this study suggest that increasing protein intake spares body protein during periods of negative energy balance. However, the applicability to soldiers during sustained operations is limited because this study was conducted on obese female subjects in weight-loss situations and did not involve exercise.

Loss of nitrogen likely is exacerbated by the combination of higher protein intakes before missions and lower protein intake during missions. Millward and colleagues demonstrated that body protein is lost when dietary protein intake is decreased (Pacy et al., 1994; Price et al., 1994; Quevedo et al., 1994). Data from these studies suggest an adaptation period that takes several days (often the time expected for most of these missions) (Figure B-7). These data also suggest that the sudden decline in protein intake expected when soldiers undertake these missions would contribute to a loss of body proteins, most likely from muscle.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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However, in these studies, the subjects were in energy balance and did not exercise, so it is unclear how applicable these data are to sustained operations.

The available information suggests that decreasing protein intake during these missions will be detrimental to muscle protein metabolism. The recommendation to maximize protein intake during the missions seems prudent; however, there are sufficient questions to prevent a specific recommendation from being made with any confidence.

Carbohydrate and Lipid Intake

There is no question that carbohydrate intake is critical for optimal muscle performance during strenuous activity. Maintenance of blood glucose and glycogen for muscle fuel are important for muscular performance (Burke et al., 2004; Coyle, 2004; Hargreaves et al., 2004). Several studies have demonstrated that increased carbohydrate intake improved performance in military tasks (Montain and Young, 2003; Montain et al., 1997). Severe muscle glycogen depletion has been shown during four- to five-day field operations (Jacobs et al., 1983). Although provision of extra carbohydrates did not increase the glycogen levels in these soldiers (Jacobs et al., 1983) sufficient carbohydrate intake seems important for performance maintenance during sustained military operations (Montain and Young, 2003).

Carbohydrate intake may also enhance muscle protein metabolism. Acute provision of carbohydrates increases net muscle protein balance following exercise,

FIGURE B-7 Change in nitrogen (N) balance due to change from the first three days of high-protein (HP) to low-protein (LP) intake.

SOURCE: Quevedo et al. (1994).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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presumably through the action of insulin (Borsheim et al., 2004b). Nevertheless, any increase in net muscle protein balance from ingestion of carbohydrate is much less than that from ingestion of an amino acid source (Borsheim et al., 2004a; Miller et al., 2003). On a whole body level, Gaudichon and colleagues (1999) demonstrated that carbohydrate ingestion increased postprandial use of dietary protein to a greater extent than did lipids. It is likely that increased use of available nutrients by the body is especially important in situations of limited nutrient availability. Replacing carbohydrate with fat has been demonstrated to increase nitrogen balance during hypocaloric situations (Richardson et al., 1979). On the other hand, Boirie and colleagues have presented a series of studies (Boirie et al., 1997; Dangin et al., 2003) suggesting that, after protein ingestion, amino acids released slowly into the blood provide a superior anabolic response. Given that lipids do slow the digestion of nutrients, it could be argued that lipids may improve the anabolic response in the muscle. We recently tested this notion in our laboratory, and despite equivalent protein ingestion during two small, separate meals, net muscle protein balance was greater from proteins when fat was included in the meal (Elliot et al., unpublished data). Thus, including both carbohydrates and lipids in the ration should maximize the accretion of ingested protein into muscle when nutrients are limited. The exact composition of such nutrients remains unknown.

Intake of Amino Acids

Amino acids provided by protein ingestion stimulate the accretion of muscle protein. Evidence from acute metabolic studies suggests that increased muscle protein synthesis and net muscle protein synthesis result only from the provision of essential amino acids; that is, nonessential amino acids are unnecessary to stimulate muscle protein accretion (Borsheim et al., 2002; Tipton and Wolfe, 2001; Tipton et al., 1999, 2003). Furthermore, the response of muscle protein balance to essential amino acids seems dose dependent (Borsheim et al., 2002). Aside from increasing amino acid availability for protein synthesis, essential amino acids may act as signals for stimulating protein synthesis. Essential amino acids, particularly leucine, activate translational signaling (Anthony et al., 2000; Kimball and Jefferson, 2001; Kimball et al., 2002). In rats, leucine stimulates muscle protein synthesis that was diminished by severe exercise (Anthony et al., 1999), but feeding carbohydrates only did not (Gautsch et al., 1998). Essential amino acids may be particularly effective during sustained operations when physical activity is extreme.

More evidence for the potential efficacy of essential amino acids during sustained military operations comes from acute metabolic studies performed in our laboratory. Following resistance exercise, ingesting 12 g of essential amino acids resulted in an amino acid uptake that was more than double that from ingesting 20 g of whole proteins (Borsheim et al., 2002; Tipton et al., 2004)

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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(Figure B-8). Consuming only 60 percent of the volume more than doubled the anabolic response, which means a superior response was obtained for less mass/volume. Furthermore, essential amino acids, combined with exercise, ameliorated the amino acid release from muscle in response to a 20 percent energy deficit (Tipton et al., 2003). These factors suggest that essential amino acids could be important for ration design.

SUMMARY

The metabolic demands endured by soldiers on sustained military operations are severe and unique. Very little research exists that specifically examines the results from missions that involve underfeeding and high-activity levels as well as high stress on muscle metabolism and performance. The indirectly available information suggests that optimal ration development should include maximizing the energy and protein content within the operational limits. Carbohydrate and fat are clearly important, but it is unclear what quantity each should represent in the overall composition. Recent evidence from acute metabolic studies suggests that essential amino acids may be an important component of a ration for sustained missions. The anabolic response to essential amino acids seems to be superior to a larger amount of intact protein, thus offering higher efficiency. Further research is necessary to determine the effects of these various nutrients on muscle metabolism and performance in specific situations experienced during sustained military operations.

FIGURE B-8 Phenylalanine uptake during three hours (h) following ingestion of 12 g of free essential amino acids (EAA), 20 g of casein (CS), or 20 g of whey proteins (WP).

SOURCE: Borsheim et al. (2002); Tipton et al. (2004).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Gontzea I, Sutzescu P, Dumitrache S. 1975. The influence of adaptation to physical effort on nitrogen balance in man. Nutr Rept Intern 11:231–236.


Hargreaves M, Hawley JA, Jeukendrup A. 2004. Pre-exercise carbohydrate and fat ingestion: Effects on metabolism and performance. J Sports Sci 22(1):31–38.

Hernandez JM, Fedele MJ, Farrell PA. 2000. Time course evaluation of protein synthesis and glucose uptake after acute resistance exercise in rats. J Appl Physiol 88(3):1142–1149.


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Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Kimball SR, Jefferson LS. 2001. Regulation of protein synthesis by branched-chain amino acids. Curr Opin Clin Nutr Metab Care 4(1):39–43.

Kimball SR, Farrell PA, Jefferson LS. 2002. Invited review: Role of insulin in translational control of protein synthesis in skeletal muscle by amino acids or exercise. J Appl Physiol 93(3):1168–1180.


Layman DK, Boileau RA, Erickson DJ, Painter JE, Shiue H, Sather C, Christou DD. 2003. A reduced ratio of dietary carbohydrate to protein improves body composition and blood lipid profiles during weight loss in adult women. J Nutr 133(2):411–417.


Miller SL, Tipton KD, Chinkes DL, Wolf SE, Wolfe RR. 2003. Independent and combined effects of amino acids and glucose after resistance exercise. Med Sci Sports Exerc 35(3):449–455.

Montain SJ, Young AJ. 2003. Diet and physical performance. Appetite 40(3):255–267.

Montain SJ, Shippee RL, Tharion WJ. 1997. Carbohydrate-electrolyte solution effects on physical performance of military tasks. Aviat Space Environ Med 68(5):384–391.


Nindl BC, Leone CD, Tharion WJ, Johnson RF, Castellani JW, Patton JF, Montain SJ. 2002. Physical performance responses during 72 h of military operational stress. Med Sci Sports Exerc 34(11):1814–1822.


Pacy PJ, Price GM, Halliday D, Quevedo MR, Millward DJ. 1994. Nitrogen homeostasis in man: The diurnal responses of protein synthesis and degradation and amino acid oxidation to diets with increasing protein intakes. Clin Sci 86(1):103–118.

Phillips SM, Tipton KD, Aarsland A, Wolf SE, Wolfe RR. 1997. Mixed muscle protein synthesis and breakdown after resistance exercise in humans. Am J Physiol 273(1 Pt 1):E99–E107.

Phillips SM, Tipton KD, Ferrando AA, Wolfe RR. 1999. Resistance training reduces the acute exercise-induced increase in muscle protein turnover. Am J Physiol 276(1 Pt 1):E118–E124.

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Quevedo MR, Price GM, Halliday D, Pacy PJ, Millward DJ. 1994. Nitrogen homoeostasis in man: Diurnal changes in nitrogen excretion, leucine oxidation and whole body leucine kinetics during a reduction from a high to a moderate protein intake. Clin Sci 86(2):185–193.


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Tipton KD, Borsheim E, Wolf SE, Sanford AP, Wolfe RR. 2003. Acute response of net muscle protein balance reflects 24-h balance after exercise and amino acid ingestion. Am J Physiol Endocrinol Metabol 284(1):E76–E89.

Tipton KD, Elliott TA, Cree MG, Wolf SE, Sanford AP, Wolfe RR. 2004. Ingestion of casein and whey proteins result in muscle anabolism after resistance exercise. Med Sci Sports Exerc 36(12):2073–2081.

Tipton KD, Ferrando AA, Phillips SM, Doyle D Jr, Wolfe RR. 1999. Postexercise net protein synthesis in human muscle from orally administered amino acids. Am J Physiol 276(4 Pt 1):E628–E634.

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Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Carbohydrate Ingestion During Intense Activity

Edward F. Coyle, University of Texas at Austin

INTRODUCTION

The Committee on Optimization of Nutrient Composition of Military Rations for Short-Term, High-Stress Situations was charged with making recommendations on the composition of a food ration (assault ration) that will best sustain physical and cognitive performance for short-term use by highly-trained soldiers during high-tempo, stressful, repetitive combat missions; in addition, the food ration will also prevent possible adverse health consequences under the conditions of a hypocaloric diet. Stress may be due to high physical and cognitive workloads such as exercise, extreme environmental temperature, dehydration, heat exhaustion, threat to personal safety, sleep deprivation, and other operational demands. Important health concerns for soldiers during combat missions are the optimization of gastrointestinal processes and prevention of diarrhea, dehydration, hyperthermia, kidney stones; optimization of the function of immune system; and prevention of infections. The expected daily expenditure of these soldiers is approximately 4,000 to 4,500 kcal/day. The assault ration will provide approximately 2,400 kcal/day for three to seven days with one to three days of recovery.

This paper focuses on several aspects of the design of such a ration. Although a lot of the literature presented is from the sports and exercise community, their conclusions can be used to support recommendations for the assault ration described above. This paper attempts to answer the following questions:

  • What would be the optimal amount of carbohydrates for an assault ration to enhance performance during combat missions?

  • What are the types and levels of macronutrients (e.g., complex verses simple carbohydrates) that would optimize an assault ration to enhance performance during combat missions?

  • How much is performance going to decline when there is a reduction in both carbohydrates and calories?

CARBOHYDRATE INTAKE DURING EXERCISE

Despite long-ago evidence that carbohydrate ingestion during exercise improved athletic performance, the discovery in the 1960s and 1970s of muscle glycogen’s importance as a source of carbohydrate energy for athletes (Bergstrom et al., 1967) seemed to have overshadowed, until the mid-1980s, the potential energy contribution from carbohydrate ingested during the period of exercise (Coggan and Coyle, 1991; Coyle et al., 1986; Hargreaves, 1996). Costill and

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Miller (1980) emphasized the need for fluid intake during exercise but recommend against ingesting very much carbohydrate. This recommendation is understandable for that period of time, given that the physiological benefits of fluid replacement were beginning to be established, as reflected in the 1975 American College of Sports Medicine (ACSM) position-statement, whereas the physiological benefits of carbohydrate ingestion for blood glucose supplementation as well as the physiological mechanisms explaining this benefit were not yet established (Hargreaves, 1996). In the 1980s, the observation that adding carbohydrate to water temporarily slowed the gastric emptying rate was interpreted to suggest that fluid replacement solutions should not contain much carbohydrate (Coyle et al., 1978). It was also thought, albeit mistakenly, that “ingested glucose contributes very little to the total energy utilized during exercise” (Costill and Miller, 1980). Therefore, the prevailing recommendation in 1980 was that “under conditions that threaten the endurance athlete with dehydration and hyperthermia, fluid replacement solutions should contain little sugar (> 25 g/L or > 2.5 percent) and electrolytes” (Costill and Miller, 1980).

Later in the 1980s, it was established that ingested carbohydrate and blood glucose can indeed be oxidized at rates of approximately 1 g/minute and that this exogenous carbohydrate becomes the predominant source of energy late in a bout of prolonged, continuous exercise (Convertino et al., 1996). Carbohydrate ingestion can delay muscle fatigue during prolonged cycling and running, and it also improves the power output that can be maintained (Hargreaves, 1996; Millard-Stafford, 1992; Millard-Stafford et al., 1997). It is now understood that the slight slowing of gastric emptying caused by solutions containing up to 8 percent of carbohydrate is a relatively minor factor in fluid replacement rate compared with the large influence of increased fluid volume for increasing gastric emptying and fluid replacement rate (Coyle and Montain, 1992a, b; Maughan, 1991; Maughan and Noakes, 1991; Maughan et al., 1993). Therefore, it is generally recommended that endurance athletes ingest carbohydrate at a rate of 30 to 60 g/h (Casa et al., 2000; Convertino et al., 1996). The type of carbohydrate can be glucose, sucrose, maltodextrins, or some high-glycemic starches. Fructose intake should be limited to amounts that do not cause gastrointestinal discomfort (Casa et al., 2000; Convertino et al., 1996). This rate of carbohydrate ingestion can be met by drinking solutions containing 4 to 8 percent of carbohydrates (4 to 8 g/100 mL) (Casa et al., 2000; Convertino et al., 1996; Rehrer, 1994; Rehrer et al., 1993).

Performance During Short-Term, Intermittent High-Intensity Exercise

Benefits of carbohydrate ingestion during performance of high-intensity, intermittent exercise attempted after at least 60 minutes of continuous moderate-intensity exercise (i.e., 65 to 80 percent VO2max) was the focus of study beginning in the late 1980s. Power output measured over 5 to 15 minutes of high-

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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intensity and predominantly aerobic exercise has been generally observed to increase by ingesting carbohydrate (Coggan and Coyle, 1988; Mitchell et al., 1989; Murray et al., 1987; Sugiura and Kobayashi, 1998) In the 1996 ACSM position statement on Exercise and Fluid Replacement, it was concluded that “During intense exercise lasting longer than 1 h, it is recommended that carbohydrates be ingested at a rate of 30–60 g/h to maintain oxidation of carbohydrates and delay fatigue” (Convertino et al., 1996).

During the past decade, attention has focused on determining if carbohydrate intake during sporting events such as soccer and tennis improves various indices of performance. As discussed below, carbohydrate ingestion appears to frequently benefit performance as demonstrated in tests of “shuttle-running” ability, which simulates the stop-and-start nature of many sports requiring bursts of speed and some fatigue resistance (Nicholas et al., 1995). Physiological mechanisms for this ergogenic effect of carbohydrate ingestion are not clear and have been theorized to involve more than simply skeletal muscle metabolism, implying a neuromuscular component. The challenges now are identifying the types of physical activity and sporting situations during which carbohydrate ingestion is advisable and those during which such a recommendation is not effective or even counterproductive.

Conditions During Which Carbohydrate Ingestion During Exercise Does Not Appear to Improve Performance

Performance or fatigue resistance can be governed by numerous physiological factors involving, primarily, the skeletal muscle, the cardiovascular system, and the nervous system. Some primary causes of fatigue are not influenced by carbohydrate ingestion during exercise; for example, the negative effects of hyperthermia on performing prolonged exercise in a hot environment [e.g., 33°C to 35°C (91.4°F to 96°F)] do not appear to be lessened by carbohydrate ingestion (Febbraio et al., 1996; Fritzsche et al., 2000). However, during exercise in a cool environment [i.e., 5°C (41°F)] (Febbraio et al., 1996) that is not limited by hyperthermia, or when subjects drink fluids during exercise in a hot environment and also do not become hyperthermic (Fritzsche et al., 2000), carbohydrate ingestion improves performance. Under conditions not eliciting hyperthermia, the most important factor for performing prolonged, intense exercise appears to be maintaining carbohydrate availability and thus carbohydrate oxidation, especially from blood glucose oxidation as muscle glycogen concentration declines. This goal was better achieved by ingesting 7 percent carbohydrate solutions as compared with a 14 percent solution (Febbraio et al., 1996).

Another example of a condition when carbohydrate ingestion during exercise would not be expected to improve performance is when the cause of fatigue is the accumulation of hydrogen ion in skeletal muscle (e.g., low muscle pH), as occurs during a single bout of intense exercise performed continuously for 2 to

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

30 minutes. Performing exercise that is not sufficiently stressful to cause fatigue, as evidenced by reduced power production, or that does not require high levels of effort to maintain power, as reflected, for example, by high levels of various stress hormones, would not benefit from carbohydrate ingestion. Furthermore, carbohydrate intake is not generally recommended during events, performed either continuously or intermittently, that are completed in 30 to 45 minutes or less. Although this last concept has not been extensively studied to date, it is a valid assumption based on the practices of athletes competing in events lasting only 30 to 45 minutes. As discussed, carbohydrate ingestion does not appear to lessen fatigue from hyperthermia or dehydration-induced hyperthermia, even when the durations of exercise are prolonged (e.g., one to three hours) (Febbraio et al., 1996; Fritzsche et al., 2000). Thus, there does not appear to be any benefit of adding carbohydrate to fluid replacement solution under these conditions. Accordingly, people who exercise at moderate intensity for less than one hour and do not experience fatigue do not appear to benefit from carbohydrate ingestion during exercise. Yet ingesting carbohydrate at a rate of 30 to 60 g/h does not appear to present a general physiological risk to people who do not experience gastrointestinal discomfort.

Conditions During Which Carbohydrate Ingestion Improves Performance through Unexplained Physiological Mechanisms

Carbohydrate ingestion during prolonged exercise can benefit performance if inadequate carbohydrate energy from blood glucose is the cause of fatigue (Coggan and Coyle, 1991; Febbraio et al., 1996). This effect on performance is a well-documented physiological mechanism by which the ergogenic benefit of carbohydrate ingestion during exercise can be explained. However, carbohydrate ingestion has been observed to improve performance under conditions in which fatigue is not clearly caused by a lack of aerobic or anaerobic carbohydrate energy. For example, when the duration of continuous exercise is extended to approximately 60 minutes and thus the intensity is 80 to 90 percent VO2max, carbohydrate ingestion during exercise has been shown to improve power output by 6 percent during the 50- to 60-minute period (Below et al., 1995).

Other recent studies have also reported a performance benefit of carbohydrate feeding when the total duration of the performance bout is approximately 60 minutes or more by breaking the time into shorter exercise durations, thereby simulating the demands of many sports (basketball, soccer, hockey) in which high-intensity exercise is interspersed with periods of recovery (Mitchell et al., 1989; Murray et al., 1987). Carbohydrate ingestion is ergogenic during 15-minute bouts of intermittent “shuttle running,” performed numerous times (e.g., five times) as well as during repeated high-intensity intervals of one minute’s duration and a three-minute recovery (Davis et al., 1997, 1999, 2000; Nicholas et al., 1995; Welsh et al., 2002). The total duration of these work–rest bouts was more

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

than 60 minutes. The physiological mechanisms responsible for these performance benefits from carbohydrate ingestion are not clear and have been theorized to involve the central nervous system, skeletal muscle, and the cardiovascular system. It is likely that carbohydrate feeding influences the interactions of all three systems, possibly through the actions of neurotransmitters, hormones, and peptides that are already known (e.g., insulin, catecholamines, and serotonin), that are newly recognized (e.g., interluken-6), or that have yet to be discovered. Regardless, sufficient evidence is accumulating to recommend carbohydrate ingestion during exercise bouts of continuous or intermittent exercise that lasts for 60 minutes or longer and cause fatigue from factors other than hyperthermia.

Can Carbohydrate Ingestion During Exercise Be Counterproductive?

It is recommended that carbohydrate be ingested at a rate of 30 to 60 g/h during exercise (Convertino et al., 1996), recognizing that ingesting more does not increase oxidation rate but can produce gastrointestinal discomfort in many people (Rehrer et al., 1992; Wagenmakers et al., 1993). In the latter case, carbohydrate feeding can be counterproductive when ingested in amounts (> 60 to 90 g/h) or concentrations (> 7 to 8 percent) that are too large (Febbraio et al., 1996; Galloway and Maughan, 2000).

If it produced gastrointestinal discomfort, carbohydrate ingestion at 30 to 60 g/h during exercise can impair performance as compared with no carbohydrate ingestion, a factor that is likely to vary from sport to sport and athlete to athlete. Carbohydrate ingestion should be used with caution during events lasting approximately 15 to 45 minutes and requiring repeated bouts of intense exercise lasting several minutes followed by several minutes of rest because these events may cause large swings in blood glucose and insulin concentration. Feeding plans must be specific to the varied intensity and time demands of the event. Those feeding schedules might be more than those described below, yet without data or experience to make more specific recommendations; all that can be done at present, besides recognizing these limitations, is to encourage systematic trial and error.

From a practical perspective, the recommendation of ingesting 30 to 60 g/h of carbohydrate during exercise should emphasize that this be accomplished by taking feedings every 10 to 30 minutes, as allowed by the event. The goal of the feeding schedule should be to create a steady flow of carbohydrate into the blood stream, which will then provide a steady flow of exogenous glucose into the blood. In other words, if carbohydrate feeding is begun during an event, it should be continued throughout the event in a manner that allows for a steady flow of exogenous glucose into the blood with minimal gastrointestinal discomfort. Avoid giving a large bolus of carbohydrate (i.e., more than 30 to 60 g) early in an event and then discontinuing carbohydrate feeding. This practice will prime the body for glucose metabolism, reduce fat oxidation, and then deprive the body of the fuel it has been primed to metabolize.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×
Summary and Recommendations for Carbohydrate Intake During Exercise

During exercise that lasts longer than one hour and that causes fatigue, physically active people are advised to ingest 30 to 60 g/h of carbohydrate that can be rapidly converted to blood glucose because doing so generally improves performance. There is not a clear physiological need to consume any fluid or fuel when beginning exercise while reasonably hydrated and proceeding to exercise at low or moderate intensity for less than one hour without experiencing undo fatigue. However, there is no apparent reason for people to avoid fluid or carbohydrate intake if this is their preference and is well tolerated.

ACKNOWLEDGMENTS

The author is a member of the Sports Medicine Review Board of the Gatorade Sports Science Institute. Portions of this manuscript are similar to a recent review by the author published in 2004. Coyle EF. 2004. Fluid and fuel intake during exercise. Journal of Sports Sciences 22:39–55.

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Coggan AR, Coyle EF. 1991. Carbohydrate ingestion during prolonged exercise: Effects on metabolism and performance. Exerc Sport Sci Rev 19:1–40.

Convertino VA, Armstrong LE, Coyle EF, Mack GW, Sawka MN, Senay LC, Sherman WM. 1996. American College of Sports Medicine Position Stand on exercise and fluid replacement. Med Sci Sports Exerc 28(1):i–vii.

Costill D, Miller J. 1980. Nutrition for edurance sports. Carbohydrate and fluid balance. Int J Sports Med 1:2–14.

Coyle EF, Montain SJ. 1992a. Benefits of fluid replacement with carbohydrate during exercise. Med Sci Sports Exerc 24(9 Suppl):S324–S330.

Coyle EF, Montain SJ. 1992b. Carbohydrate and fluid ingestion during exercise: Are there trade-offs? Med Sci Sports Exerc 24(6):671–678.

Coyle EF, Coggan AR, Hemmert MK, Ivy JL. 1986. Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. J Appl Physiol 61(1):165–172.

Coyle EF, Costill DL, Fink WJ, Hoopes DG. 1978. Gastric emptying rates for selected athletic drinks. Res Q 49(2):119–124.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Davis JM, Jackson DA, Broadwell MS, Queary JL, Lambert CL. 1997. Carbohydrate drinks delay fatigue during intermittent, high-intensity cycling in active men and women. Int J Sport Nutr 7(4):261–273.

Davis JM, Welsh RS, Alerson NA. 2000. Effects of carbohydrate and chromium ingestion during intermittent high-intensity exercise to fatigue. Int J Sport Nutr Exerc Metab 10(4):476–485.

Davis JM, Welsh RS, De Volve KL, Alderson NA. 1999. Effects of branched-chain amino acids and carbohydrate on fatigue during intermittent, high-intensity running. Int J Sports Med 20(5):309–314.


Febbraio MA, Murton P, Selig SE, Clark SA, Lambert DL, Angus DJ, Carey MF. 1996. Effect of CHO ingestion on exercise metabolism and performance in different ambient temperatures. Med Sci Sports Exerc 28(11):1380–1387.

Fritzsche RG, Switzer TW, Hodgkinson BJ, Lee SH, Martin JC, Coyle EF. 2000. Water and carbohydrate ingestion during prolonged exercise increase maximal neuromuscular power. J Appl Physiol 88(2):730–737.


Galloway SD, Maughan RJ. 2000. The effects of substrate and fluid provision on thermoregulatory and metabolic responses to prolonged exercise in a hot environment. J Sports Sci 18(5):339–351.


Hargreaves M. 1996. Carbohydrates and exercise performance. Nutr Rev 54(4 Pt 2):S136–S139.


Maughan RJ. 1991. Fluid and electrolyte loss and replacement in exercise. J Sports Sci 9 (Spec No):117–142.

Maughan RJ, Noakes TD. 1991. Fluid replacement and exercise stress. A brief review of studies on fluid replacement and some guidelines for the athlete. Sports Med 12(1):16–31.

Maughan RJ, Goodburn R, Griffin J, Irani M, Kirwan JP, Leiper JB, MacLaren DP, McLatchie G, Tsintsas K, Williams C, Wellington P, Wilson WM, Wootton S. 1993. Fluid replacement in sport and exercise—A consensus statement. Br J Sport Med 27(1):34.

Millard-Stafford M. 1992. Fluid replacement during exercise in the heat. Review and recommendations. Sports Med 13(4):223–233.

Millard-Stafford M, Rosskopf LB, Snow TK, Hinson BT. 1997. Water versus carbohydrate-electrolyte ingestion before and during a 15-km run in the heat. Int J Sport Nutr 7(1):26–38.

Mitchell JB, Costill DL, Houmard JA, Fink WJ, Pascoe DD, Pearson DR. 1989. Influence of carbohydrate dosage on exercise performance and glycogen metabolism. J Appl Physiol 67(5):1843–1849.

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Nicholas CW, Williams C, Lakomy HK, Phillips G, Nowitz A. 1995. Influence of ingesting a carbohydrate-electrolyte solution on endurance capacity during intermittent, high-intensity shuttle running. J Sports Sci 13(4):283–290.


Rehrer NJ. 1994. The maintenance of fluid balance during exercise. Int J Sports Med 15(3):122–125.

Rehrer NJ, Beckers EJ, Brouns F, Saris WH, Ten Hoor F. 1993. Effects of electrolytes in carbohydrate beverages on gastric emptying and secretion. Med Sci Sports Exerc 25(1):42–51.

Rehrer NJ, Wagenmakers AJ, Beckers EJ, Halliday D, Leiper JB, Brouns F, Maughan RJ, Westerterp K, Saris WH. 1992. Gastric emptying, absorption, and carbohydrate oxidation during prolonged exercise. J Appl Physiol 72(2):468–475.


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Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Macronutrient Composition of Military Rations for Cognitive Performance in Short-Term, High-Stress Situations

Randall J. Kaplan, Canadian Sugar Institute

INTRODUCTION

The importance of nutrition for cognitive performance in military settings has long been recognized. The Committee on Military Nutrition Research (CMNR) of the Food and Nutrition Board, Institute of Medicine (IOM) of the National Academies has published several volumes on this topic, including reports on the cognitive effects of performance-enhancing food components (IOM, 1994); inadequate energy intakes (IOM, 1995); protein and amino acids (IOM, 1999); and caffeine (IOM, 2001).

Cognitive performance refers to intellectual behaviors such as memory, reasoning, attention, vigilance, and choice reaction time. Mood (e.g., happy, sad, calm, tense) and psychomotor performance (e.g., sensation, perception, agility) are distinct from cognitive performance, but they can have a considerable influence on it (Mays, 1995; Spring et al., 1994) and are therefore relevant to this discussion. The aspects of cognition that are important in combat settings include the ability to perceive, attend to, and respond appropriately to cues; make prompt decisions; and sustain vigilance (IOM, 1994; Mays, 1995).

The Committee on Optimization of Nutrient Composition of Military Rations for Short-Term, High-Stress Situations, an ad hoc committee of the CMNR, has been given the task of recommending the nutrient composition of a ration for combat missions to optimize physical and cognitive performance and to prevent adverse health consequences.

This daily ration is intended for repeated short-term use (three to seven days followed by one to three days of ad libitum recovery) by fit male soldiers during high-tempo, stressful combat missions. Stress may be caused by physical and cognitive workloads, extreme temperature, threats to safety, and sleep deprivation, all of which can interfere with cognitive performance (Lieberman et al., 2002b; Owen et al., 2004).

The purpose of this report is to briefly review relevant evidence on the effects of energy and macronutrients (i.e., carbohydrate, protein, and fat) on cognitive performance and mood, and to provide recommendations for the macronutrient composition of the assault ration, including types of each macronutrient, to enhance cognitive performance. Because factors associated with combat operations are likely to lead to cognitive deficits relative to normal functioning, the realistic goal in optimizing the nutrient composition of the ration should be to decrease these deficits, rather than to enhance performance beyond normal bounds.

To address this task this paper discusses the following specific questions:

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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  • Should the energy content of the ration (energy density) be maximized so as to minimize the energy debt, or is there a more optimal “mix” of macronutrients and micronutrients, not necessarily producing maximal energy density?

  • What would be the optimal macronutrient balance between carbohydrate, protein, and fat for such an assault ration to enhance cognitive performance during combat missions?

  • What are the types and levels of macronutrients (e.g., complex verses simple carbohydrates, proteins with specific amino acid profiles, type of fat, etc.) that would optimize such an assault ration to enhance cognitive performance during combat missions?

For the purpose of this paper, it has been assumed that other nutrional requirements of the soldiers (e.g., water, micronutrients) will be met. If these other requirements are not met, the results could override the importance of macronutrient requirements. For instance, it is well established that hypohydration (Wilson and Morley, 2003) and iron deficiency (Sandstead, 2000) present significant detriments to cognitive performance. In the combat situation, particularly during extreme temperatures, the highest priority for reducing cognitive impairment is adequate hydration (IOM, 1995).

The maximum weight of the macronutrient component of a 1,360 gram-ration is approximately 500 g [calculated from a standard, approximately 2,400-kcal ration, comprising 50 percent of energy as carbohydrate (300 g), 30 percent as fat (80 g), and 20 percent as protein (120 g)], with the remaining 860 g comprised of noncaloric components, including moisture, fiber, and micronutrients. Theoretically, 500 g could provide between 2,000 kcal (i.e., entirely protein and carbohydrate) and 4,500 kcal (i.e., entirely fat), in which case the energy needs of the soldiers (4,000 to 4,500 kcal/day) could be met within the weight limitation of the ration if energy density were increased as much as possible. The question is: Should the energy content of the ration be maximized, or is there a more optimal ratio of macronutrients for cognitive performance?

ENERGY INGESTION AND COGNITIVE PERFORMANCE

Acute Effects

The acute effects (hours) of energy ingestion on cognitive performance have been examined in a number of studies in healthy, nonstressed subjects. Several reviews of the literature have concluded that the provision of energy in the morning (breakfast) generally improves cognitive performance over the next 30 minutes to 2 h, compared with no energy provision, with more robust effects on tests of memory and less consistent effects on tests of attention or vigilance (Bellisle et al., 1998; Dye and Blundell, 2002; Kanarek, 1997; Leigh Gibson and

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Green, 2002; Pollitt and Matthews, 1998). The mechanism for these results has not been elucidated, but likely both gut-mediated and centrally acting postabsorptive signals are involved (Kaplan et al., 2001).

By contrast to the breakfast studies, large meals provided at mid-day (lunch) consistently impair cognitive performance (e.g., memory, vigilance, and reaction time) and mood (e.g., alertness and fatigue) over the next one to two hours, compared with the effects of those consuming no lunch or a light lunch. This phenomenon is known as the “post-lunch dip” and is likely related to normal changes in daily circadian rhythm as well as changes to habitual intake patterns (Bellisle et al., 1998; Dye et al., 2000; Kanarek, 1997; Leigh Gibson and Green, 2002).

A few studies have examined the short-term effects of energy intake on cognitive performance and mood under stressful conditions, showing the benefits of increased energy intake. One study found no changes in mood after low-energy intake during breakfast and lunch (264 kcal) as compared with a higher energy intake (1,723 kcal; consistent with energy needs of the subjects) during a nonstressful condition (Macht, 1996). However, when participants were subjected to emotionally stressful white noise, those with a low-energy intake experienced a degradation in mood (i.e., more irritability and less relaxation), whereas those with a higher energy intake did not.

Another study strongly supports a beneficial effect of increased energy ingestion on cognitive performance and mood under stressful conditions (Lieberman et al., 2002a). In this study, 143 male subjects from an elite combat unit were tested during periods of intense physical activity over 10 h, during which energy needs were not met with regular meals (approximately 765 kcal) (Lieberman et al., 2002a). Energy supplementation (carbohydrate-containing drink) throughout the day improved vigilance and mood (i.e., increased vigor, decreased confusion) in a dose-dependent manner compared with the effects of a noncaloric placebo drink. The strongest effects on performance resulted from the highest energy drink (approximately 1,309 kcal), followed by the medium-energy drink (approximately 654 kcal), and the placebo (0 kcal) (Figure B-9). It is impossible to determine from this study whether the beneficial effects were caused by an increase in energy ingestion or an increase in carbohydrate ingestion.

Medium-Term Effects

The medium-term effects (days) of dieting to lose weight consistently impair cognitive performance and mood (Leigh Gibson and Green, 2002). The effects are attributed to the act of dieting, rather than to inherent differences between dieters and nondieters because the impedence on performance is not observed when the same individuals are not dieting (Green and Rogers, 1995). It has been suggested that this impairment is caused more by a psychological pre-occupation with food and feelings of hunger than by a physiologic effect of low

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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FIGURE B-9 Vigilance performance of soldiers who received carbohydrate (CHO) beverages or placebo in addition to regular meals (providing approximately 765 kcal) while engaging in various activities over 10 h.

NOTE: A higher number on the y-axis represents improved performance.

SOURCE: Adapted from Lieberman et al. (2002a) with permission by the American Journal of Clinical Nutrition © Am J Clin Nutr. American Society for Clinical Nutrition.

energy intake (Leigh Gibson and Green, 2002). This conclusion is based on evidence that (1) individuals perform worse on cognitive tests when they are dieting, even when no actual weight is lost; (2) the magnitude and structure of the deficits is comparable to those caused by anxiety and depression; and (3) performance is not clearly affected by weight loss in the absence of other stress. It has been hypothesized that task-irrelevant feelings of hunger and thoughts of food may impair performance by interfering with normal working memory function. Working memory can be conceptualized as “the fundamental cognitive processing system, in that it serves to allocate limited cognitive processing capacity to other ongoing cognitive operations in order of their relevance or importance to an individual” (Leigh Gibson and Green, 2002).

A study using a similar eating pattern as would be consumed by combat soldiers (several days of hypocaloric intake followed by ad libitum intake) supports the hypothesis that energy restriction impedes performance in the absence of significant weight loss (Laessle et al., 1996). In this study, healthy female subjects consumed a low-calorie diet (approximately 651 kcal/day) for four days, followed by ad libitum intake (approximately 2,876 kcal/day) for three days each week for four weeks. During the low-calorie periods, subjects reported stronger feelings of hunger and thoughts about food as well as demonstrating

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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worse moods, more irritability, difficulties concentrating, and greater fatigue than during the ad libitum periods even though weight loss was minimal. Repeated episodes of low energy intakes over the 4 weeks did not reduce feelings of hunger. The implication of this study is that the negative effects of hunger are unlikely to be reduced during periods of low energy intake when soldiers repeatedly eat hypocaloric diets followed by ad libitum recovery periods. In other words, it may be very difficult to train soldiers to ignore their hunger feelings. It should be noted, however, that this study was performed with women and not under the unique added stressors of combat missions.

The hypothesis presented suggests that psychological feelings of hunger contribute to cognitive deficits during periods of low energy intake; however, the physiologic consequences of low energy intake and negative energy balance cannot be ruled out as contributing factors because other acute evidence (presented earlier) and longer term evidence under the stressful conditions presented below do not clearly indicate the mechanism involved. Most likely, both psychological and physiological factors associated with low energy intake, particularly under stressful conditions, contribute to the performance deficit.

The evidence that increased appetite interferes with the ability to perform optimally suggests that reducing hunger may be beneficial for mood and cognitive performance. Indeed, declining hunger sensations have been associated with being more energetic, lively, calm, and relaxed (Fischer et al., 2004). The macronutrient composition of foods can play an important role in minimizing hunger. Protein consistently and robustly induces greater satiety than carbohydrate or fat on a per calorie basis (Westerterp-Plantenga, 2003) and has a greater effect on satiety than do substantially higher energy intakes from the other macronutrients (Stubbs and Whybrow, 2004; Stubbs et al., 2000) (Figure B-10). Carbohydrate appears to induce greater satiety than fat does on a per calorie basis (Stubbs et al., 2000), but the differences are minimal when palatability and energy density of foods are matched (Rolls and Bell, 1999). Thus, to reduce the negative effects of hunger on cognitive performance and mood, it may be beneficial to increase the protein content of hypocaloric military rations and to reduce the fat content.

Various types of each macronutrient also have different effects on satiety (Stubbs et al., 2000). A review concluded that high glycemic index carbohydrates (i.e., rapidly raise blood glucose concentration) have a greater effect on satiety than low glycemic index carbohydrates over the short term (up to one hour after carbohydrate ingestion), whereas lower glycemic index carbohydrates have a stronger effect on satiety over the longer term (i.e., up to 6 h after carbohydrate ingestion) (Anderson and Woodend, 2003). However, these effects are not likely caused entirely by changes in blood glucose (Kaplan and Greenwood, 2002). The data implicating different effects of fat type on satiety are mixed, with some suggesting that polyunsaturated fatty acids have a stronger effect on increasing satiety than monounsaturated or saturated fatty acids do (French and Robinson, 2003; Lawton et al., 2000), whereas others have found no differences between

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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FIGURE B-10 Effect of increasing energy content of macronutrient loads on satiety over 3.25 h.

NOTE: Data were collated from a number of studies.

SOURCE: Adapted from Stubbs and Whybrow (2004).

the two (Alfenas and Mattes, 2003; Flint et al., 2003). Medium-chain triglycerides, which are rapidly metabolized, have been shown to exert a stronger effect on satiety than long-chain triglycerides do; however, only a few human studies are available and the results are inconclusive (French and Robinson, 2003; St-Onge and Jones, 2002). Research on the effects of protein type on satiety is also limited because evidence in human studies suggesting that some proteins might suppress appetite more than others is inconsistent (Anderson and Moore, 2004; Westerterp-Plantenga, 2003).

It is important to note that, although it is argued here that reducing hunger in soldiers consuming hypocaloric rations may be beneficial for cognitive performance, this may not be relevant if appetite is suppressed by hypohydration, physical activity, or stress to the extent that feelings of hunger and thoughts of food are eliminated. It is well documented that soldiers tend to underconsume foods, and this may be partially due to a suppression of appetite (IOM, 1995). Thus, it is important to determine whether the expected increase in appetite

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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associated with the hypocaloric intake of combat soldiers is stronger or weaker than the suppression of appetite that will be caused by other factors. There is evidence, however, that when military rations provide only 60 percent of energy needs (i.e., energy intake and energy expenditure was 1,946 kcal and 3,200–3,300 kcal, respectively), the entire rations are consumed (Shukitt-Hale et al., 1997), suggesting that soldiers’ appetites are strong under these circumstances. These data would support the argument that strong feelings of hunger will be present in combat soldiers consuming assault rations containing approximately 2,400 kcal/day when their needs are > 4,000 kcal/day.

Long-Term Effects

The long-term effects (weeks or months) of energy intake on cognitive performance are not relevant if soldiers are able to consume enough excess energy during the one- to- three-day ad libitum recovery period to make up for the negative energy balance during the three to seven days, such that they do not lose weight. By contrast, if soldiers are in a state of negative energy balance over weeks and months because of repeated consumption of hypocaloric diets and inadequate recovery periods, then the long-term effects of low energy intake are relevant.

Evidence on the long-term effects of low energy intake on cognitive performance shows that those effects are minimal in the absence of significant stress but are significant if stress is present. In a review of the effects of underconsumption of military rations on cognitive performance, Mays (1995) concluded that underconsumption leading to weight loss up to 6 percent over 10 to 45 days does not affect performance in the absence of significant stress. A more recent study over a 30-day trial supports this conclusion (Shukitt-Hale et al., 1997). However, consistent with the long-term dieting data (e.g., Kretsch et al., 1997), underconsumption combined with stress during military operations (e.g., exercise, sleep deprivation, and danger) significantly degrades performance within a few days (Mays, 1995). Based on the available data, Mays proposed a relationship between long-term negative energy balance and cognitive performance (Figure B-11). These data suggest that consumption levels of 75 to 90 percent of requirements may actually enhance performance in the first 3 to 15 days, whereas consumption of 50 percent or less of requirements degrades performance, particularly under stressful conditions. Over the longer term, performance continues to degrade along with negative energy balance. Thus, if repeated short-term periods of low energy intake during combat operations lead to long-term negative energy balance, deficits in cognitive performance can be expected.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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FIGURE B-11 Proposed relationship between energy intake as a percentage of energy expenditure and cognitive performance over two months, based on the results of several studies.

SOURCE: Adapted from Mays (1995).

CARBOHYDRATE INGESTION AND COGNITIVE PERFORMANCE

Glucose Compared with a Noncaloric Placebo

For the purposes of this paper, “carbohydrate” refers to digestible or glycemic carbohydrates that provide energy (primarily sugars and starches). It does not include dietary fiber, resistant starch, or other nondigestible carbohydrates that do not provide energy as a carbohydrate.

A large number of studies conducted over the past 20 years have shown beneficial effects of glucose ingestion on cognitive performance as compared with noncaloric sweetened placebos (e.g., aspartame, saccharin) in animals and humans over the short term—from 15 minutes to 3 h after ingestion (Greenwood, 2003; Korol, 2002; Korol and Gold, 1998; Messier, 2004). Cognitive impairments associated with hypoglycemic episodes have also been a consistent finding

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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(McCall, 1992). Early studies suggested that the cognitive-enhancing effects of glucose were only evident when an existing deficit was present, such as in elderly subjects and in patients with Alzheimer’s disease, schizophrenia, and Down syndrome, but not in healthy young adults (Korol and Gold, 1998). Since that time, others have shown that consuming glucose can improve performance in young adults if cognitive tasks are sufficiently demanding (Benton, 2001); however, the magnitude of the effects depends on glucose regulation and baseline cognitive abilities (Awad et al., 2002; Greenwood, 2003; Kaplan et al., 2000; Messier, 2004).

The beneficial effects of consuming glucose are dependent on the type of cognitive test, task difficulty, and glucose dose (Greenwood, 2003; Messier, 2004). In contrast with the data showing the benefits of eating breakfast and the detriments of eating lunch, the effects of consuming glucose appear to be positive in both the morning and the afternoon (Sunram-Lea et al., 2001). The effects of glucose are strongest on functions mediated by the medial temporal lobe and surrounding areas, including long-term verbal memory, and less robust for other tasks, including short-term memory, attention, and reaction time. Glucose consumption can, however, improve performance on a wide range of tasks as long as the tasks are of sufficient difficulty. For instance, Kennedy and Scholey (2000) found glucose ingestion improved performance in young adults on a difficult test (serial sevens, which requires subjects to count backwards by sevens), but not on two easier tests (Figure B-12). These findings suggest that an increased brain requirement for glucose is needed before benefits of glucose ingestion can be observed. Conditions for which glucose could reverse deficits in performance caused by increased brain requirements for glucose include those of aging (McNay and Gold, 2001), increased cognitive demand (Fairclough and Houston, 2004), and physical activity (Brun et al., 2001; Grego et al., 2004; Nybo and Secher, 2004). Thus, carbohydrate ingestion is likely to benefit cognitive performance during combat operations for which brain glucose requirements would likely be increased because of the demanding nature of the tasks and high levels of physical activity.

The dose of glucose that enhances cognitive performance follows an inverted U-shaped response in humans and animals. Consistently, low doses have no effect on performance, intermediate doses (25 to 75 g) improve performance, and high doses have no effect or impair performance (Greenwood, 2003; Greenwood et al., 2003; Messier, 2004; Parsons and Gold, 1992) (Figure B-13). Taken together, these findings suggest that a moderate amount of glucose improves performance on a range of demanding cognitive tests in young adults, or on tasks in demanding situations (e.g., stress, physical activity), but glucose is unlikely to improve performance on simpler tasks under nonstressful conditions.

There is no consensus on the mechanism that explains the effects of glucose on cognitive performance, but several hypotheses have been proposed. The following effects of glucose ingestion have been most commonly suggested as

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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FIGURE B-12 Mean number of responses (subtractions or words produced) made on each of three tasks after ingestion of noncaloric saccharin-sweetened placebo or of 25 g glucose drinks.

*p < 0.01 compared with corresponding placebo group.

SOURCE: Adapted from Kennedy and Scholey (2000).

possible mechanisms: replenishes brain extracellular glucose that declines during difficult tasks; increases synthesis of the brain neurotransmitter acetylcholine; increases central insulin; or influences peripheral signals that are relayed to the brain via the vagus nerve (Greenwood, 2003; Messier, 2004; Park, 2001).

Carbohydrate Foods

As noted earlier, one study found that a carbohydrate-containing beverage provided in addition to regular hypocaloric meals benefited vigilance and mood during combat training (Figure B-9), but it is impossible to determine whether the benefits were due to increased energy intake or to carbohydrate intake (Lieberman et al., 2002a). The authors suggested that the benefits could have been due to an increased supply of glucose to the brain, which could have helped

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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FIGURE B-13 Logical memory scores in elderly subjects 5 and 40 minutes after glucose ingestion, presented as differences from placebo (saccharin). Significant memory enhancement was observed after 25 g glucose, but not at the higher or lower doses.

* p < 0.05 versus placebo.

SOURCE: Adapted from Parsons and Gold (1992), used with permission from Elsevier.

prevent a reduction in the synthesis of neurotransmitters protecting the brain from the consequences of an energy deficit.

Other studies suggest that carbohydrate, independent of energy intake, benefits performance under hypocaloric (Wing et al., 1995) and physically demanding (Achten et al., 2004) circumstances that are relevant for combat operations. Wing and colleagues (1995) found that a low-energy (549 kcal/day), low-carbohydrate–high-fat diet was associated with impaired performance on a test of general brain function after one week as compared with the results of an equal-energy, high-carbohydrate–low-fat diet. In addition, during 11 days of intense running training, Achten and colleagues (2004) found that higher carbohydrate–lower fat diets improved overall mood and reduced fatigue as compared with the results of equal-energy (approximately 3,900 kcal/day), low-carbohydrate–high-fat diets.

Under nonexercise, adequate energy situations, carbohydrate ingestion has been associated with both better and worse moods (Benton, 2002; Leigh Gibson and Green, 2002), which may be dependent on the testing time after ingestion. Carbohydrate may improve mood up to 30 minutes after ingestion, but it is

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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associated with a sedative effect after about 2 h (Benton, 2002). The sedating effect may be caused by a carbohydrate-induced increased tryptophan/large neutral amino acid ratio, which increases both the brain tryptophan levels and the synthesis of the neurotransmitter serotonin (Spring et al., 1994). However, the effect of carbohydrate on serotonin is abolished with the ingestion of as little as 4-percent protein (Benton, 2002; Benton and Donohoe, 1999; Benton and Nabb, 2003; Spring et al., 1994), so these findings are likely not relevant for military rations with mixed macronutrient composition. Another hypothesis suggests that beneficial effects of carbohydrate on mood are related to an increased release of endorphins relevant to the ingestion of any palatable food, rather than to carbohydrate per se (Benton, 2002).

Carbohydrate Type

The type of carbohydrate may be important for cognitive performance although research in this area is limited to two studies. In one study in healthy elderly subjects, 50 g of carbohydrate from glucose, potato (high glycemic index), or barley (low glycemic index) all improved performance on memory and a test of general brain function up to one hour after ingestion, particularly in subjects with poorer baseline memory and glucose regulation (Kaplan et al., 2000). The cognitive-enhancing effects of barley, which raised blood glucose to 6 mmol/L, were novel because it had previously been believed that blood glucose must be at a concentration of 8 to 10 mmol/L for a benefit to be observed. These findings were supported by a recent study that found that a high-carbohydrate meal with a lower glycemic index improved memory in young adults up to 3 h after ingestion, but a higher glycemic index meal did not (Benton et al., 2003). The findings could not be related to blood glucose levels, but these data, along with the evidence showing an inverted U-shaped dose response for glucose, suggest that a prolonged increase in blood glucose and insulin levels, rather than rapid fluctuations, may be beneficial.

It is noteworthy that virtually all studies examining the effects of carbohydrate on cognitive performance or mood have used glucose or glucose polymers (e.g., starches). A few studies have examined the effects of fructose which is metabolized differently from glucose, in rats, but the evidence is mixed (Messier, 2004). Until evidence to the contrary is available in humans, it should be assumed that the beneficial effects of carbohydrate are limited to sources of glucose or glucose polymers.

PROTEIN, FAT, MACRONUTRIENT BALANCE, AND COGNITIVE PERFORMANCE

Protein has the potential to influence cognitive performance because several amino acids, including tryptophan, tyrosine, phenylalanine, arginine, histadine,

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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and threonine, are precursors of neurotransmitters or neuromodulators and can influence their synthesis (Lieberman, 2003). Indeed, individual amino acids have been shown to influence cognitive performance; however, these effects are likely not relevant when examining the effects of protein consumed as part of a food ration (Greenwood, 1994). In particular, tyrosine benefits cognitive performance in sleep deprived, stressed subjects, likely by its role as a precursor for the neurotransmitters norepinephrine and dopamine (Lieberman, 2003). Tryptophan may be beneficial as a sleep aid, by way of its effects on increasing synthesis of serotonin, and it improves vigilance by way of increasing the release of melatonin (Lieberman, 2003). However, any potential benefits of these amino acids would likely be as between-meal supplements, rather than as part of normal meals (Greenwood, 1994).

As noted in the carbohydrate section above, several reports have concluded that high-carbohydrate–low-protein meals are sedating because they cause an increase in serotonin synthesis, whereas protein-rich meals are arousing and can improve reaction time and vigilance (Dye and Blundell, 2002; IOM, 1994; Leigh Gibson and Green, 2002). However, as noted, these findings are likely not relevant for mixed macronutrient military rations because as little as 4 percent protein prevents the effect on serotonin. Moreover, other data do not support a negative influence on mood by consumption of a high-carbohydrate–low-protein diet. A review by Benton and Donohoe (1999) concluded that diets higher in carbohydrate and lower in protein are associated with less depression, anger, and tension and with being more energetic.

Although the fat content of diets can have an effect on cognitive performance over the long term (i.e., months or years) (Greenwood and Young, 2001; Kaplan and Greenwood, 1998), fat likely only has limited effects over the short term (i.e., hours or days), possibly related to the fact that rates of fat and carbohydrate oxidation are not influenced by the fat content of a meal (Flatt et al., 1985). Nevertheless, some studies have found acute effects of fat on performance and mood, but the data are inconsistent. Recent reviews concluded that in general, high-fat–low-carbohydrate meals can lead to declines in alertness and reaction time, particularly when they differ from habitual fat intake (Dye and Blundell, 2002; Leigh Gibson and Green, 2002).

Few direct comparisons between pure macronutrients have been made. Kaplan and colleagues (2001) found that in healthy elderly persons, pure protein, carbohydrate, and fat could all improve memory performance 15 minutes after ingestion compared with a noncaloric placebo, suggesting a general benefit of energy ingestion, likely mediated by a peripheral mechanism, which could include gut peptides or signals to the brain by way of the vagus nerve. However, it was also found that each macronutrient had unique effects on performance. For instance, as shown in Figure B-14, only glucose tended to improve memory 60 minutes after ingestion, and performance on a visual-motor task; and protein was the only macronutrient to slow the rate of forgetting. Various peripheral and

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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FIGURE B-14 (A) Mean (± standard error of means) scores on immediate and delayed paragraph recall 15 and 60 minutes after consumption of placebo, glucose, fat, and protein test drinks. (B) Mean (± standard error of means) scores on Trail Making Test (parts A + B) in men (n = 10) at 15 and 60 minutes after ingestion of placebo, glucose, fat, and protein test drinks.

NOTE: Lower scores represent better performance. (A) a, b, c, d, e = significantly different from placebo: a = p ≤ 0.02; b = p for trend = 0.04; c = p ≤ 0.001; d = p = 0.002 (rate of forgetting, immediate + delayed); e = p for trend = 0.09 (for composite score, immediate + delayed). (B) f, g = significantly different from placebo; f = p for trend = 0.04; g = p = 0.02.

SOURCE: Adapted from Kaplan et al. (2001) with permission by the American Journal of Clinical Nutrition © Am J Clin Nutr. American Society for Clinical Nutrition.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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central mechanisms could account for these specific effects. Another study also found unique effects of each macronutrient in healthy young adults (Fischer et al., 2001). Carbohydrate improved choice reaction and short-term memory time after one hour; protein improved choice reaction time after two hours; fat improved performance on short-term memory and attention.

Taken together, several reviews have concluded that, although macronutrients have been shown to have different effects on cognitive performance, the effects have been inconsistent, and few overall conclusions can be made at this time about an optimal ratio of macronutrients for cognitive performance (Bellisle et al., 1998; Dye and Blundell, 2002; Dye et al., 2000; Kanarek, 1997; Lieberman, 2003).

CONCLUSIONS

Despite discrepancies in the literature, some conclusions can be made about the effects of energy ingestion on cognitive performance. (1) Energy ingestion approaching the level of energy needs generally improves cognitive performance and mood over the short term (several hours) compared with no energy or very low energy ingestion; the fact that benefits seem to be independent of weight loss suggest that feelings of hunger and thoughts of food contribute to the cognitive and mood deficits. Thus, minimizing hunger may minimize the negative effects on performance. Hunger can be minimized with higher protein and lower fat ingestion. (3) Over longer periods (weeks or months), there is a gradual impairment in cognitive performance associated with negative energy balance and weight loss, with greater and more rapid deficits associated with very low energy intakes (< 50 percent of energy requirements), particularly under stressful conditions.

The review of the research presented in this paper shows that the scientific literature in this area is inconsistant and contradictory; therefore, it is difficult to make definitive recommendations regarding the questions posed in the introduction. The research, although not conclusive, supports the following conclusions described below.

The following are desired characteristics of an assault ration designed for cognitive performance:

  • Adequate and sustained glucose supply to the brain. The provision of glucose or carbohydrate to the brain improves mood and performance when brain glucose requirements increase, which appears to occur during cognitively demanding tasks, particularly under hypocaloric, stressful, or physically demanding conditions.

  • Moderate fluctuations in blood glucose. Consistent evidence shows that both hypoglycemia and hyperglycemia impair cognitive performance; that intermediate, but not high or low, doses of glucose improve performance;

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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and that limited evidence shows that low glycemic index carbohydrates improve performance over a longer period than do higher glycemic index carbohydrates. Thus moderate, rather than extreme, fluctuations in blood glucose are desirable.

  • Minimize feelings of hunger. Hypocaloric intakes are associated with deficits in cognitive performance and mood, and this is caused, in part, by feelings of hunger and thoughts of food interfering with normal cognitive processes. Reducing feelings of hunger is desirable.

  • Minimize long-term negative energy balance. Sufficient data indicate that long-term energy deficits resulting in negative energy balance and weight loss are associated with deficits in cognitive performance and mood under stressful situations. Long-term negative energy balance should be minimized.

The optimal composition of the assault ration for cognitive performance would be characterized by the following:

  • A maximized carbohydrate content of the ration to provide an adequate and sustained supply of glucose to the brain, because of their hypocaloric nature and the fact that substantial carbohydrate will be required to sustain physical activity. The carbohydrate source should ideally provide glucose (e.g., glucose, sucrose, starch) rather than other monosaccharides (e.g., fructose) as the beneficial effects of carbohydrate have only been shown with glucose. The effect of the ration on blood glucose should be moderate for optimal and sustained cognitive performance and should also reduce feelings of hunger. Importantly, the carbohydrate source may have a high or low glycemic index to give the overall ration a moderate effect on blood glucose, because the other components of the ration could affect blood glucose. For instance, both protein (increases insulin release) and fiber can lower blood glucose. Higher protein and fiber content rations may necessitate higher glycemic index carbohydrates to obtain a ration with a moderate effect on blood glucose.

  • If feelings of hunger are strong and long-term energy balance is not a major problem (i.e., energy balance can be maintained by high energy intakes during the recovery periods between combat operations), then protein content of the ration should be increased and fat content should be decreased to increase satiety and reduce feelings of hunger. In this case, the energy density of the ration will not be maximized. Not enough evidence exists to recommend a specific amino acid or fatty acid profile that will optimize cognitive performance compared with any other profile. It seems prudent to supply minimum amino acid requirements.

  • If feelings of hunger are weak because of stress or hypohydration out-weighing the effects on appetite of the low calorie diet, and long-term

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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negative energy balance and weight loss are expected, then minimum protein requirements should be met for nitrogen balance, and fat content should be increased to maximize energy intake over the long term. In this case, additional protein to reduce hunger would be less important than increasing long-term energy intake by maximizing fat content and energy density of the ration.

  • To reduce long-term negative energy balance, high-energy intake should be encouraged during the recovery periods. Thus, intake during recovery should consist of energy-dense foods with minimal effects on satiety (i.e., high-fat, low-protein foods).

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Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Do Structured Lipids Offer Advantages for Negative Energy Balance Stress Conditions?

R. J. Jandacek, University of Cincinnati

INTRODUCTION AND REVIEW

The objective of this paper is to address the question of whether structured lipids offer advantages as a source of energy for hypocaloric, high-energy expenditure stress conditions of short-term combat operations (repetitive three- to seven-day missions with recovery periods of one to three days). A review of structured lipids and their metabolism is followed by a discussion of the question provided and the recommendation.

Ingested Energy Sources

Virtually all of the fat that we consume is in the form of triacylglcyerols, three long-chain fatty acids bonded to glycerol. The chain length of most dietary fatty acids is 16 and 18 carbon atoms.

It was found by Rubner (1885) and Atwater and Bryant (1900) that the energy in food that is available to support metabolic and other activity is equivalent to that produced by oxidation of the carbon and hydrogen atoms of the compounds in food macronutrients. In a bomb calorimeter, the oxidation of carbohydrates generates 4 kcal/g (16.7 kJ/g). The oxidation of fatty acids with 18-carbon chains yields 9.5 kcal/g (39.7 kJ/g). Fatty acids of shorter chain length contain a higher fraction of carbon atoms bonded to oxygen and therefore give off less energy when oxidized. Heat produced by the oxidation of octanoic acid is 8 kcal/g (33.4 kJ/g).

Although we have understood this concept for a century, the equivalence of the bomb calorimeter and the human body is a remarkable discovery. The β-oxidation of palmitic acid that produces acetyl CoA and carbon dioxide (CO2) via the TCA (tricarboxylic acid) cycle provides the same amount of heat and work as the bomb calorimeter. The sum of the reactions in the body is the same as that in the bomb calorimeter: fat plus oxygen produces heat, CO2, and water.

The chemical energy contained in the C-C and C-H bonds of fatty acids is the densest source of energy available in foods, where C is carbon and H is hydrogen. The energy of ingested fat is stored if total caloric intake exceeds energy expenditure, or it is used to meet energy needs. The sections that follow briefly review the types of dietary fat and the unique properties of fats made with medium-chain fatty acids.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Types of Dietary Fat

Dietary fat comprises triacylglycerols, phospholipids, and sterols. Phospholipids and sterols are important in health, but triacylglycerols provide essentially all of the energy in dietary lipids.

A triacylglycerol molecule contains an asymmetric carbon atom (carbon 2 of the glycerol) if the fatty acids in the 1 and 3 positions are different. Fatty acid positions in the 1 and 3 positions are hydrolyzed by pancreatic lipase. The chemical structure of a triacylglycerol molecule (trilaurin) is shown in Figure B-15.

Figure B-16 shows dietary fatty acids in animal and vegetable triacylglycerols. The long-chain fatty acids account for a majority of the fat consumed by people. Docosahexaenoic acid is found in fatty fish such as salmon and tuna.

Medium-Chain Fatty Acids and Structured Lipids

In addition to these long-chain fatty acids in common foods, small quantities of shorter fatty acids are part of the triacylglycerols of butterfat. These fatty acids include butyric, hexanoic (caproic), octanoic (caprylic), decanoic (capric), and dodecanoic (lauric) acids. Octanoic and decanoic acids make up approximately 4 percent of butterfat fatty acids.

Octanoic and decanoic acids account for approximately 13 percent of the fatty acids in coconut oil. They became commercially available as byproducts of coconut oil fractionation to obtain lauric acid, an ingredient for detergent products. These byproducts made it possible to synthesize medium-chain fatty acid triacylglycerols (MCT, MCT oil).

FIGURE B-15 A triacylglycerol, trilaurin (C39H74O6).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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FIGURE B-16 Principal long-chain fatty acids found in dietary fat. Octanoic acid is a medium-chain fatty acid that is a principal component of structured lipids.

Structure

Synthetic triacylglycerols were also made from mixtures of long-chain and medium-chain fatty acids; these esters were termed “structured lipids,” even though the fatty acid distribution in the three positions of the glycerol was completely random and unstructured. More recently, enzymatic techniques have made it possible to synthesize triacylglycerols with medium-chain fatty acids in the 1 and 3 positions, and long-chain fatty acids in the 2 position.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Absorption

MCT oil was found to have therapeutic advantages in cases of pancreatic insufficiency because its intestinal hydrolysis is more rapid than that of long-chain fats. MCT oil is absorbed from the intestine in subjects with subnormal pancreatic lipase, such as patients with cystic fibrosis. The hydrolysis products are transported via the portal vein rather than via the lymphatic route. MCT does not provide the essential fatty acids linoleic and α-linolenic acids.

Utilization

Structured lipids were proposed to have benefits in providing energy to patients who were not able to consume food through the gastrointestinal tract and therefore required intravenous nutritional support (i.e., total parenteral nutrition, TPN). The provision of intravenous energy has successfully used emulsions of fat in small particles. It was found that these particles in blood circulation acquire surface lipoproteins (e.g., apolipoprotein C-II, C-III, E) from high-density lipoproteins. The lipid is hydrolyzed by endothelial lipoprotein lipase and the lipolytic products are used by peripheral tissues.

Medium-chain fatty acids are rapidly hydrolyzed from triacylglycerol and do not require carnitine for tissue uptake; however, acidosis can result from this high rate of hydrolysis. For this reason, physical mixtures of MCTs or structured lipids with medium-chain fatty acids and long-chain fatty acids (including essential fatty acids) bonded to the same glycerol molecule may have advantages for TPN compared with long-chain triacylglycerols (Bellantone et al., 1999; Rubin et al., 2000). Some reported advantages of structured lipids in TPN were summarized previously (Jandacek, 1994).

In addition to use in TPN, another hypothetical nutritional advantage for medium-chain fatty acids (and therefore for structured lipids) was explored. This hypothesis suggests that the rapid absorption of medium-chain fatty acids via the portal vein to the liver results in rapid mitochondrial oxidation of these acids that can then reduce the body’s use of glycogen as a fuel. It was also suggested that the use of MCTs in place of carbohydrate would reduce insulin elevation and hypoglycemia. As reviewed previously (Jandacek, 1994), studies did not support these hypotheses in human exercise trials, and a more recent trial also found no performance improvement with a specific structured lipid (Vistisen et al., 2003).

A further refinement to structured lipids was the synthesis of “truly structured” lipids, in which the positions of the medium- and long-chain fatty acids were specific rather than random. The advantage of this kind of structure is that the placement of the medium-chain fatty acids in the exterior 1 and 3 positions would result in their rapid lipase-catalyzed hydrolysis (Jandacek et al., 1987). Specific position structured lipids would be capable of providing essential fatty acids (in the 2 position) with rapidly hydrolyzed octanoic or decanoic acid in the

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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1 and 3 positions. This kind of molecule could therefore be advantageous in providing fat in patients with pancreatic insufficiency.

The isomerization of monoacylglycerols may affect the metabolism of structured lipids. The preferred (low energy) form of monoacylglycerols is the 1(3)-monoacylglycerol. Isomerization of the 2-monoacylglycerol to the 1(3) isomer is accelerated by heat is rapid for short- and medium-chain fatty acids and for long-chain polyunsaturated fatty acids. It is likely that a significant fraction of 2-monoacylglycerols of medium-chain fatty acids formed in the intestine is isomerized (and then hydrolyzed) within the time frame of intestinal transit. A comparison of the absorption of long-chain fatty acid triacylglycerols, MCTs, and structured lipids is shown in Figure B-17. The structured lipid is shown as a “specific” triacylglycerol.

DISCUSSION OF QUESTIONS

Based on the physical properties and metabolism of structured fatty acids, three areas of discussion address the question of whether or not structured lipids have any of the following advantages in energy deficit status during high stress circunstances: (1) intestinal absorption, (2) energy content, (3) energy utilization, and (4) appetite.

Is There an Advantage in Intestinal Absorption?

Current data indicate that there is no advantage in the absorption of medium-chain fatty acids in structured lipids, as long as the subjects have normal levels of pancreatic lipase. There is no need to optimize the hydrolysis rate in the small intestine of normal healthy individuals. There is a 20-fold excess capacity for the absorption of fat, suggesting that there are more than adequate levels of lipase, bile salts, enterocyte capacity, and chylomicron formation. Evidence for this is supported by the work of Kinsell and colleagues (1953). They fed vegetable oil as the entire diet to subjects for a week and observed not only that there were no ill effects, but also that there were reductions in serum cholesterol. Work by Kasper (1970) found that when dietary fat was raised to three times the normal consumption at a level of 300 g/day, the body was able to compensate, and this level of fat was well absorbed. He then pushed the system further with a diet of 639 g fat/day. This amount also was well tolerated by a subject during a 20-day trial, further confirming that normal humans have an excess capacity for the absorption of fat. These results negate the need to optimize the hydrolysis rate in the small intestine of healthy individuals. Furthermore, there is no evidence that subjects stressed by several days of caloric deficit will absorb less than normal levels of dietary fat. The use of a fat that is hydrolyzed rapidly will therefore not enhance caloric use relative to normal, well-absorbed, long-chain fats in people with normal pancreatic lipase levels.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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FIGURE B-17 Intestinal absorption of triacylglcyerols of long- and medium-chain fatty acids.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×
Is There an Advantage in Energy Content?

As discussed above, the maximum energy content of macronutrients available to a person is the heat of combustion. For long-chain fats this value is 9.5 kcal (39.7 kJ)/g. The caloric energy of the fatty acids is dependent on chain length, and the energy that can be used from octanoic acid is 8 kcal (33.5 kJ)/g. Although the difference in caloric density of long-chain and medium-chain fatty acids is small, it seems prudent to maximize the energy provided per unit weight of the food provided in anticipated caloric deprivation.

Is There an Advantage in Energy Utilization?

The energy provided by macronutrient metabolism results in storage, work, or heat. In the case of excessive caloric intake, a portion of the energy is directed toward storage, principally in the form of triacylglycerol fatty acids in adipose tissue. In negative caloric balance, ingested energy is converted to heat and work. In a situation of energy stress in a high-temperature environment, it would be desirable to maximize ingested energy as work (ATP production).

A study of high relevance to this topic was reported by Bendixen and coworkers (2002). They compared four types of triacylglycerol fats in 11 normal, healthy men ranging in age from 22 to 28 years. The fats included a conventional long-chain triacylglcyerol; a positionally specific structured fat (octanoic acid in the 1(3) position); a randomly structured lipid; and a mixture of MCT with long-chain triacylglycerols. All three fats that included medium-chain fatty acids resulted in higher postprandial energy expenditure than did the long-chain dietary fat. This result is consistent with rapid absorption of medium-chain fatty acids via the portal vein and, because elongation is not favored, they are directed toward mitochondrial oxidation. If this oxidation is not entirely coupled to the production of ATP (e.g., peroxisomal oxidation) then the result would be a negative energy balance. In this study there was no difference among fats in subjective appetite measures or ad libitum energy consumption. Total energy expenditure was smaller after the conventional fat meal, relative to the other fats. Diet-induced thermogenesis was lower after the conventional fat than after the random structured lipid. In the 5-hour postprandial period there was a (nonsignificant) trend toward lower oxidation of fat from the long-chain fat (1.65 g/5 h versus 3.1–3.5 g/5 h), and a trend toward higher carbohydrate oxidation in this group (13.9 versus 11.1–13.1 g/5 h). The authors concluded that “structured fats do not change short-term postprandial appetite sensations or ad libitum energy intakes, but do result in higher postprandial energy expenditure than do conventional fats and hence promote negative energy and fat balance” (Bendixen et al., 2002).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Is There an Advantage in Appetite?

During hypocaloric stress it is possible that a nutrient that provides satiety would be advantageous. There was no difference in the satiating effect of the different fats in the Bendixen study in terms of subjective tests and in terms of ad libitum caloric intake (Bendixen et al., 2002). However, in some reports long-chain fatty acids have been reported to be more satiating than medium-chain fatty acids (Cox et al., 2004; Feltrin et al., 2004).

CONCLUSION

There is no reason to substitute structured lipids for long-chain fatty acid triacylglycerols to meet the needs of stress resulting from high energy expenditure and low energy intake. Maximizing caloric density is the optimal approach. During a relatively short duration of five to ten days, essential fatty acids are not limiting factors. In terms of the fat composition, triacylglycerols that are oxidatively stable, high in energy density, and readily digested are recommended. Oils high in oleic acid and low in polyunsaturated acids (e.g., high oleic oils from cultivars of sunflower and safflower oils) meet these criteria.

REFERENCES

Atwater WO, Bryant AP. 1900. The availability and fuel value of food materials. Connecticut Storrs Agricultural Extension Station Annual Report, 1899. Pp. 73–110.


Bellantone R, Bossola M, Carriero C, Malerba M, Nucera P, Ratto C, Crucitti P, Pacelli F, Doglietto GB, Crucitti F. 1999. Structured versus long-chain triglycerides: A safety, tolerance, and efficacy randomized study in colorectal surgical patients. J Parenter Enteral Nutr 23(3):123–127.

Bendixen H, Flint A, Raben A, Hoy CE, Mu H, Xu X, Bartels EM, Astrup A. 2002. Effect of 3 modified fats and a convential fat on appetite, energy intake, energy expenditure, and substrate oxidation in healthy men. Am J Clin Nutr 75(1):47–56.


Cox JE, Kelm GR, Meller ST, Randich A. 2004. Suppression of food intake by GI fatty acid infusions: Roles of celiac vagal afferents and cholecystokinin. Physiol Behav 82(1):27–33.


Feltrin KL, Little TJ, Meyer JH, Horowitz M, Smout AJ, Wishart J, Pilichiewicz AN, Rades T, Chapman IM, Feinle-Bisset C. 2004. Effects of intraduodenal fatty acids on appetite, antropyloroduodenal motility, and plasma CCK and GLP-1 in humans vary with their chain length. Am J Physiol Regul Integr Comp Physiol 287(3):R524–R533.


Jandacek RJ. 1994. Structured lipids: An overview and comments on performance enhancement potential. In: Marriott BM, ed. Food Components to Enhance Performance. Washington, DC: National Academy Press. Pp. 351–379.

Jandacek RJ, Whiteside JA, Holcombe BN, Volpenhein RA, Taulbee JD. 1987. The rapid hydrolysis and efficient absorption of triglycerides with octanoic acid in the 1 and 3 positions and long-chain fatty acid in the 2 position. Am J Clin Nutr 45(5):940–945.


Kasper H. 1970. Faecal fat excretion, diarrhea, and subjective complaints with highly dosed oral fat intake. Digestion 3(6):321–330.

Kinsell LW, Michaels GD, Partridge FW, Boling LA, Balch HE, Cochrane GC. 1953. Effect upon serum cholesterol and phospholipids of diets containing large amounts of vegetable fat. Am J Clin Nutr 1(3):224–231.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Rubin M, Moser A, Vaserberg N, Greig F, Levy Y, Spivak H, Ziv Y, Lelcuk S. 2000. Structured triacylglycerol emulsion, containing both medium- and long-chain fatty acids, in long-term home parenteral nutrition: A double-blind randomized cross-over study. Nutrition 16(2):95–100.

Rubner M. 1885. Calorimetrische Untersuchungen. Zeitsch Biol 21:377.


Vistisen B, Nybo L, Xu X, Hoy CE, Kiens B. 2003. Minor amounts of plasma medium-chain fatty acids and no improved time trial performance after consuming lipids. J Appl Physiol 95(6):2434–2443.

Optimum Protein Intake in Hypocaloric States

L. John Hoffer, Jewish General Hospital

INTRODUCTION

The goal of this workshop is to advise the military in developing a hypocaloric ration that maximizes physical and mental performance. As currently envisioned, rations of 2,400 kcal per day will be consumed by soldiers expending approximately 4,000 to 4,500 kcal per day for three to seven days followed by one to three days of recovery. What is the optimum protein content of such a ration? Should the energy deficit be minimized, or are other aspects of the ration more important?

The main concerns when a person’s energy expenditure consistently exceeds intake—that is, when he or she is starving—are depletion of the fat store and loss of muscle mass and function. The 32 young men who participated in the famous Minnesota human starvation experiment (Keys et al., 1950) consumed approximately 1,500 kcal per day and, during the subsequent 26 weeks, they lost approximately 25 percent of their lean tissue mass. This occurred despite their consumption of 50 g of protein per day, an amount that exceeded the average protein requirement of 0.6 g/kg of body weight and was close to the current Recommended Dietary Allowance (RDA) of 0.8 g/kg (IOM, 2002). By the 24th week of the study, physiologic adaptation had restored energy and nitrogen equilibrium despite continuing starvation. This adaptation is crucial for survival during starvation (Hoffer, 1999a, b).

The Minnesota experiment illustrates what has long been known (Elwyn et al., 1979; Munro, 1964; Pellett and Young, 1992) and recently reemphasized (IOM, 2002; Millward, 2004; Tipton and Wolfe, 2004): starvation induces body protein loss. For a variety of reasons analyzed earlier by the Committee on Military Nutrition Research (CMNR) (IOM, 1995), soldiers in a stressful, high-energy-expenditure environment typically fail to increase their energy intake enough to match their energy expenditure. This situation fits the definition of starvation, and in keeping with its cardinal features, these soldiers lose fat and lean tissue mass. Their physiologic state appears to be the same as that of starvation that is induced simply by low food consumption. Thus, despite ample carbo-

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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hydrate intake, circulating concentrations of insulin-like growth factor-1 and 3,5,3′-triiodothyronine are decreased as occurs in conventional starvation, and they increase when the energy gap is narrowed, even if there is no other change in the stressful environment (Friedl et al., 2000).

Carbon oxidation always equals energy expenditure, and when energy expenditure exceeds food energy consumption, the body draws on endogenous fat, its chief energy store. Fat loss is therefore an essential feature of starvation. But the situation with regard to protein loss is unclear. Why does it occur? How avoidable is it? Factors that affect its magnitude are enumerated below.

Micronutrient Status

Mineral deficiencies, particularly those of potassium (Rudman et al., 1975), phosphorus (Rudman et al., 1975), zinc (Khanum et al., 1988; Wolman et al., 1979), and, presumably, magnesium, impair the normal protein-sparing adaptation to starvation.

Absence of a Catabolic State

Tissue injury, inflammation, and systemic infection reverse the physiologic adaptation to starvation and increase body nitrogen loss (Hoffer, 1999b).

Magnitude of the Energy Deficit

This phenomenon is illustrated by a study in which male volunteers with a body mass index (BMI) of 24.5 kg/m2 participated in an 8-week US Army Ranger course (Friedl, 1997; Friedl et al., 2000). The program consisted of four periods of an initial several days of ad libitum feeding followed by seven to ten days of food restriction in a setting of daily energy expenditures of 4,000 to 4,500 kcal, thermal stress, and sleep deprivation. In the first of two studies, food intake was restricted to 1,400 kcal, with 52 g of protein per day (similar to the Minnesota study). In the second study, supplemental food provided an additional 400 kcal and 15 g of protein. In both experiences food intake during the brief recovery periods did not fully compensate for the deficits incurred during the restriction periods. The greater intake of energy (but also of protein; see below) by the second group produced marked benefits. In particular, the better-fed group experienced less weight loss and their percentage of fat-free mass (FFM) was significantly greater at the end of the study (Friedl et al., 2000).

Fat Store

Some experts claim that very obese, starving people lose body nitrogen more slowly (and have a slower rate of nitroten loss as a fraction of total weight

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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loss) than starving people of normal weight (Elia et al., 1999; Van Itallie and Yang, 1977). Since severely obese people invariably lose FFM during therapeutic starvation, it would seem that starving, nonobese soldiers must inevitably experience FFM loss. It should be borne in mind, however, that severe obesity increases the lean tissue compartment (Drenick, 1975; Henry et al., 1986), and at least some of the lean tissue loss during therapeutic starvation occurs simply because a smaller body requires less muscle to be lifted and moved. From this perspective, normal-weight or only mildly obese people may actually conserve body protein more effectively than severely obese ones during starvation.

It is certainly true that very obese people tolerate starvation with a greater sense of well-being and survive it for longer time. Adults of normal weight die after fasting for approximately 2 months, whereas severely obese people have survived fasts lasting many months (Barnard et al., 1969; Thomson et al., 1966). The longest monitored fast on record was by a 27-year-old man who initially weighed 207 kg and survived 382 days of uninterrupted fasting (Stewart and Fleming, 1973). Friedl and colleages (1994) cite a description of the starvation that occurred among the British forces during the Turkish siege of Kut from December 1915 to April 1916. Soldiers who began with superabundant fat stores survived, whereas those who began with a smaller fat reserve soon died in the cold winter climate (Hehir, 1922).

A study by Friedl and colleagues (1994) provides important insight into this phenomenon. The body composition of 55 men was determined before and after their successful completion of an 8-week US Army Ranger course in which energy intake was unusually low (1,300 kcal per day during the restriction periods). Body fat was an average of 14.3 percent at the start and decreased to an average of 5.8 percent at the end of the course. The remarkable finding was that, during progressive starvation, body fat stabilized at a minimum of 5 percent. The men who reached this limit continued to lose weight, but the source of the weight loss was now FFM. This observation suggests that 5 percent body fat represents a biological limit that is essential for successful adaptation to starvation. US Army data reviewed by Friedl (1995) suggest the contribution of lean tissue loss to total weight loss increases gradually as body fat falls below 10 percent. Nevertheless, the 5 percent limit appears to represent a “metabolic floor” that also approximately coincides with the psychological limit of voluntary participation (Friedl, 1995). As long as body fat remains above this critical level, a high-protein intake can spare body protein, but once it falls below it, protein-sparing is no longer possible. Obese people therefore survive prolonged starvation longer than lean ones because it takes longer to deplete their fat store to the critical level below which protein catabolism accelerates and disability becomes marked.

Comparison has been made between the Minnesota study and modern calorie-restriction studies like the Biosphere 2 study which involved normal-weight individuals (Heilbronn and Ravussin, 2003). This comparison is complicated by the fact that the average BMI of the Minnesota volunteers was only 21.4 when

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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they embarked on their starvation regimen. Thus, even before they began to starve, the Minnesota volunteers had BMIs comparable to modern adults who would be considered calorie restricted. The BMIs of most fit young men of the 21st century typically range from 23 to 25. The crucial determinant of well-being and physical function is more likely to be the absolute lean tissue mass that exists for a given body structure than a percentage reduction. At the end of the starvation phase of the Minnesota study, the average BMI had fallen to 16.3; this was associated with a severity of fat and lean tissue depletion that was incompatible with normal physiologic function. Had the baseline BMI of the Minnesota volunteers been greater, their final BMI would presumably have been closer to the range reported in modern calorie-restriction experiences. Taken together, these considerations suggest that elite soldiers being considered for extended hypocaloric field maneuvers should have normal fat and muscle stores as indicated by a normal physical examination, a BMI not less than approximately 23, and body fat not less than an appropriate minimum, such as 15 percent.

Protein Intake

While it is true that energy deficiency worsens nitrogen balance, it is also true that an increase in protein intake improves nitrogen balance over a wide range of energy intakes from deficient to maintenance (Munro, 1964; Shaw et al., 1983). It was not at first appreciated that a high protein intake protects the lean tissue store during starvation because the early studies were of short duration. Short-duration studies are confounded by a transient loss of body nitrogen, called “labile protein,” that occurs immediately after energy (or protein) intake is reduced, and by the failure to allow sufficient time for physiologic adaptation to the new diet. When nitrogen balance studies are carried out long enough for the transient effect of labile protein loss to end and metabolic adaptation to take effect—a process that requires several days (Hoffer, 1999a, b)—high protein intakes are protein sparing in many energy-deficient states (Hoffer, 2003).

The protein-sparing effect of increased dietary protein is not necessarily limited to obese persons. In one study, nonobese men were calorie restricted for 10 weeks while consuming 93 g of protein per day. The men lost 7.4 kg (BMI fell from 24.9 to 22.6), 83 percent of which was fat (Velthuis-te Wierik et al., 1995). This is the composition of adipose tissue, which is approximately 85 percent fat and 15 percent FFM (Garrow, 1982; Grande and Keys 1980; Waki et al., 1991). In the Biosphere 2 experiment, eight normal men and women starved for 6 months, then remained in energy equilibrium for 18 months during which they consumed 2,200 kcal per day including 82 g of protein (Walford et al., 2002; Weyer et al., 2000). The men’s BMI decreased from 23.7 to 19.3 and the women’s from 21.2 to 18.5 (Walford et al., 2002). In the five persons in whom it was measured, body fat fell to 10 percent (significantly less than the 20 percent body fat in a matched normal comparison group), but their FFM was normal

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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(Weyer et al., 2000). Several studies in the obesity field have demonstrated zero nitrogen balance in normally active, moderately obese people adhering to very low energy diets supplying 1.5 g of protein per kg of ideal body weight per day (Gelfand and Hendler, 1989; Piatti et al., 1994). The proposition that lean tissues need not be lost during starvation is further supported by data from military trainees who lost body fat (i.e., starved) during basic training without food restriction. In one study, moderately obese female army trainees lost 2.2 kg of fat but simultaneously gained 1.7 kg of FFM (Friedl, 1995). In a study of obese male army recruits, basic training was associated with an average of loss of 12.5 kg within the first 3 months, virtually all of it as fat (Lee et al., 1994). Protein intakes in all these studies were substantially greater than in the Minnesota study and in published US Army Ranger field studies. One may conclude that important protein sparing may well be achievable in starving, normal-weight soldiers by increasing the protein content of their rations.

Another issue to be considered is whether the high level of physical activity required during maneuvers increases the protein requirement. Sports experts advise athletes to consume approximately 1.5 g of protein per kg of body weight every day. This is nearly twice the RDA (IOM, 2002) and nearly three times the average minimum requirement (Fielding and Parkington, 2002; Tipton and Wolfe, 2004). Could the increased protein requirement incurred by exercise add to the high-protein requirement induced by starvation? This issue was addressed by the CMNR (IOM, 1999), who found there was insufficient evidence to conclude that high-level physical activity increases the normal protein requirement. More recent reviews have come to the same conclusion (Fielding and Parkington, 2002; Tipton and Wolfe, 2004). Since the increased food intake necessary to meet a high-energy requirement automatically increases protein intake, the most cogent reason for advising athletes to consume a lot of protein is that this is what they naturally do.

In summary, lean tissues can be conserved during starvation by four mechanisms: (1) the only modest adipose tissue unloading—and hence less absolute weight loss and less disuse muscle atrophy—that occurs when baseline fat stores are normal or only moderately increased; (2) a high, or at least maintained, level of physical activity (Ballor and Poehlman 1994; Prentice et al., 1991); (3) the prevention of a severe depletion of the fat reserve; and (4) substantially greater protein intake than in the Minnesota experiment. Despite the common assumption that protein wasting is unavoidable in the presence of energy deficiency (IOM, 1995), there are good reasons to predict that the lean tissue stores of soldiers in the field can in fact be largely, if not completely, protected by increasing their protein intake. The daily ration currently under consideration provides 2,400 kcal. If, like other US Army rations (Cline and Warber, 1999), 15 percent of the energy is from protein, this ration will provide 90 g of protein per day, or 1.15 g of protein per kilogram of body weight for the average 78 kg US male soldier (IOM, 1999). This may be sufficient to prevent starvation-induced

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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lean tissue loss. Indeed, US Army Ranger course participants who consumed considerably less than 90 g/day suffered only modest losses of FFM and their physical performance appeared to be maintained (Friedl, 1995, 1997). In the Ranger study described earlier, in which daily energy and protein intakes during restriction periods were 1,800 kcal and 67 g of protein, respectively, FFM decreased by 6 percent or 4 kg (Friedl et al., 2000). Upper arm muscle cross-sectional area decreased from 68 to 60 cm2, but 60 cm2 remains at the upper 85th percentile for normal age-matched men. Will 90 g of protein per day prevent even these losses? Would 120 g of protein per day (1.5 g of protein per kg) be even more effective? This larger amount of protein would be provided by a 2,400 kcal ration with 20 percent of energy from protein and would conform to the current expert recommendation of 1.5 g/kg for athletes (Fielding and Parkington, 2002; Tipton and Wolfe, 2004). Although 120 g of protein per day seems to exceed the military protein RDA (MRDA) of 100 g per day, first established in 1947, it actually does not. In 1947 the average male soldier weighed only 68 kg (IOM, 1999); the original MRDA was therefore equivalent to a protein intake of 1.5 g/kg of body weight.

Potential drawbacks to a high-protein diet include unpalatability, early satiety, and increased obligatory urine volume to eliminate the additional urea osmoles (Friedl, 1999). However, an increase of protein intake from 90 to 120 g per day would not increase obligatory urine volume because urea is an “ineffective osmole” (Kamel et al., 2004). With regard to satiety and palatability, it is worth recalling that protein comprised 30 to 35 percent of the daily energy intake of paleolithic humans. This is equivalent to 2.5 to 3.5 g/kg (Eaton and Cordain, 1997; Eaton et al., 1996). It seems very likely that a palatable diet providing a “mere” 1.5 g/kg of protein could be devised.

CONCLUSIONS

If soldiers are required to starve for only three to seven days before refeeding, it does not matter how much protein they consume, and the design of the ration should focus on features such as palatability. Field studies do show, however, that ad libitum feeding over the few days following seven to ten days of food restriction is insufficient to make up the energy deficit incurred, so soldiers returning too quickly to the field will experience progressive starvation (Friedl et al., 1994). It is also possible that a highly successful ration could be put to use for longer periods than initially planned for. The following conclusions and suggestions are offered with these possibilities in mind.

Contrary to what is commonly assumed, it is very likely that the lean tissue store of normal-weight persons can be largely conserved during starvation through a combination of a high-protein intake, physical activity, and avoidance of severe body fat loss. This hypothesis has not been tested in a field situation. The prediction is that a hypocaloric ration providing 2,400 kcal and 90 g of

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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protein per day will spare the lean tissue store of soldiers on extended stressful maneuvers. It would be interesting and useful to determine whether a ration providing 2,400 kcal and 120 g of protein is even more effective, as well as practical and palatable. The protein-sparing effect of high-protein intakes will not be demonstrable unless balance studies are long enough to allow for metabolic adaptation.

The energy deficit should be minimized. Protein sparing is only possible when body fat is above a minimum of approximately 5 percent of body weight. Energy-deficient states are psychologically very unpleasant and appear to be increasingly so as the lower fat limit is approached (Friedl, 1997). The psychological unpleasantness of hypocaloric rations may well be their most debilitating short-term feature (Keys et al., 1950). As has already been pointed out (Friedl, 1995; Friedl et al., 1994), it is important, when selecting elite soldiers for stressful missions, to consider their starting body composition. Under starvation conditions, very lean and muscular does not translate into better.

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Vitamins C and E in the Prevention of Oxidative Stress, Inflammation, and Fatigue from Exhaustive Exercise

Maret G. Traber, Oregon State University

Angela Mastaloudis, Pharmanex

INTRODUCTION

This paper attempts to address the effects of exercise on oxidative stress and immune function and whether increasing the intake of antioxidants would reduce this stress, first in energy balance conditions and then in energy deficit conditions. Findings from our studies in ultramarathon runners may help answer this and the specific following questions:

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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  1. What are the types and levels of direct antioxidants (e.g., vitamins C and E, carotenoids) that could be added to rations for short-term use by soldiers during high-tempo, stressful, repetitive combat missions to enhance performance and/or improve recovery during combat missions?

  2. Would certain nonvitamin antioxidants help performance?

  3. What is the impact of exercise on oxidative stress and immune function? Will increasing the intake of antioxidants reduce this stress in energy balance conditions and then in energy deficit conditions?

  4. Is there any concern with megadoses of antioxidants—should soldiers be already taking supplements? For example, could megadoses of antioxidants negatively affect performance or adaptation?

OXIDATIVE STRESS GENERATED DURING EXERCISE

The human body continuously produces reactive oxygen species (ROS) as a result of normal metabolism in the mitochondria (Halliwell and Gutteridge, 1999). ROS are an unavoidable but necessary byproduct of cellular respiration. ROS also have a beneficial role in that leukocytes use radicals to help kill bacteria. This action produces a large increase in oxygen use, called a “respiratory burst,” to catalyze hydrogen peroxide with chloride ions to create a strongly antiseptic hypochlorite ion. Unfortunately, hypochlorite is also a strong oxidizing agent and can produce free radicals.

In response to endurance exercise, the body’s oxygen consumption can increase 10 to 20 times (Åstrand and Rodahl, 1986), while skeletal muscle oxygen consumption can increase 100 to 200 times (Halliwell and Gutteridge, 1999). This increased oxygen consumption may produce ROS in amounts that exceed the body’s antioxidant supplies. Clearly, exercise can cause oxidative stress resulting in lipid peroxidation (Alessio, 2000; Child et al., 1998; Duthie et al., 1990; Hessel et al., 2000; Marzatico et al., 1997; Mastaloudis et al., 2001; Rokitzki et al., 1994), DNA damage (Hartmann and Niess, 2000), and, possibly, protein oxidation (Alessio, 2000; Tirosh and Reznick, 2000).

Electrons “leaking” from the mitochondria during exercise are considered a main source of oxidative stress (Halliwell and Gutteridge, 1999). Other potential sources of ROS during exercise include enhanced purine oxidation, damage to iron-containing proteins, disruption of Ca2+ homeostasis (Jackson, 2000), and NADPH oxidase (Hessel et al., 2000). These exercise-induced ROS are also thought to modulate acute phase inflammatory responses (Cannon and Blumberg, 2000).

We found that during an ultramarathon race (32-mile forest trail through hilly terrain), as compared with a sedentary trial, deuterium-labeled vitamin E disappeared from the plasma faster (disappearance rates of 2.8 × 10–4 versus 2.3 × 10–4, p < 0.03) and lipid peroxidation increased (75 ± 7 pg/ml at prerace to 131 ± 17 at postrace (p < 0.02) (Mastaloudis et al., 2001). Lipid peroxidation

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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was assessed by measuring plasma F2-isoprostanes (F2-IsoPs), prostaglandin-like compounds produced by free-radical catalyzed lipid peroxidation of arachidonic acid (20:4 n-6, a long-chain polyunsaturated fatty acid) (Morrow et al., 1990). F2-IsoPs are widely accepted as sensitive and reliable measures of in vivo lipid peroxidation (Roberts, 1997). Importantly, F2-IsoPs have proatherogenic biological activity, including vasoconstriction and activation of platelet aggregation (Nieman et al., 2002; Roberts and Morrow, 2000). Moreover, they have been shown to recruit proatherogenic monocytes and induce monocyte adhesion (Leitinger et al., 2001). Thus, endurance exercise not only increases oxidative stress, but also increases a proatherogenic response.

MODULATION OF OXIDATIVE STRESS DURING AN ULTRAMARATHON BY VITAMINS C AND E

Based on our findings that an ultramarathon race increases oxidative stress (Mastaloudis et al., 2001), we hypothesized that prior supplementation with antioxidants (vitamins C and E) would decrease oxidative stress during distance running (Mastaloudis, 2004; Mastaloudis et al., 2004a, b). If the antioxidant supplements decreased oxidative stress, they should decrease lipid peroxidation and inflammation, slow α-tocopherol use, decrease DNA damage, decrease muscle damage, and improve recovery. To test these hypotheses, we carried out a randomized, double-blind study in ultramarathon runners (n = 11 women, 11 men) who consumed either (1) antioxidants (AO) [1,000 mg vitamin C (500 mg twice daily) and 300 mg vitamin E (400 IU RRR-α-tocopheryl acetate)] or (2) matching placebos (PL) for seven weeks (six weeks before through one week after the race). The race was a 50 km (32 mile) ultramarathon that took place in the hills of Corvallis, Oregon. The study design is shown in Figure B-18.

Subject Characteristics and Plasma Antioxidant Concentrations

Subjects were approximately 40 years of age and were recreationally trained endurance runners. Complete descriptions of the subjects have been published (Mastaloudis, 2004; Mastaloudis et al., 2004b). Plasma α-tocopherol and ascorbic acid concentrations were similar in the two groups before supplementation (Mastaloudis, 2004). Following six weeks of supplementation, the PL-group plasma concentrations were unchanged. In contrast, the AO-group α-tocopherol plasma concentrations increased from 28 ± 2 to 45 ± 3 µM (p < 0.0001) and were higher than in the PL group (p < 0.0007). Similarly, the AO group had a higher ascorbic acid plasma concentration, 121 ± 9 µM, than did the PL group, 78 ± 9 µM (p < 0.0007) following supplementation. Note that in both the PL and AO groups the ascorbic acid concentrations are well into the range for repleted subjects (Levine et al., 1996, 2001).

All subjects completed the race. Run times and intensity were similar among

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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FIGURE B-18 Study Design. Subjects (n = 22) were randomly assigned in a double-blind fashion to one of two groups: (1) PL [(1,000 mg of citric acid (500 mg twice daily) and 300 mg of soybean oil] or (2) AO [1,000 mg ascorbic acid (500 mg twice daily) and 300 mg RRR-α-tocopheryl acetate]. Blood samples were obtained before supplementation (baseline); after three weeks of supplementation (compliance); 24, 12, and 1 hours before the race. Samples were also taken at mid-race at kilometer 27 (~ 5 h), immediately postrace, 2 h postrace (approximately 10 h), and daily for six days postrace (1–6 days, 24–144 h). All samples were fasting morning blood draws except 12 h, mid-, post-, and two h post-race.

NOTE: AO = antioxidant; PL = placebo.

SOURCE: Summarized from Mastaloudis (2004); Mastaloudis et al. (2004a), used with permission from Elsevier.

treatment groups and genders: 7.1 ± 0.2 h at a pace of 13.7 ± 0.4 minutes per mile and a heart rate of 146 ± 2 beats per minute. Energy expenditure was calculated based on the average heart rate during the run and the corresponding oxygen consumption (VO2), multiplied by the time it took each subject to finish the race (Mastaloudis et al., 2004b). Energy expenditure was approximately 7,000 kcal for men and 5,000 kcal for women; both consumed about 2,000 kcal on race day and were in caloric deficit (Table B-6).

TABLE B-6 Race Results

 

Women

Men

AO (n = 6)

PL (n = 5)

AO (n = 6)

PL (n = 5)

Run Time (hr)

7.1 ± 0.4

7.3 ± 0.6

6.8 ± 0.4

6.8 ± 0.2

Energy Expenditure (kcal)

4,997 ± 207

4,958 ± 187

6,928 ± 558

7,006 ± 297

Energy Intakea (kcal)

1,844 ± 137

2,040 ± 221

2,530 ± 325

2,468 ± 279

Vitamin E Intake (mg)

3 ± 1

2 ± 1

3 ± 1

4 ± 1

Vitamin C Intake (mg)

39 ± 14

32 ± 9

28 ± 5

17 ± 5

NOTE: AO = antioxidant; PL = placebo.

aWomen versus men p < 0.05.

SOURCE: Mastaloudis et al. (2004b), used with permission from Elsevier.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Vitamins C and E intakes from foods consumed during race day were compiled. During the run vitamin C intake was < 50 mg for most subjects, and vitamin E intake was < 5 mg.

Vitamin C, Vitamin E, and Lipid Peroxidation

Plasma F2-isoprostanes (F2-IsoP) concentrations increased in the PL group in response to the race, but prior supplementation with vitamins C and E completely suppressed the increase in the AO group (Figure B-19) (Mastaloudis et al., 2004a). At postrace, when oxidative stress was maximal, F2-IsoP concentrations were inversely correlated with both the ratio for α-tocopherol:lipids (R = −0.61, p < 0.003) and with ascorbic acid (R = −0.41, p = 0.05) (Mastaloudis et al., 2004a), providing further documentation that antioxidants were responsible for preventing lipid peroxidation.

Both men and women in the PL group responded to the run with similar F2-IsoP concentration increases (Mastaloudis et al., 2004a). However, men’s and

FIGURE B-19 Antioxidant supplementation prevents the increase in lipid peroxidation as observed in ultramarathon runners. Plasma F2-isoprostanes concentrations increased from pre- to postrace only in the placebo (PL) group (28 ± 2 to 41 ± 3 pg/ml; p < 0.01). Additionally, postrace F2-isoprostanes concentrations were significantly higher in the PL group than in the antioxidant group (p < 0.001).

SOURCE: Mastaloudis et al. (2004a), used with permission from Elsevier.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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women’s responses were markedly different during recovery. In PL women, F2-IsoP concentrations returned to baseline within two hours postrace, while in PL men, higher F2-IsoP concentrations persisted for the duration of the study (six days) (Mastaloudis et al., 2004a). This difference in oxidative stress in men and women has been observed previously. Healthy young men compared with age-matched women had greater concentrations of markers of oxidative stress (plasma TBARS [thiobarbituric acid reactive substances] and urinary 8-Iso-PGF2). Following antioxidant supplementation (600 mg vitamin C and 300 mg vitamin E daily for 4 weeks), levels of lipid peroxidation markers were normalized to concentrations similar to those observed in the women (Ide et al., 2002). Thus, men in comparison with women are subjected to continued higher oxidative stress in the absence of antioxidant supplementation.

Cytokine Levels after the Race

Very few studies have examined the effects of antioxidants on both exercise-induced oxidative stress and inflammation (Childs et al., 2001; Nieman et al., 2002). We found that AO supplementation had no effect on exercise-induced increases in tumor necrosis factor (TNF)-a, interleukin (IL)-6, C-reactive protein (CRP), or IL-1, despite the finding that increases in lipid peroxidation were prevented (Mastaloudis et al., 2004a). Similarly, ascorbic acid (1,500 mg/day) consumption for one week before an ultramarathon did not prevent exercise-induced increases in plasma F2-IsoPs, lipid hydroperoxides, or IL-6 (proinflammatory cytokine) (Nieman et al., 2002). Postexercise supplementation with vitamin C (approximately 1,000 mg/day) and n-acetyl-cysteine for one week also had no effect on exercise-induced IL-6 increases (Childs et al., 2001). Army recruits that participated in an intensive 48-hour final military endurance exercise were also shown to have increased CRP, but the effect of antioxidants were not tested (Brull et al., 2004). In general, antioxidants do not modulate increases in cytokine concentrations in response to exercise.

Assessing DNA Damage

The ultramarathon was a sufficiently strenuous exercise that, by mid-race, the runners exhibited DNA damage as assessed with the comet assay (a whole-cell electrophoresis assay that estimates DNA damage) (Mastaloudis et al., 2004b). However, the proportion of cells with DNA damage returned to baseline by the end of the race, declined below baseline values two days after the race, and remained low for six days after the race (Mastaloudis et al., 2004b). Both men and women within each treatment group had similar circulating AO levels, but the women had a higher proportion of DNA damage after the race. In addition, the women in the AO group were more protected, showing a decrease in the

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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proportion of DNA damage on the day following the ultramarathon race, while men experienced little benefit.

Overall, this exercise appeared to induce a temporary increase in DNA damage. This increase, however, has no apparent adverse effects and may be beneficial because it appears to induce the replacement of damaged cells.

Muscle Damage Following Running

Runners experienced muscle damage after the ultramarathon: deficits in maximal force production by the knee extensors and flexors were documented (Mastaloudis et al., in press). Prior supplementation with vitamins C and E did not prevent muscle damage or fatigue or improve recovery. The ultramarathon run may have been so damaging that it overwhelmed the protective effects of the antioxidants. For example, vitamin C was found to be protective in a more moderate exercise protocol (60 minutes of box-stepping exercise), in which supplementation enhanced the rate of recovery from maximal force deficit (Jakeman and Maxwell, 1993).

Plasma markers of muscle damage were increased by the endurance exercise in our study (Mastaloudis et al., in press) and were unaffected by AO supplementation. Both lactate dehydrogenase (LDH) and creatine kinase (CK) increased in response to the race; LDH peaked at postrace and CK reached maximal values 2 h and 1 day postrace; neither was affected by AO treatment. These observations are in agreement with others. There was no influence on increased CK concentrations in response to a 90 minute treadmill run by two weeks prior supplementation with 500 mg vitamin C and 400 mg vitamin E (Petersen et al., 2001). Our findings are in contrast, however, with other studies (Rokitzki et al., 1994) that reported prior supplementation with 200 mg vitamin C and 400 IU vitamin E for 4.5 weeks diminished increases in CK following a 90 km ultramarathon.

Our study also showed that vitamins C and E did not prevent LDH increases after distance running. However, daily supplementation with 1,200 IU α-tocopherol for four weeks prior to running diminished LDH increases following six successive days of running (Itoh et al., 2000), suggesting that a larger dose of vitamin E is required to reduce muscle damage resulting from endurance exercise. The results seem influenced not only by the level of exercise but also by the amount, duration, and type of supplemental AO.

Endogenous Mechanisms to Increase Antioxidant Defenses

Plasma ascorbic acid concentrations increased in both the AO and PL groups during the 50 km ultramarathon run, with significant increases at mid-race, and at postrace compared with levels measured prerace; levels returned to prerace values two hours after the race (Mastaloudis et al., 2004a, b). Increases in plasma

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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ascorbic acid in response to vigorous exercise have been reported in some (Duthie et al., 1990; Kaikkonen et al., 1998; Mastaloudis et al., 2001; Petersen et al., 2001; Rokitzki et al., 1994; Viguie et al., 1993), but not all (Meydani et al., 1993; Peters et al., 2001a, b) studies. Exercise-related increases in circulating cortisol has been suggested to promote efflux of ascorbic acid from the adrenal gland and the mobilization of ascorbic acid from other tissue sites such as leukocytes or erythrocytes (Gleeson et al., 1987). Similarly, some (Nieman et al., 2000; Peters et al., 2001a, b), but not all (Nieman et al., 2002), studies demonstrated that exercise-related increases in circulating cortisol diminish with vitamin C supplementation. Taken together, these findings suggest that oxidative stress may regulate cortisol secretion.

Plasma uric acid concentrations also increased in response to the run, consistent with the findings of others (Hellsten et al., 1997; Liu et al., 1999; Rokitzki et al., 1994), and the increase may be explained by enhanced purine oxidation resulting from exercise (Hellsten et al., 1997; Liu et al., 1999; Rokitzki et al., 1994).

Concurrent increases in plasma ascorbic and uric acids may reflect the body’s response to extreme exercise by enhancing AO defenses, including increased AO enzymes (Marzatico et al., 1997) and AO nutrients (Child et al., 1998; Rokitzki et al., 1994; Viguie et al., 1993).

Some studies investigating the effects of vitamin E supplementation on endurance runners have reported increases in plasma α-tocopherol concentrations in both the AO and the PL groups following exercise (Buchman et al., 1999; Rokitzki et al., 1994; Vasankari et al., 1997). We (Mastaloudis et al., 2004a) observed increased plasma α-tocopherol concentrations during exercise in the AO group only. Plasma tocopherols are transported entirely within lipoproteins and fluctuate with lipoprotein concentrations (Traber and Jialal, 2000) and after correcting α-tocopherol for lipids, no significant changes in α-tocopherol/lipid concentrations were observed in either group (Mastaloudis et al., 2004a). In the only other study to report both α-tocopherol and α-tocopherol/lipid concentrations (Buchman et al., 1999), fluctuations in lipoproteins explained the differential responses in the AO and PL groups. Thus, the increase in plasma α-tocopherol concentrations during the exercise may be a result of fluctuations in lipoprotein concentrations rather than an actual increase due to exercise.

Increases and Depletions of Plasma Lipids

Plasma lipids (total cholesterol plus triglycerides) increased during the race, but decreased to below prerace levels two hours after the race and remained low for three days (Figure B-20). These data suggest that extreme endurance exercise depletes lipid stores that subsequently remain depleted for several days. Rations should provide adequate fat content and total kcals to ensure that tissue stores of lipids are maintained for endurance and multi-day physical work in the field.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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FIGURE B-20 Plasma lipids increase during the race but are depleted for three days postrace. No differences in plasma total lipids (total cholesterol plus triglycerides) were observed between genders or among treatment groups within each gender.

NOTE: *Compared with prerace levels, plasma total lipids were higher at mid-race (p < 0.004), but were lower two hours (p < 0.01), one day (p < 0.0001), two days (p < 0.0001), and three days (p < 0.01) postrace.

SOURCE: Adapted from Mastaloudis (2004), used with permission.

Conclusions

ROS generated in response to exercise cause oxidative damage (Mastaloudis et al., 2001, 2004a), stimulate an inflammatory response (Vassilakopoulos et al., 2003), and damage skeletal muscle (Cannon and Blumberg, 2000; Sjodin et al., 1990). Hypothetically, AO supplementation could prevent exercise-induced oxidative damage, inflammation, and muscle damage. We found, however, that while supplementation with vitamins C and E prevented increases in lipid peroxidation in response to endurance exercise (Mastaloudis et al., 2004a), they had no apparent effect on DNA damage (Mastaloudis et al., 2004b), inflammation (Mastaloudis et al., 2004a), or muscle damage (Mastaloudis et al., in press). These results suggest that the mechanism of oxidative damage is operating independently of the inflammatory and muscle damage responses (Nieman et al., 2002).

Preventing production and enhancing clearance of F2-IsoPs may be more beneficial than preventing inflammation. F2-IsoPs have demonstrated proatherogenic biological activity, including vasoconstriction and activation of platelet aggregation (Nieman et al., 2002; Roberts and Morrow, 2000). In addition, they are known to recruit proatherogenic monocytes and induce monocyte

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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adhesion (Leitinger et al., 2001). In contrast, the muscle damage-induced inflammatory response stimulates recovery from exercise by inducing regeneration of damaged tissue and recruitment of satellite cell proliferation (Malm, 2001). In our studies, AO supplementation proved to prevent the damaging increase in lipid peroxidation without influencing inflammation. This is especially important because preventing exercise-induced inflammation could inhibit muscular adaptation to physical activity, the so-called “training effect” of exercise.

Supplementation of both vitamins C and E appears beneficial in exercise. Certainly, the ultramarathon runners were adequately nourished with respect to vitamin C, but studies in cigarette smokers suggest that vitamin C is necessary to maintain vitamin E concentrations (Bruno et al., 2005). Prior supplementation with vitamin E alone may be possible, but the assault ration should contain vitamin C not only for its own benefits but also for maintaining vitamin E concentrations.

In healthy adults, there are no obvious adverse effects of either vitamin C or E supplements alone or in combination (Hathcock et al., 2005), and the Tolerable Upper Intake Levels are 2,000 and 1,000 mg, respectively (IOM, 2000). A recent meta-analysis assessed the combined results of 19 clinical trials of vitamin E supplementation for various diseases reported that patients who took supplements of 400 IU/day or more were 6 percent more likely to die from any cause than those who did not take vitamin E supplements (Miller et al., 2005). However, three other meta-analyses that combined the results of randomized controlled trials designed to evaluate the efficacy of vitamin E supplementation in cardiovascular disease found no evidence that vitamin E supplementation up to 800 IU/day significantly increased or decreased cardiovascular disease mortality or all-cause mortality (Eidelman et al., 2004; Shekelle et al., 2004; Vivekananthan et al., 2003). At present, there is no convincing evidence that vitamin E itself increases the risk of death from cardiovascular disease or other causes. Therefore, AO vitamin supplements could be added to assault rations to prevent the adverse increase in lipid peroxidation as described in the ultramarathon runners in our study (Mastaloudis et al., 2004a).

ACKNOWLEDGMENTS

We thank the runners and the support from National Institute of Environmental Health Sciences Grant ES11536 and National Institutes of Health Grant DK59576. The following individuals provided supplements and ergogenic aids: Jim Clark, Cognis Health and Nutrition; Klaus Krämer, BASF; Tim Corliss, Clif Bar; Jeff Zachwieja, Gatorade.

The following individuals played key roles in our study: Dawn W. Hopkins, The Department of Exercise and Sport Science, Linus Pauling Institute, Oregon State University, Corvallis; Scott Leonard, Linus Pauling Institute, Oregon State University, Corvallis; David Yu, Linus Pauling Institute, Oregon State Univer-

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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sity, Corvallis; Robert P. O’Donnell, Statistics, Oregon State University, Corvallis; Roderick H. Dashwood, Linus Pauling Institute, Oregon State University, Corvallis; Balz Frei, Linus Pauling Institute, Oregon State University, Corvallis; Jason D. Morrow, Departments of Medicine and Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee; and Sridevi Devaraj, Department of Pathology, the University of California Medical Center, Sacramento; Jeffrey J. Widrick, The Department of Exercise and Sport Science, Oregon State University, Corvallis.

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Zinc, Magnesium, Copper, Iron, Selenium, and Calcium in Assault Rations: Roles in Promotion of Physical and Mental Performance

Henry C. Lukaski and James G. Penland, USDA-ARS Grand Forks Human Nutrition Research Center

INTRODUCTION

Military personnel are exposed to environmental, physical, and mental stressors during combat and require adequate dietary intakes of energy, water, and micronutrients for optimal performance. During deployment, soldiers decrease food consumption up to 50 percent, resulting in a suboptimal intake of energy and micronutrients (Baker-Fulco, 1995). Thus, reduced food intake and increased losses of minerals during assault operations suggest the need to evaluate mineral nutrition of military personnel (Shippee, 1993).

Only male soldiers participate in first-strike assault operations. These missions occur for repetitive brief periods (three to seven days), followed by short recovery periods (one to three days) that can last for months. Under these circumstances, it is unlikely that such brief durations of reduced micronutrient intake will elicit severe mineral deficiencies. However, repeated bouts of first-strike assaults without adequate replenishment of minerals may predispose soldiers to a reduced mineral nutritional status and result in impaired physiological and psychological function and performance.

This review addresses the mineral needs of male soldiers. It does so by comparing the prevalence of inadequate mineral intakes of civilian and military men and summarizing the effects of restricted and supplemental mineral intakes on their performance. Additionally, it provides a strategy for increasing food and nutrient intake to promote optimal performance of the male combat soldier. Findings from studies of women with documented mineral depletion are described to highlight impairments in performance that would be applicable to men with similarly reduced mineral nutritional status.

The following are specific questions that this review attempts to answer:

  • Which of the minerals might reach deficit levels, given the high-stress, high-intensity scenario? Given existing information that suggests that soldiers probably consume insufficient amounts of zinc during military

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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operations, and that they could become zinc deficient, are there potential effects on health or performance?

  • What are the types and levels of cofactors in antioxidant and other biochemical reactions with high metabolic flux (e.g., zinc, manganese, copper, selenium, or others) that could be added to assault rations to enhance performance during combat missions? Does the presence of preexisting malnutrition make a difference?

  • Is there any concern with taking megadoses of minerals; should soldiers be already taking supplements?

LIMITING MINERALS IN THE DIET

Estimating a group’s adequate intake of a nutrient is achieved through comparison with the Estimated Average Requirement (EAR). If an EAR is not available, then the Adequate Intake (AI) is used. The Recommended Dietary Allowance (RDA) is not used to assess the adequacy of nutrient intakes by groups (IOM, 2000a).

Inadequate Dietary Mineral Intakes in Adults

Epidemiological surveys using dietary recall reveal (NHANES III, Continuing Survey of Food Intake of Individuals, and US Food and Drug Administration Total Diet Study) that intakes of some minerals by the US population do not meet the Dietary Recommended Intake (DRI) recommendations. Among men ages 19 to 50 years, 50 percent did not meet the AI for calcium or the EAR for magnesium (Table B-7). Inadequate zinc intakes were found among 10 percent of men, but iron intakes generally met the EAR (6 mg) (IOM, 1997, 2000b, 2001).

Nutritional surveys reveal wide-ranging estimates of possible copper deficiency in the US population (IOM, 2001). Although findings of the NHANES III and Continuing Survey of Food Intake of Individuals showed no men with copper intakes less than the EAR, the US Food and Drug Administration Total Diet Study revealed that 25 percent of men consume less than the EAR for copper. Analyses of diets from ten multinational studies indicated that copper intakes were less than the EAR in 11 percent of the population (Klevay et al., 1993). Another study analyzed duplicate diets of randomly selected adults in Baltimore, Maryland, and found that 36 percent of the adults had dietary copper intakes less than the EAR (Pang et al., 2001).

Inadequate Dietary Mineral Intakes in Military Personnel

Based on observation of the foods soldiers consume (Rose et al., 1987), soldiers frequently have inadequate intakes of certain minerals. Zinc and magne-

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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TABLE B-7 Dietary Reference Intakes of Minerals in Diets of American Men Ages 19–50 Years and Actual Intakes

 

Dietary Reference Intake

Not Attaining (%)

Mineral

RDA

EAR or AI

RDA

EAR or AI

Calcium

 

1,000 mga

 

50a

Copper

900 mg

700 mg

5

0

Iron

8 mg

6 mg

10

0

Magnesium

400–420 mg

350 mg

50

50

Selenium

55 mg

45 mg

0

0

Zinc

11 mg

9.4 mg

20

10

NOTE: The percentage of men not attaining the RDA/EAR/AI has been assessed using the US national survey intake data found in the appendices of the source below. An RDA is set from an EAR; calcium does not have an EAR therefore also no RDA. AI = Adequate Intake; EAR = Estimated Average Requirement; RDA = Recommended Dietary Allowance.

aIndicates the value is an AI rather than an EAR.

SOURCE: IOM (1997, 2000b, 2001).

sium intakes of male marine engineers fed standard rations were less than the recommended amounts (Tharion et al., 2000). The addition of hot meals to standard rations, compared with provision of only standard rations, promoted adequate mineral intakes for the soldiers (Thomas et al., 1995). However, feeding a customized, high-carbohydrate diet, compared with standard rations, during training in a hot, humid environment decreased the proportion of elite male soldiers with inadequate intakes of calcium (50 versus 95 percent) but not magnesium (75 versus 75 percent) or zinc (20 versus 25 percent) (personal communication, S. Montain, USARIEM, August 9, 2004; Savannah Ranger Study, 1996). Male hospital personnel were studied during operational training to compare the effects of meal-based versus standard rations on the resulting adequacy of mineral intakes (Baker-Fulco et al., 2002). Compared with the standard ration, the high-carbohydrate, meal-based ration was associated with more soldiers consuming adequate calcium, similar percentages consuming adequate magnesium, but fewer consuming adequate zinc (Table B-8). Thus, magnesium, zinc, and calcium intake levels are limited in civilian and military men, and data on copper and selenium in soldiers are lacking.

FUNCTIONAL RESPONSES TO DIFFERENCES IN MINERAL INTAKES

Mineral intakes affect human biological functions. Controlled studies of restriction and supplementation of mineral intakes reveal deficits and enhance-

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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TABLE B-8 Male Hospital Workers During Training Consumptiona of Limiting Minerals

Mineral

Dietary Plan

Concept

MRE XVII

Calcium

31

44

Iron

0

2

Magnesium

38

43

Zinc

100

21

NOTE: MRE = Meal, Ready-to-Eat.

aPercentage of soldiers consuming less than 70 percent of the military standards for adequacy of nutrient intake.

SOURCE: Baker-Fulco et al. (2002).

ments, respectively, in measures of physiological and psychological function and performance.

Zinc

Zinc is required for the structure and activity of more than 300 enzymes (Vallee and Falchuk, 1993). Because zinc functions in all physiological systems, adequate zinc status is needed for optimal physiological and psychological performance.

Low zinc status impairs muscle and cardiorespiratory functions (Table B-9). Adolescent gymnasts with decreased serum zinc concentrations, compared with age-matched, nonathletic controls, experienced reduced muscle strength (Brun et al., 1995). Male athletes with low, in contrast with normal, serum zinc concentrations had decreased power output (physical work capacity, watts) and increased blood lactate concentrations during peak exercise tests (Khaled et al., 1997).

Controlled feeding studies with low zinc intakes show adverse physiological function. Men fed severely zinc deficient diet (< 1 versus 12 mg/day of zinc) had decreased muscle strength and work capacity (Van Loan et al., 1999). Physically active men fed a moderately low zinc diet (5 versus 18 mg/day) had impaired cardiorespiratory function during peak and prolonged submaximal exercise (Lukaski, 2005).

Low zinc intakes and status have been related to deficits in memory, perception, attention, and motor skills, while zinc supplementation has improved memory (Table B-10). Low serum zinc in otherwise well-nourished men fed 5, compared with 15, milligrams per day of zinc was associated with faster, but less accurate, performance on memory for digits and several perceptual tasks (Tucker and Sandstead, 1984). Contrasted to a control period when men were fed adequate zinc (10 mg/day), low zinc intakes (1, 2, 3, or 4 mg/day) resulted in

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

TABLE B-9 Effects of Selected Minerals on Measures of Physical Function and Performance

Mineral

Subjects

Study Design

Outcome

Reference

Zinc

Adolescents

Observation

↓Strength

Brun et al., 1995

Men

Observation

↓Power

Khaled et al., 1997

Men

5 vs. 18 mg/day

a↓Aerobic capacity, ↑Ventilation, ↑HR

Lukaski, 2005

Men

<1 vs. 12 mg/day as zinc sulfate

a↓Strength

Van Loan et al., 1999

Magnesium

Men

+250 mg/day as magnesium oxide

b↑Endurance, ↓Oxygen use

Brilla and Gunther, 1995

Men

+250 mg/day as magnesium oxide

b↑Strength

Brilla and Haley, 1992

Men

+370 mg/day as magnesium pidolinate

b↓Oxygen use, ↓Lactate

Golf et al., 1994

Copper

Men

0.9 vs. 2 mg/day as copper amino acid chelate

b↑Oxygen use, ↑HR, ↑Lactate, ↓Muscle cytochrome c oxidase activity

Lukaski and Johnson, 2005

Iron

Women

+100 mg/day as ferrous sulfate

↑Training

Brownlie et al., 2002

Women

+100 mg/day as ferrous sulfate

↑Strength

Brutsaert et al., 2003

Women

+100 mg/day as ferrous sulfate

↓Time trial

Hinton et al., 2000

NOTE: See text for details.

aEffect of lower, compared with higher, intake.

bEffect of supplement.

decreased performance on psychomotor (tracking and connect-the-dots), attention (orienting and misdirection), memory (letter, shape, and cube recognition), perceptual (search-count), and spatial (maze) tasks. However, there was no evidence of a “dose–response” effect of dietary zinc on cognitive performance (Penland, 1991). Reaction times during word recall were significantly slower when men were fed low amounts of zinc (5 versus 14 mg/day) (Kretsch et al., 2000).

Magnesium

Magnesium, a cofactor in more than 300 enzyme reactions in which food is metabolized and new products are formed, regulates many biological functions (Shils, 1997). Thus, it is a potentially limiting nutrient for human performance.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

TABLE B-10 Effects of Selected Minerals on Measures of Psychological Function and Performance

Mineral

Subjects

Study Design

Outcome

Reference

Zinc

Men

5 vs. 15 mg/day

a↓Memory, ↓Perception

Tucker and Sandstead, 1984

Men

5 vs. 14 mg/day

↓Memory

Kretsch et al., 2000

Men

1, 2, 3, 4 vs. 10 mg/daya

a↓Psychomotor, ↓Attention, ↓Perception, ↓Memory

Penland, 1991

Magnesium

Men

Observation

↓EEG alpha

Delorme et al., activity 1992

Copper

Women

1 vs. 3 mg/day

a↑Sleep time, ↑Confusion, ↑Latency to sleep, ↑Depression, ↓Feeling rested

Penland, 1988

Women

1 vs. 3 mg/day

a↓Short-term memory, ↑Distraction

Penland et al., 2000

Iron

Women

+90 mg/day of ferrous fumarate

b↑Attention, ↑Memory

Groner et al., 1986

Women

Not reported

↑Learning, ↑Memory

Murray-Kolb et al., 2004

Women

5 vs. 15 mg

a↑Sleep duration, ↑Awakenings

Penland, 1988

Men

Not reported

↓Alertness, ↓Visual detection

Tucker et al., 1981, 1982, 1984

Selenium

Women

+100 mg/day

b↓Anxiety, ↓Depression

Benton and Cook, 1991

Men

30 vs. 230 µg/day

b↓Confusion, ↓Depression

Penland and Finley, 1995

↑Positive mood

Finley and Penland, 1998

NOTE: See text for details.

aEffect of lower, compared with higher, intake.

bEffect of supplement.

The dietary restriction of magnesium reduced the magnesium status and impaired physiological function and performance in untrained adults. As shown in Table B-9, physically active men supplemented with magnesium (250 mg/day for four weeks) experienced increased endurance and decreased oxygen use during submaximal exercise (Brilla and Gunter, 1995).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

Supplementation with magnesium salts improved cellular function. Men receiving 370 mg of magnesium daily for four weeks had reduced serum lactate concentration and oxygen uptake during a progressive rowing test (Golf et al., 1994). Magnesium supplementation (250 mg/day for seven weeks) increased muscle strength and power in men participating in a strength training regimen (Brilla and Haley, 1992). Although modest strength gains occurred with magnesium intakes of 540 mg/day (290 mg from diet and 250 mg from supplements), increases were achieved at intakes greater than the RDA of 420 mg/day (IOM, 1997).

Whereas severe magnesium deficiency has been associated with numerous neurological and psychological disturbances (Dubray and Rayssiguier, 1997), few reports have described neuropsychological effects from marginal magnesium restriction (Delorme et al., 1992; Table B-10). Male athletes with low, compared with normal, erythrocyte magnesium had significantly less alpha activity in the right occipital region as recorded by an electroencephalogram (EEG) (Delorme et al., 1992), which suggests that magnesium is involved in regulating cortical activity related to motor function.

Copper

Copper is a cofactor of many metalloenzymes and, thus, copper status may affect diverse biological functions. It regulates iron absorption, neurotransmitter metabolism, antioxidant defense, and oxygen use. Longitudinal studies of diet and physical training showed an adaptation in antioxidant protection (Table B-9). Collegiate swimmers training for competition increased dietary copper from 1 to 1.4 mg/day, resulting in an increased erythrocyte superoxide dismutase activity and no change in plasma copper, whereas nontraining control subjects did not change enzyme activity at the same intakes of copper (Lukaski et al., 1989, 1990). Adequate copper intake is needed for adaptation in antioxidant protection during physical training.

Marginal copper intake reduces energy metabolism. Men fed less (0.9 versus 1.6 mg/day) dietary copper showed increased oxygen use, heart rate, and postexercise lactate concentrations during submaximal exercise (Lukaski and Johnson, 2005). Muscle cyctochrome c oxidase activity decreased with the marginal dietary copper (Table B-9). Thus, restricted copper intake appears to increase energy use during low-level work.

Many of the studies to measure cognition and behavioral effects of copper deficiencies have been conducted with women. Restricted dietary copper has been associated with impaired verbal memory, and disrupted sleep and mood states in women (Table B-10). Increased sleep times, longer latency to sleep, and feeling less rested upon awakening as well as increased confusion, depression, and total mood disturbances were reported when dietary copper was low (0.8 versus 2 mg/day) (Penland, 1988). Short-term memory and immediate recall of verbally presented words (list recall) worsened with low dietary copper (1 versus

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

3 mg) (Penland et al., 2000). Low copper intakes were also associated with increased difficulty in discriminating between relevant and irrelevant responses. Sufficient plasma copper and ceruloplasmin are associated with improved verbal and long-term memory, increased clustering of verbal material (strategy), and fewer distractions (Penland et al., 2000).

Iron

Iron is needed to deliver oxygen to tissues and to use oxygen at the cellular level. It serves as a functional component of iron-containing proteins needed for efficient energy use as well as for catecholamine metabolism.

Whereas the adverse effects of iron deficiency anemia on work capacity and endurance are well established (Tobin and Beard, 1997), there is growing interest in the functional effects of tissue iron depletion without anemia. Iron deficiency anemia in men is rare, except with excessive blood loss. Estimates of tissue iron depletion in men range from 5 to 15 percent despite only a 5 percent prevalence of low iron intake (IOM, 2001). Accumulating evidence shows that a low-iron status without anemia (e.g., low serum ferritin or transferrin saturation) elicits impaired physical performance, including time used to complete standard running distance (Hinton et al., 2000), endurance training adaptation (Brownlie et al., 2002), and muscle function (Brutsaert et al., 2003) that are all ameliorated with increased iron intake.

Male soldiers participating in Ranger training maintained normal hematology with increased ferritin and decreased serum iron (Shippee, 1993). Various measures of muscle strength and endurance decreased with the training. Because food intake as well as body and fat-free mass concomitantly decreased, one may conclude that reduced iron status contributed to the impaired physical performance.

Iron status has been related to attention, memory, and learning. Iron supplementation in young women (180 mg/day for 30 days) improved attention and short-term memory (Groner et al., 1986), while verbal learning and memory improved significantly in nonanemic, iron-deficient women supplemented similarly with iron (Bruner et al., 1996). Accuracy and reaction times on tasks measuring attention, memory, and learning were improved in women with the highest, compared with the lowest, ferritin and transferrin saturation in the absence of anemia (Murray-Kolb et al., 2004).

Sleep and mood disturbances have been related to dietary iron restriction. Nonanemic women and menstruating women fed low dietary iron (5 versus 15 mg/day) reported more frequent night-time awakenings and more total sleep duration (Penland, 1988). This low iron intake also increased reports of depression, fatigue, and total mood disturbances (Penland, 1989).

Select patterns of cortical activity (measured by EEG) have been predicted by iron status in nonanemic men. Consistent with depressed alertness, lower serum iron and ferritin were associated with more low-frequency EEG activity

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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and lower amplitude-evoked potentials in response to visual stimuli (Tucker and Sandstead, 1981; Tucker et al., 1982, 1984).

Selenium

Selenium acts through its association with proteins as an antioxidant and a regulator of thyroid hormone metabolism. The independent role of selenium in exercise performance and metabolism is not well understood because of its interdependence with vitamin E and other nutrients in antioxidant defense.

Endurance-trained men supplemented with selenium (180 µg/day as selenomethionine versus a placebo) significantly increased plasma selenium and glutathione peroxidase activity with no effect on performance (Tessier et al., 1995b). Improvements in peak oxygen uptake were significantly correlated with glutathione peroxidase activity only in the men supplemented with selenium. Young men supplemented with 240 µg/day of selenium (selenomethionine) and trained for endurance had no performance benefit but a significant increase in muscle glutathione peroxidase activity (Tessier et al., 1995a). Thus, supplemental selenium upregulates biochemical markers of selenium status without enhancing performance.

Several studies have shown an effect of selenium intakes and status on mood states in both men and women (Table B-10). Women and men supplemented with selenium (100 µg/day) reported less anxiety and depression and more energy (Benton and Cook, 1991). Men fed supplemental selenium (230 versus 30 µg/day) reported less confusion and depression (Penland and Finley, 1995). Activity of glutathione peroxidase, a selenium enzyme, in platelets was positively correlated with all mood states (Finley and Penland, 1998).

Calcium

Although its role in bone metabolism is emphasized, calcium acts in mediating vascular, muscular, and nerve functions. Adverse effects of inadequate calcium intake on physical performance are not well studied. However, calcium is required to regulate glycolysis and glycogenolysis and to control protein breakdown. Studies of the effects of calcium restriction or supplementation on human metabolism are lacking despite evidence that calcium intake for 50 percent of adult men is less than the AI (IOM, 1997).

DIETARY INTAKE, NUTRITIONAL STATUS, AND PERFORMANCE IN FIELD STUDIES

Military personnel participating in training and operational exercises consistently decrease food intake, thus consuming inadequate amounts of minerals. Blood biochemical markers of nutritional status, however, do not reveal overt

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

mineral deficiencies although assessments of hormonal and immune functions show decreases (Booth et al., 2003; Shippee, 1993). Failure to detect nutritional deficiencies is explained by a lack of sensitive biochemical markers of mineral status, brief durations of restricted intakes, and mineral mobilization from stores into the blood with increased metabolic demands and loss of body weight.

Measurable impairments in aerobic capacity or muscle power occur when body weight decreases about 10 percent with a 5 percent loss in muscle mass (Friedl, 1995). Cognitive function declines when significant weight loss (> 6 percent) occurs (Mays, 1995). When energy restriction (50 percent decrease) occurs with strenuous activity, sleep deprivation and mental stress, cognitive performance may fall by more than 33 percent within a few days (Mays, 1993). Decreased food intake plus physical and mental stressors for 12 days increase reports of fatigue and sleep impairment, even at modest levels of weight loss (3 percent) (Booth et al., 2003). Thus, brief and prolonged periods of exposure to nutritional, environmental, physical, and mental stressors impair cognitive performance, including attention, perception, memory, and reasoning (Mays, 1993).

Some reports describe decreased nutritional status during military operations. Shippee (1993) found decreased iron and altered copper and zinc status in Ranger II. Also, Booth and colleagues (2003) reported a decline in iron status in both 12- and 23-day training activities. It is unclear if these findings reflect a response to stress and inflammation or to inadequate intakes of these minerals.

Repeated assault operations may result in mineral depletion because of inadequate intake, and increased turnover and losses of minerals may promote marginal deficiencies under stressful conditions. Also, entry into operations with marginal mineral status may predispose individuals to deficiency status and functional deficits, particularly with repetitive assaults without replenishment of depleted mineral reserves.

FOOD QUALITY AND NUTRIENT DENSITY

Replacing standard combat rations with fresh food and hot meals may alleviate the adverse effects on body weight, physical performance, and cognitive function (Booth et al., 2003; Tharion et al., 2004). This approach, however, is not feasible for soldiers in assault operations. Therefore, new strategies are needed to provide soldiers with proper nutrition.

One approach is to increase the nutrient density of assault rations. Mineral nutrient densities should meet the military standards for reduced-energy rations for men (Baker-Fulco et al., 2001; US Departments of the Army, Navy, and Air Force, 2001). Thus, with reduced energy intake, soldiers would still have adequate mineral intakes.

Steps to improve food intake should be further explored (Hirsch and Kramer, 1993). These include adding new, fortified foods and using stages of change

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

models to foster healthful nutrition habits (Veverka et al., 2003). Increasing emphasis on maintaining adequate hydration and sleep, particularly during recovery periods, will support these efforts.

Active efforts to prevent marginal mineral depletion should be employed. Some suggestions include:

  • Develop and support an active nutrition education program.

  • Provide palatable, mineral-rich food items in the rations, including on-the-go foods.

  • Increase the availability of mineral-rich foods during recovery periods.

  • Encourage unit leaders and peers to be models of healthful eating behaviors.

SUMMARY AND CONCLUSIONS

Evidence shows that military personnel fail to consume adequate amounts of magnesium, zinc, and calcium. These minerals, as well as copper, selenium, and iron, play key roles in promoting optimal physiological and psychological function and performance. Limited data on mineral intakes and the resulting status of soldiers in various types of training do not provide evidence of overt nutritional deficiencies. A lack of sensitive biochemical markers of nutritional status hinders interpretation of available data. It is difficult to discriminate the independent effect of severely restricted energy intake on potential micronutrient impairments. Nevertheless, physiological and psychological impairments found in civilians with marginal mineral deficits are consistent with perturbations reported in soldiers during operations and suggest similarities, particularly when the low mineral intakes have been noted in the soldiers.

Based on limited evidence of inadequate intakes of zinc and magnesium, and the presumption of increased zinc losses associated with increased physical activity and elevated rates of sweat, zinc and magnesium status may be compromised. With repeated bouts of these conditions and inadequate replenishment of zinc and magnesium stores, soldiers may manifest marginal zinc and magnesium depletion and experience limitations in work capacity, recovery after deployment, perception, and attention. Furthermore, zinc depletion may attenuate immune function and increase the potential for acute bouts of gastrointestinal distress. Evidence of reduced antioxidant defense is generally lacking in military personnel during short-term assault missions. However, recurrent intermittent periods of inadequate intakes of copper, selenium, zinc, and manganese without adequate intakes during recovery may lead to decreased activity of protective antioxidant enzymes.

Generalized use of multiple vitamin and mineral supplements at intakes not exceeding recommended levels should not be hazardous to soldiers participating in assault missions. The use of single nutrient supplements in amounts exceeding

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

the recommended intake should be avoided to eliminate potential adverse interactions with other nutrients, particularly mineral elements.

Initiating a proactive approach to decrease the potential of adverse effects of limited mineral intakes is recommended. Increasing the mineral densities of assault rations should be advantageous. Adopting an active nutrition education program with palatable, mineral-rich foods and encouraging leaders to model healthy eating behaviors also should be useful to reverse the high rates of low-mineral intakes of soldiers.

RESEARCH NEEDS

There is a need to determine the nutrient intakes, markers of nutritional status, and physiological and psychological performance of military personnel during training and operations. This information is needed to critically evaluate the adequacy of rations provided to and consumed by soldiers exposed to multiple stressors. Findings of this research will enhance the development of rations that promote optimal nutrition and, accordingly, the performance of soldiers engaged in assault operations.

ACKNOWLEDGMENTS

Mention of a trademark or proprietary product does not constitute a guarantee of the product by the US Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable. US Department of Agriculture, Agricultural Research, Northern Plains Area, is an equal opportunity/affirmative action employer and all agency services are available without discrimination.

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Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Effect of Inadequate B Vitamin Intake and Extreme Physical Stress

Lynn B. Bailey and Kristina von Castel-Dunwoody, University of Florida

INTRODUCTION

The primary objective of this paper is to evaluate the potential effect of inadequate B vitamin intake in relation to the consumption of assault rations under extreme physical stress during intense military combat operations. The goal is to characterize the optimal B vitamin content for future rations that will be designed to maximize the physical and mental performance of soldiers

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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engaged in intensely stressful combat operations. The specific questions that were posed by the Committee on Optimization of Nutrient Composition of Military Rations for Short-Term, High-Stress Situations are the following:

  • What are the types and levels of B vitamins and choline that could be added to such rations to enhance performance and/or improve recovery during combat missions?

  • Does exercise increase B vitamin use? Does decreased energy intake impact this? Will supplementation regardless of energy level meet B vitamin requirement during exercise?

  • Do B vitamins and choline affect the bioavailability of other nutrients?

The current ration is hypocaloric in that it provides approximately 2,400 kcal for an expected energy expenditures of 4,000 to 4,500 kcal/day. The B vitamin content of the assault ration has not been analyzed chemically; however, the ration is designed to meet the nutrition standards of a restricted energy ration in which the vitamin content is proportionally reduced with the energy content. The estimated B vitamin content of the current assault ration is as follows: (1) thiamin, 0.6 mg; (2) riboflavin, 0.7 mg; (3) niacin, 8 mg NE; (4) vitamin B6, 0.7 mg; (5) folic acid, 200 µg dietary folate equivalents (DFE); and (6) vitamin B12, 1.2 µg [personal communication, S. Montain, USARIEM, July 16, 2004)]. These estimated quantities are approximately 50 percent of the Recommended Dietary Allowance (RDA) or Adequate Intake (AI) for young adult males (IOM, 1998); therefore, the current ration is both hypocaloric and deficient in B vitamin content (Table B-11). This paper presents examples of data supporting the conclusions

TABLE B-11 Dietary B Vitamins in a Ration Compared with the RDA or AI for Men Ages 19 to 30 Years

Vitamin

Estimated B Vitamin Content in Current Ration

RDA or AI

Thiamin

0.6 mg

1.2 mg

Riboflavin

0.7 mg

1.3 mg

Niacin

8 mg NE

16 mg NE

Vitamin B6

0.7 mg

1.3 mg

Folic Acid

200 µg

400 µg DFE

Vitamin B12

1.2 µg

2.4 µg

Biotin

30 µga

Pantothenic Acid

5 mga

NOTE: AI = Adequate Intake; DFE = dietary folate equivalents; NE = niacin equivalents; RDA = Recommended Dietary Allowance.

aIndicates the value is an AI rather than a RDA.

SOURCE: IOM (1998); personal communication, S. Montain, USARIEM, July 16, 2004.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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that (1) inadequate B vitamin intake and caloric restriction impair physical and cognitive performance, and (2) extreme physical exertion coupled with caloric restriction significantly increases the requirement for B vitamins.

THE EFFECT OF INCREASED ENERGY DEMAND ON B VITAMIN USE

The B vitamins are required coenzymes for energy production in hundreds of metabolic reactions, including those required for glycolysis, the citric acid cycle, β-oxidation, amino acid metabolism, glycogenolysis, and gluconeogenesis (Bowman and Russel, 2001). Evidence suggests that when energy needs are increased by physical exertion, the B vitamin requirement increases to sustain energy production and maintain normal vitamin status.

Van der Beek and colleagues (1988) investigated the effect of low B vitamin intake on vitamin status and physical performance. These investigators conducted an eight-week, double-blind, controlled metabolic study in healthy young adult males (n = 24) described as moderately active. The study compared the effect of consumption of a diet low in thiamin, riboflavin, and vitamin B6 with that of a deficient diet plus a supplement providing twice the Dutch RDA for these B vitamins. (2.5 mg, 4 mg, and 4 mg, respectively). The quantities of dietary B vitamins in the low vitamin group were similar to the quantities in the current military assault rations (i.e., 0.42 mg/day of thiamin; 0.53 mg/day of riboflavin; and 0.32 mg/day of vitamin B6). The subjects consuming the low B vitamin diet were supplemented with twice the Dutch RDA for all vitamins except thiamin, riboflavin, and vitamin B6 during the eight-week period of low vitamin intake. Unlike the combat ration, both experimental diets contained adequate calories (3,070 kcal/day).

Thiamin status was determined by measuring thiamin diphosphate concentration (TDP) and erythrocyte transketolase (ETK) activity as well as its in vitro stimulation by TDP (α-ETK or activation coefficient). Riboflavin status was assessed by means of flavin adenine dinucleotide (FAD) and erythrocyte glutathione reductase (EGR) activity as well as its in vitro stimulation by FAD (α-EGR). Vitamin B6 status assessment was based on pyridoxal-5′-phosphate (PLP, the active form of the vitamin) concentration and erythrocyte glutamate oxaloacetate (EGOT) activity as well as its in vitro stimulation by PLP (α-EGOT). Within three to six weeks, deterioration of the vitamin status was indicated by decreased B vitamin coenzyme concentrations in blood, decreased erythrocyte enzyme activities, and elevation of stimulation tests of these enzymes, indicating an insufficient supply of coenzyme to maintain normal enzyme activity.

Physical performance was quantified by means of submaximal and maximal oxygen consumption (VO2max). The onset of blood lactate accumulation (OBLA) was measured as well. To determine VO2max and OBLA, the subjects performed incremental bicycle exercise tests. Both the aerobic power and maxi-

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

FIGURE B-21 Effect of combined low B vitamin intake on aerobic power (A) and work capacity (B). This effect is illustrated by the change of maximal performance from the baseline to 10 weeks during the study.

*Significantly different compared to control at p < 0.01.

SOURCE: van der Beek et al. (1988).

mal workload were significantly lower in the low vitamin group than in the control group (Figure B-21). The blood lactate concentration increase occurred at a lower intensity of physical exertion in the low vitamin group than in the control group. In summary, consumption of a diet adequate in calories but low in thiamin, riboflavin, and vitamin B6 resulted in significantly impaired biochemical

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

FIGURE B-22 Effect of exercise on riboflavin requirement in men.

NOTE: EGRAC = erythrocyte glutathione reductase activation coefficient.

*Significantly different compared to control (nonexercise) at p < 0.05.

SOURCE: Soares et al. (1993).

status, impaired aerobic power, decreased work capacity, and increased blood lactate at a lower intensity of work.

Soares and colleagues (1993) evaluated the effect of exercise on the riboflavin status of adult men whose baseline riboflavin status was inadequate. Energy balance was maintained throughout the study. Riboflavin status, based on increases in the erythrocyte glutathione reductase activation coefficient (EGRAC), deteriorated significantly and the impaired status persisted during the subsequent recovery period when the study participants exercised (Figure B-22). These data indicate that riboflavin status further deteriorates during a short period of increased physical activity in individuals whose riboflavin status is marginal.

As reviewed by Manore (2000), the results of a number of controlled metabolic studies in women indicate that exercise, dieting for weight loss, or a combination of both all increase riboflavin requirements. In one study by Belko and colleagues (1983), young women consumed various amounts of riboflavin over a 10-week period, and their EGRAC values were determined. The EGRAC values were above the cutoff of 1.25, indicating poor riboflavin status during the first two weeks, when they consumed 0.14 mg of riboflavin/MJ (239 kcal). In response to the consumption of 0.24 mg/MJ during the second two-week period, the EGRAC values returned to normal. For the next three weeks, the riboflavin intake was 0.24 mg/MJ, and the women started to exercise (20 to 50 minutes, six days a week). The initiation of exercise increased the mean EGRAC values above the cutoff. During the last three weeks, the women continued to exercise, and their riboflavin intake increased to 0.33 mg/MJ. At this higher riboflavin

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

intake, the mean EGRAC values were normal, indicating that exercise led to an increase in the riboflavin requirement.

In two other metabolic studies, Belko and colleagues (1984, 1985) examined the effect of energy restriction and energy restriction plus physical exertion on riboflavin status. Overweight women consumed a metabolic diet that provided 1,195 to 1,266 kcal/day and various quantities of riboflavin (0.14 to 0.19 mg/MJ). The amount of riboflavin required to maintain good status was increased by energy restriction and increased even more by energy restriction plus exercise. It was concluded that a 0.38 mg/MJ level of riboflavin is required to keep EGRAC values in the normal range when female subjects dieted and exercised three to four hours week at 75 to 85 percent of the maximal heart rate.

The effect of exercise and energy restriction on riboflavin status was also evaluated by Winters and colleagues (1992), who fed older female subjects (50 to 67 years old) a metabolic diet that contained adequate calories to maintain weight and either 0.15 or 0.22 mg/MJ of riboflavin for five weeks. During the period when no exercise was performed, EGRAC values increased significantly. When subjects were exercising, 0.22 mg/MJ was required to maintain mean EGRAC values within the normal range. The conclusion from this investigation was that while energy restriction alone or exercise alone may increase riboflavin requirements above the RDA, calorie restriction plus exercise increases the requirement even more.

Manore and colleagues (1987) evaluated the effect of exercise on vitamin B6 status. Plasma PLP concentrations increased significantly in response to exercise and returned to baseline within 60 minutes after exercise stopped (Figure B-23). The marked increase in plasma PLP in response to exercise increases the probability that the active coenzyme form of the vitamin (PLP) may be metabolized to the major excretory form (4-pyridoxic acid) and lost in the urine (Crozier et al., 1994). It has been proposed, therefore, that exercise may increase the turnover and loss of vitamin B6 in active individuals.

In addition, Fogelholm and colleagues (1993) evaluated the effect of energy restriction coupled with exercise on vitamin B6 status. A diet (1,673 kcal/day) consumed by elite male wrestlers over a three-week period resulted in a significant increase in vitamin B6-dependent enzyme stimulation. Since no dietary intake data were obtained, there is a possibility that poor vitamin B6 dietary intake may have also contributed to the impairment of vitamin B6 status. In a different study, van Dale and colleagues (1990) compared the vitamin B6 status in two groups of obese adult males who consumed low-calorie diets (716–931 kcal/day) for 14 weeks. In the group that consumed the weight-reduction diet coupled with exercise, plasma PLP concentration decreased from 54 to 40 mmol/L, but no such change occurred in the group who consumed the same diet but did not exercise. In addition, riboflavin status was also decreased in the diet-plus-exercise group.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

FIGURE B-23 Changes in a blood coenzyme form of vitamin B6 (PLP) in response to very moderate exercise.

NOTE: PLP = pyridoxal 5′-phosphate.

*Sgnificant increase from baseline to immediately after exercise at α = 0.05 level.

**Significant decrease from immediately after exercise to 60 minutes after exercise at α = 0.05 level.

SOURCE: Manore et al. (1987).

EFFECT OF LOW B VITAMIN INTAKE ON MENTAL PERFORMANCE

The B vitamins are essential for normal neurological function. Deficiencies of vitamin B6 and thiamin result in rapid neurological abnormalities (McCormick, 2001; Wood and Currie, 1995). The synthesis of key neurotransmittors, including serotonin, dopamine, norepinephrine, and γ-amniobutyric acid, is dependent on an adequate supply of vitamin B6. Thiamin is required for normal neural cell function with different mechanisms of action proposed for normal nerve cell function (Bates, 2001). Folate is also required for the synthesis of a number of different neuroactive substances through its role as a methyl group donor (Bottiglieri, 1996). In addition, folate is a required coenzyme for homocysteine remethylation; low folate intake results in elevated homocysteine concentrations that have been associated with excitotic properties (Fava et al., 1997).

The effect of a low intake of thiamin (0.42 mg/day), riboflavin (0.53 mg/day), and vitamin B6 (0.32 mg/day) on mental performance was evaluated in an eight-week double-blind controlled study in healthy young adult males (van der Beek et al., 1988). The mental performance test results indicated that subjects who

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

consumed the low B vitamin diet made more errors (described as displaying a more risky behavior) and needed more time to complete tasks than subjects consuming the control diet, which contained twice the Dutch RDA (2.5 mg/d thiamin, 4 mg/day riboflavin and vitamin B6) for these substances.

Low folate status has been associated with depression, cognitive dysfunction, psychosocial disorders, insomnia, irritability, impaired memory, and fatigue (Alpert et al., 2000; Bottiglieri et al., 1995). A meta-analysis of randomized controlled trials suggests that folate may have a potential role as a supplement to other treatments for depression (Taylor et al., 2004). Table B-12 includes a summary of studies that evaluated the association between folate status and mental performance.

TABLE B-12 Studies on Folate Levels and Mental Status

Authors

Subjects

Folate

Goodwin et al., 1983

Healthy noninstitutionalized, compared top 10% with bottom 5% and 10%

Lower concentration associated with lower test scores (p < 0.01) (Halstead-Reitan Categories Test)

Joosten et al., 1997

AD patients (A); Hospitalized control subjects (B); Healthy elderly (C)

Blood concentration significantly lower in A versus C (p < 0.04)

Kristensen et al., 1993

Patients with AD (A), other dementia (B), and mental disorders (C). Control subjects (D)

Blood concentration significantly lower in A versus D (p < 0.05)

Levitt and Karlinsky, 1992

AD patients and controls

Blood concentration significantly lower in subjects (p > 0.05)

Nilsson et al., 1996

Neuropsychiatric dementia patients (A); Neuropsychiatric patients no dementia (B); Control patients (C)

Blood concentration significantly lower in A versus B and C (p < 0.001)

Renvall et al., 1989

AD patients and normal individuals (A); Dementia patients and normal patients (B)

Blood concentration significantly lower in A (p > 0.03) and B (p < 0.05)

Riggs et al., 1996

Male volunteers

Lower concentration associated with lower test scores (p = 0.003) (Spatial copying test)

NOTE: AD = Alzheimer’s disease.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

RESPONSE TO SPECIFIC QUESTIONS RELATED TO REVISING THE B VITAMIN CONTENT OF THE PROPOSED MILITARY COMBAT RATION

A key question related to formulation of the proposed military ration is whether increasing the B vitamin content will enhance the performance of combat soldiers. The current combat ration is hypocaloric and estimated to have approximately 50 percent of the RDA for the B vitamins (personal communication, S. Montain, USARIEM, July 16, 2004). Data from the controlled studies reviewed above support the conclusion that increasing the B vitamin content in the current combat ration will likely enhance the physical and mental performance of soldiers. The studies consistently indicate that either exercise or energy restriction will increase the requirement of select B vitamins, and combining physical exertion with energy restriction will decrease B vitamin status and performance.

A second key question is whether the energy content of the combat ration should be maximized to reduce the energy debt. Based on findings from the controlled metabolic studies discussed above, energy restriction alone will result in impaired B vitamin status. There are no data that support the conclusion that supplemental B vitamins will compensate for all of the metabolic changes that occur due to energy restriction, but to maintain the B vitamin status, it is recommended that the B vitamins be added to the diet in excess of the RDA.

SUMMARY AND CONCLUSIONS

Energy restriction or moderate exercise increases the body’s use of B vitamins to maintain metabolic pathways involved in energy production. A combination of energy restriction and moderate exercise increases B vitamin use to an even greater extent. In contrast to the short, intermittent periods of moderate exercise evaluated in the controlled studies, the intensity and duration of physical exertion during military combat operations are much greater and sustained for much longer periods. It is logical to assume that the effect of energy restriction and extreme physical exertion on B vitamin metabolism would be exacerbated during military combat. The recommended B vitamin content of the proposed new combat ration is twice the current RDA (Table B-13). For the B vitamins and choline not considered in this review, it is also recommended that the ration contain twice the RDA or AI (Table B-13).

REFERENCES

Alpert JE, Mischoulon D, Nierenberg AA, Fava M. 2000. Nutrition and depression: Focus on folate. Nutrition 16(7–8):544–546.


Bates CJ. 2001. Thiamin. In: Bowman BA, Russell RM, eds. Present Knowledge in Nutrition. Washington, DC: ILSI Press. Pp. 184–190.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

TABLE B-13 Suggested B Vitamin Content for the Ration

Vitamin

RDA or AI Doubled for Daily Intake

Thiamin

2.4 mg

Riboflavin

2.6 mg

Niacin

32 mg NE

Vitamin B6

2.6 mg

Folate

800 µg DFE (475 mg folic acid × 1.7)

Vitamin B12

4.8 µg

Biotin

60 µga

Pantothenic Acid

10 µga

Choline

1,100 mga

NOTE: AI = Adequate Intake; DFE = dietary folate equivalents; NE = niacin equivalents; RDA = Recommended Dietary Allowance.

aIndicates the value is an AI rather than a RDA.

SOURCE: IOM (1998).


Belko AZ, Meredith MP, Kalkwarf HJ, Obarzanek E, Weinberg S, Roach R, McKeon G, Roe DA. 1985. Effects of exercise on riboflavin requirements: Biological validation in weight reducing women. Am J Clin Nutr 41(2):270–277.

Belko AZ, Obarzanek E, Kalkwarf HJ, Rotter MA, Bogusz S, Miller D, Haas JD, Roe DA. 1983. Effects of exercise on riboflavin requirements of young women. Am J Clin Nutr 37(4):509–517.

Belko AZ, Obarzanek E, Roach R, Rotter M, Urban G, Weinberg S, Roe DA. 1984. Effects of aerobic exercise and weight loss on riboflavin requirements of moderately obese, marginally deficient young women. Am J Clin Nutr 40(3):553–561.

Bottiglieri T. 1996. Folate, vitamin B12, and neuropsychiatric disorders. Nutr Rev 54(12):382–390.

Bottiglieri T, Crellin R, Renolds EH. 1995. Folates and neuropsychiatry. In: Bailey LB, ed. Folate in Health and Disease. New York: Marcel Dekker. Pp. 435–462.

Bowman BA, Russel RM. 2001. Present Knowledge in Nutrition. 8th ed. Washington, DC: ILSI Press.


Crozier PG, Cordain L, Sampson DA. 1994. Exercise-induced changes in plasma vitamin B-6 concentrations do not vary with exercise intensity. Am J Clin Nutr 60(4):552–558.


Fava M, Borus JS, Alpert JE, Nierenberg AA, Rosenbaum JF, Bottiglieri T. 1997. Folate, vitamin B12, and homocysteine in major depressive disorder. Am J Psychiatry 154(3):426–428.

Fogelholm M, Ruokonen I, Laakso JT, Vuorimaa T, Himberg JJ. 1993. Lack of association between indices of vitamin B1, B2, and B6 status and exercise-induced blood lactate in young adults. Int J Sport Nutr 3(2):165–176.


Goodwin JS, Goodwin JM, Garry PJ. 1983. Association between nutritional status and cognitive functioning in a healthy elderly population. J Am Med Assoc 249(21):2917–2921.


IOM (Institute of Medicine). 1998. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitmain B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press.


Joosten E, Lesaffre E, Riezler R, Ghekiere V, Dereymaeker L, Pelemans W, Dejaeger E. 1997. Is metabolic evidence for vitamin B-12 and folate deficiency more frequent in elderly patients with Alzheimer’s disease? J Gerontol A Biol Sci Med Sci 52(2):M76–M79.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Kristensen MO, Gulmann NC, Christensen JE, Ostergaard K, Rasmussen K. 1993. Serum cobalamin and methylmalonic acid in Alzheimer dementia. Acta Neurol Scand 87(6):475–481.


Levitt AJ, Karlinsky H. 1992. Folate, vitamin B12 and cognitive impairment in patients with Alzheimer’s disease. Acta Psychiatr Scand 86(4):301–305.


Manore MM. 2000. Effect of physical activity on thiamine, riboflavin, and vitamin B-6 requirements. Am J Clin Nutr 72(2 Suppl):598S–606S.

Manore MN, Leklem JE, Walter MC. 1987. Vitamin B-6 metabolism as affected by exercise in trained and untrained women fed diets differing in carbohydrate and vitamin B6 content. Am J Clin Nutr 46(6):995–1004.

McCormick DB. 2001. Vitamin B-6. In: Bowman BA, Russel RM, eds. Present Knowledge in Nutrition. Washington, DC: ILSI Press. Pp. 207–213.


Nilsson K, Gustafson L, Faldt R, Andersson A, Brattstrom L, Lindgren A, Israelsson B, Hultberg B. 1996. Hyperhomocysteinaemia—A common finding in a psychogeriatric population. Eur J Clin Invest 26(10):853–859.


Renvall MJ, Spindler AA, Ramsdell JW, Paskvan M. 1989. Nutritional status of free-living Alzheimer’s patients. Am J Med Sci 298(1):20–27.

Riggs KM, Spiro A 3rd, Tucker K, Rush D. 1996. Relations of vitamin B-12, vitamin B-6, folate, and homocysteine to cognitive performance in the Normative Aging Study. Am J Clin Nutr 63(3):306–314.


Soares MJ, Satyanarayana K, Bamji MS, Jacob CM, Ramana YV, Rao SS. 1993. The effect of exercise on the riboflavin status of adult men. Br J Nutr 69(2):541–551.


Taylor MJ, Carney SM, Goodwin GM, Geddes JR. 2004. Folate for depressive disorders: Systematic review and meta-analysis of randomized controlled trials. J Psychopharmacol 18(2):251–256.


van Dale D, Schrijver J, Saris WH. 1990. Changes in vitamin status in plasma during dieting and exercise. Int J Vitam Nutr Res 60(1):67–74.

van der Beek EJ, van Dokkum W, Schrijver J, Wedel M, Gaillard AW, Wesstra A, van de Weerd H, Hermus RJ. 1988. Thiamin, riboflavin, and vitamins B-6 and C: Impact of combined restricted intake on functional performance in man. Am J Clin Nutr 48(6):1451–1462.


Winters LR, Yoon JS, Kalkwarf HJ, Davies JC, Berkowitz MG, Haas J, Roe DA. 1992. Riboflavin requirements and exercise adaptation in older women. Am J Clin Nutr 56(3):526–532.

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Optimization of the Nutrient Composition in Military Rations for Short-Term, High-Stress Situations: Sodium, Potassium, and Other Electrolytes

Susan Shirreffs, Loughborough University, UK

INTRODUCTION

The specific questions addressed in this manuscript are as follows:

  1. What are the types and levels or ratios of electrolytes that could be added to such rations to enhance performance during combat missions? Specifically address the effects of environmental stress.

  2. What are the interactions between electrolytes (e.g., sodium and potassium)?

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

Certain illnesses and medications influence electrolyte balance. In this manuscript, however, dietary electrolyte requirements have not been considered for individuals with illnesses that may cause repeated vomiting, prolonged diarrhea, heat illness, or collapse or for individuals with ongoing medical treatment.

One recent publication from the Institute of Medicine (IOM, 2004) provides an up-to-date review of sodium and potassium dietary requirements. The recommendations given within this publication have been used in this manuscript as a starting point for determining a healthy diet with specific requirements for short-term, high stress situations. Adequate Intakes (AIs) were set for both sodium and potassium because an Estimated Average Requirement, and thus a Recommended Dietary Allowance could not be established.

POTASSIUM

Potassium is the major cation in the intracellular fluid, and it is maintained at a concentration of approximately 145 mmol/L; the extracellular concentration is approximately 4 to 5 mmol/L. Potassium is required for normal cellular function, and relatively small changes in the extracellular potassium can greatly affect the extra- to intracellular ratio, thereby affecting neural transmission, muscle contraction, and vascular tone.

Severe potassium deficiency, characterized by hypokalemia and indicated by a serum potassium concentration of less than 3.5 mmol/L, has consequences that include cardiac arrhythmia, muscle weakness, and glucose intolerance. Moderate potassium deficiency is characterized by increased blood pressure, salt sensitivity, and risk of kidney stones and shows evidence of increased bone turnover.

In normal circumstances, 77 to 90 percent of dietary potassium is excreted in urine with the remaining excreted in feces and sweat (Holbrook et al., 1984).

The AI for potassium set by the Panel on Dietary Reference Intakes for Electrolytes and Water (IOM, 2004) is 4.7 g (120 mmol) per day. This recommendation, however, is based on potassium intake from food, excluding supplementation, and is therefore based on forms of potassium with bicarbonate precursors. The rationale for this AI is that it should help maintain lower blood pressure levels, reduce the effects of sodium chloride intake on blood pressure, reduce the risk of kidney stones, and, possibly, decrease bone loss. The Panel assigned no Tolerable Upper Intake Level (UL) because for healthy individuals with normal kidney function, any excess dietary potassium intake from foods is excreted in the urine, feces, and sweat. However, the National Health and Nutrition Examination Survey (NHANES III, 1988–1994) in the United States indicated that the median potassium intake by male adults was approximately 2.8 to 3.3 g (72 to 84 mmol) per day. Only 10 percent of men consumed potassium in a quantity equal to or greater than the AI.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

SODIUM

Sodium is the major cation in extracellular fluid, and it is maintained at a concentration of approximately 140 mmol/L; the intracellular concentration is approximately 4 mmol/L. Along with the anion chloride, sodium maintains extracellular volume, and therefore, plasma volume and serum osmolality. It is also an important determinant of cell membrane potential and an active transporter of molecules across membranes.

In the absence of substantial sweating, individuals in sodium and water balance typically excrete 90 to 95 percent of their dietary sodium intake in their urine (Table B-14). The total obligatory sodium losses are very small, amounting to approximately 0.18 g (8 mmol) per day (Dahl, 1958).

On the basis of available data, the AI for sodium set by the Panel on Dietary Reference Intakes for Electrolytes and Water (IOM, 2004) is 1.5 g (65 mmol) per day. Based on the effects of higher sodium intake levels on blood pressure, the UL for sodium is 2.3 g (100 mmol) per day. However, while both the AI and UL were said to be appropriate for unacclimatized individuals exposed to high environmental temperatures or for people who are physically active, they were deemed inappropriate for highly active individuals or individuals who are exposed to prolonged heat and lose large amounts of sweat daily. Although the AI and UL parameters were not quantified, it is clear that the AI allows for an intake of approximately 1.3 g (57 mmol) above the maximum obligatory losses (Table B-14), meaning that this amount may be taken to accommodate increased sweat sodium loss.

Hyponatremia, which is defined as a serum sodium concentration of less than 135 mmol/L, does not generally occur with low sodium intakes (Kirkendall et al., 1976; Overlack et al., 1995), but rather is related to excessive sodium loss from the body or to excessive consumption of fluids low in sodium.

The National Health and Nutrition Examination Survey (NHANES III, 1988–1994) in the United States indicated that the median sodium intake by male adults ranged from 3.1 to 4.7 g (135 to 204 mmol) per day (IOM, 2004). This estimate, however, excludes any salt added at the table, so the intake levels

TABLE B-14 Obligatory Losses of Sodium

Source

g/day

mmol/day

Urine

0.005–0.035

0.2–1.5

Skin (nonsweating)

0.025

1.1

Feces

0.010–0.125

0.4–5.4

Total

0.040–0.185

1.7–8.0

 

SOURCE: Dahl (1958).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

may be an underestimate for many individuals. Total dietary sodium intake was recently estimated to be 4.2 g (183 mmol) per day as shown in a study that quantified intake based on 24-hour urine collections (Zhou et al., 2003).

CHLORIDE

Sodium and chloride are commonly found together in foods as sodium chloride. For this reason, and because both are commonly in association in the body, the AI for chloride set by the Panel on Dietary Reference Intakes for Electrolytes and Water (IOM, 2004) is at a level equivalent, on a molar basis, to that of sodium and thus amounts to 2.3 g (65 mmol) per day.

SODIUM-WATER INTERACTION

A brief mention of water intake is warranted because of its links with body sodium balance and sodium’s role in maintaining extracellular fluid volume. Water is the largest single constituent in the body in nonobese individuals. It acts as a solvent for biochemical reactions and as a medium of transport of other compounds, and it has a high specific heat to absorb metabolic heat, maintains vascular volume, supports the supply of nutrients, and removes waste. However, an individual’s total water intake includes drinking water, water in other drinks, and water in foods. The AI for water was established at a sufficient level to prevent the acute deleterious effects of dehydration, including functional and metabolic abnormalities. For example, the AI for total water intake for young men is 3.7 liters per day (IOM, 2004); however, higher intakes will be required for individuals who are physically active or are exposed to hot environments. In very unusual circumstances, an excess consumption of fluids combined with a low sodium intake may lead to excess body water, resulting in hyponatremia.

THE EFFECTS OF ENVIRONMENTAL STRESS ON ELECTROLYTE REQUIREMENTS

An increased environmental temperature is more physiologically stressful to free living humans than is a cold environment. Exposure to a cold environment, provided that appropriate clothing is available and, perhaps, some form of exercise to generate heat is possible, presents no special consideration with regard to electrolyte requirements. They should be no different from requirements for a “normal” environment for that individual. However, the same is not true for a warm environment because of the sweating mechanism that is activated to regulate body temperature.

When sweating it stimulated, it can have a significant influence on electrolyte losses. Sodium is the main electrolyte present in sweat, but significant amounts of other electrolytes are present (Table B-15).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

TABLE B-15 The Normal Concentration Range of Some of the Main Electrolytes in Sweat

Electrolyte

Concentration (mmol/L)

Sodium

10–80

Chloride

10–60

Potassium

4–14

Calcium

0.3–2

Magnesium

0.2–1.5

Sulfate

0.1–0.2

 

SOURCE: Costill (1977); Lentner (1981); Maughan (1991); Pitts (1959); Schmidt and Thews (1989).

Clearly, the extent of any electrolyte loss incurred will also depend on the sweat rate. As summarized by IOM (2004) when an individual is at rest and not visibly sweating, the rate of water loss through the skin is approximately 0.020 L per hour. At the other extreme, an individual that experiences shorter periods of intense activity in a warm environment could have a maximum sweat rate of 3 L per hour (Sawka and Pandolf, 1990). Other data from the literature suggest sweat rates of 0.3 to 1.2 L per hour (Adolph, 1947) for residents of desert climates performing occupational activities, while persons performing low-intensity exercise but wearing protective clothing commonly have sweat rates of 1 to 2 L per hour (Levine et al., 1990). Finally, when calculated on a daily basis from water turnover studies, sweat water losses of 0.2 to 2 L per day have been reported for sedentary individuals in a temperate climate while volumes of 1 to 9 L per day have been reported for individuals undertaking manual work or exercise in varying climates (Leiper et al., 1996, 2001; Singh et al., 1989). These very different sweat rates clearly have the potential to induce electrolyte losses, thus affecting total body electrolyte loss. Taking 0.20 L per hour (4.8 L per day) as the lowest sweat rate and 9 L per day as the highest, the losses of the main electrolytes could range as shown in Table B-16.

Many other factors, however, influence sweat composition. These include the dietary electrolyte intake (Allsopp et al., 1998; Armstrong et al., 1985b), the heat acclimation status of an individual, and the individual’s sweat rate at any time. However, as shown in Box B-2, while sodium levels are influenced by all three factors noted, divergent findings for potassium have been reported in the literature.

Many studies have attempted to quantify sodium and potassium loss through sweat and urine in a variety of settings, and some of these have been summarized in Table B-17. However, a key factor when considering dietary electrolyte intakes for groups of individuals is the vast differences individuals have in both sweat rate and sweat electrolyte losses when doing the same task, at the same time, in the same environment, and wearing the same clothing.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

TABLE B-16 The Range of Losses for the Main Electrolytes Attributed to Sweat Rates Ranging from 4.8 L per Day to 9 L per Day

Electrolyte

Loss (mmol/day)a

Sodium

5–720

Chloride

5–540

Potassium

4–126

aSee Table B-15 for the range of normal sweat electrolyte concentrations.

BOX B-2
The Influence of Diet, Heat Acclimation, and Sweat Rate on Sodium and Potassium Concentrations in Sweat

SODIUM

  • ↑ dietary Na intake, ↑ sweat [Na]

  • heat acclimation, ↓ sweat [Na]

  • ↑ sweat rate, ↑ sweat [Na]

POTASSIUM

  • ↑ dietary K intake, ? sweat [K]

  • heat acclimation, ? sweat [K]

  • ↑ sweat rate, ? sweat [K]

SODIUM AND POSTEXERCISE REHYDRATION

In situations when large sweat losses occur over a relatively short time, effective recovery from dehydration will not occur when replacing water loss until the sodium loss is replaced as well. Solid food consumed along with the water will replace the sodium, but if food is not consumed, sodium salts should be added to the water (Maughan et al., 1996; Ray et al., 1998; Shirreffs and Maughan, 1998).

SODIUM–POTASSIUM INTERACTIONS

Sodium and potassium are complementary to each other in a number of ways and their consumption has particular effects on urinary excretion of the alternate cation, salt sensitivity, and blood pressure. However, in the studies referred to in the final sections below, the subjects were not stressed to a level that would add to significant sweat electrolyte losses in addition to the urinary losses described.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

TABLE B-17 Sweat (S) and Urinary (U) Loss of Potassium and Sodium

Condition

Intake and Loss

Reference

Potassium

24 hr exposed to heat stress

97 mmol (D); 60 mmol (S); 116 mmol (U+S)

Malhotra et al., 1976

6 hr intermittent walking

32 mmol (S); 23–70 mmol (U+S)

Armstrong et al., 1985a

Projected 24 hr losses

62–240 mmol (U+S)

Armstrong et al., 1985b

4 days with exercise

25 mmol verses 80 mmol (D); 31 mmol versus 67 mmol (U); 12 mmol versus 11 mmol (S)

Costill et al., 1982

Sodium

6 hr intermittent walking

72–244 mmol (U+S)

Armstrong et al., 1985a

Projected 24 hr losses

193–425 mmol (U+S)

Armstrong et al., 1985b

5 days heat acclimatization at 40 °C

348 vs. 174 vs. 66 mmol (D); 105 vs. 78 vs. 50 mmol (S); + 15 vs. + 29 vs. + 0.2 mmol (Balance)

Allsopp et al., 1998

5–9 L sweat per day

Sodium balance with 1.9–3.2 g (83–139 mmol)/day

Conn, 1949

NOTE: Where available, the dietary intake (D) of sodium or potassium is shown.

Dietary Intake and Sodium Excretion

With dietary sodium intakes of up to 3.2 g (140 mmol) per day, urinary potassium excretion generally remains lower than dietary potassium intake for at least 28 days (Sacks et al., 2001). However, with dietary sodium intakes greater that 6.9 g (300 mmol) per day, the urinary potassium excretion was greater than the dietary potassium intake over three days (Luft et al., 1982).

When potassium in the form of potassium bicarbonate or potassium chloride was supplemented in quantities greater than 4.7 g (120 mmol) per day, an increase in urinary sodium excretion was reported (van Buren et al., 1992). However, a potassium bicarbonate intake of either 2.7 or 4.7 g (70 to 120 mmol) per day was sufficient to reverse this increased loss when dietary sodium chloride intake was increased from 1.8 to 14.6 g (30 to 250 mmol) per day (Morris et al., 1999).

Salt Sensitivity

Salt sensitivity refers to the degree of blood pressure response to a change in dietary sodium intake. It is frequently classified by a dietary sodium chloride-induced increase in mean arterial blood pressure of 3 mm Hg or more. Studies have demonstrated that the expression of salt sensitivity is modulated by dietary

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

potassium intake, and this is one of the main rationales given for encouraging a high potassium intake. Morris and colleagues (1999) reported a 50 to 80 percent decrease of the identified salt-sensitive individuals who had a sodium chloride intake of 14.6 g (250 mmol) per day while they increased their potassium bicarbonate intake from 1.2 g (30 mmol) to 2.7 g (70 mmol) per day. It has been postulated that these effects on salt sensitivity occur with the natriuretic (high level of sodium loss in urine) effects of the potassium, increasing renal tubule excretion of sodium chloride, which seems to be unaffected by the anion accompanying potassium (IOM, 2004).

Blood Pressure

The modulating effects of dietary potassium intake on blood pressure appear to be related to the sodium/potassium ratio, and the effects increase with higher sodium chloride intake (Morris and Sebastian, 1995; Whelton et al., 1997). Reductions in systolic blood pressure of 2.5 mm Hg and in diastolic blood pressure of 1.5 mm Hg have been reported when 2 g (50 mmol) of urinary potassium was excreted, indicative of higher potassium intakes (Intersalt Cooperative Research Group, 1988).

CONCLUSIONS

For the most part, appropriate electrolyte intake for combat rations would be similar to that for daily intake in a healthy, balanced diet. Sodium requirements may be the main exception because of environmental influences. Because adaptations to significant changes in dietary intake of sodium take a number of days to fully develop, there are compelling reasons to have sodium in a short-term ration be present in a least the same quantities as those in the preceding daily diet.

The types of stresses experienced and their effects on sweat production may influence dietary electrolyte requirements. After a period of heavy sweating, sodium should be consumed, if possible, with any large volume of water to minimize diuresis. It is possible that sodium requirements may well differ with prolonged low sweat rates in comparison with the high sweat rates seen during periods of intense activity.

In keeping with the conclusions of the Panel on Dietary Reference Intakes for Electrolytes and Water, “data are presently insufficient to set different potassium intake recommendations according to the level of sodium intake, and vice versa. Likewise, data are insufficient to set requirements based on the sodium/potassium ratio” (IOM, 2004, p. 230).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

REFERENCES

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Allsopp AJ, Sutherland R, Wood P, Wootton SA. 1998. The effect of sodium balance on sweat sodium secretion and plasma aldosterone concentration. Eur J Appl Physiol 78(6):516–521.

Armstrong LW, Costill DL, Fink WJ, Bassett D, Hargreaves M, Nishibata I, King DS. 1985a. Effects of dietary sodium on body and muscle potassium content during heat acclimation. Eur J Appl Physiol 54(4):391–397.

Armstrong LE, Hubbard RW, Szlyk PC, Matthew WT, Sils IV. 1985b. Voluntary dehydration and electrolyte losses during prolonged exercise in the heat. Aviat Space Environ Med 56(8): 765–770.


Costill D. 1977. Sweating: Its composition and effects on body fluids. Ann N Y Acad Sci 301: 160–174.

Costill DL, Cote R, Fink WJ. 1982. Dietary potassium and heavy exercise: Effects on muscle water and electrolytes. Am J Clin Nutr 36(2):266–275.

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Intersalt Cooperative Research Group. 1988. Intersalt: An international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion. Br Med J 297(6644):319–328.

IOM (Institute of Medicine). 2004. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride and Sulfate. Washington, DC: The National Academies Press.


Kirkendall AM, Connor WE, Abboud F, Rastogi SP, Anderson TA, Fry M. 1976. The effect of dietary sodium chloride on blood pressure, body fluids, electrolytes, renal function, and serum lipids of normotensive man. J Lab Clin Med 87(3):411–434.


Leiper JB, Carnie A, Maughan RJ. 1996. Water turnover rates in sedentary and exercising middle aged men. Br J Sports Med 30(1):24–26.

Leiper JB, Pitsiladis Y, Maughan RJ. 2001. Comparison of water turnover rates in men undertaking prolonged cycling exercise and sedentary men. Int J Sports Med 22(3):181–185.

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Luft FC, Weinberger MH, Grim CE. 1982. Sodium sensitivity and resistance in normotensive humans. Am J Med 72(5):726–736.


Malhotra MS, Sridharan K, Venkataswamy Y. 1976. Potassium losses in sweat under heat stress. Aviat Space Environ Med 47(5):503–504.

Maughan RJ. 1991. Fluid and electrolyte loss and replacement in exercise. J Sports Sci 9 (Special):117–142.

Maughan RJ, Leiper JB, Shirreffs SM. 1996. Resortation of fluid balance after exercise-induced dehydration: Effects of food and fluid intake. Eur J Appl Physiol 73:317–325.

Morris RC, Sebastian A. 1995. Potassium-responsive hypertension. In: Laragh JH, Brenner BM, eds. Hypertension: Pathophysiology, Diagnosis, and Management. 2nd ed. New York: Raven Press. Pp. 2715–2726.

Morris RC Jr, Schmidlin O, Tanaka M, Forman A, Frassetto L, Sebastian A. 1999. Differing effects of supplemental KCl and KHCO3: Pathophysiological and clinical implications. Semin Nephrol 19(5):487–493.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Overlack A, Ruppert M, Kolloch R, Kraft K, Stumpe KO. 1995. Age is a major determinant of the divergent blood pressure responses to varying salt intake in essential hypertension. Am J Hypertens 8(8):829–836.


Pitts RF. 1959. The Physiological Basis of Diuretic Therapy. Springfield, IL: C.C. Thomas.


Ray ML, Bryan MW, Ruden TM, Baier SM, Sharp RL, King DS. 1998. Effect of sodium in a rehydration beverage when consumed as a fluid or meal. J Appl Physiol 85(4):1329–1336.


Sacks FM, Svetkey LP, Vollmer WM, Appel LJ, Bray GA, Harsha D, Obarzanek E, Conlin PR, Miller ER 3rd, Simons-Morton DG, Karanja N, Lin PH. 2001. Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. DASH-Sodium Collaborative Research Group. N Engl J Med 344(1):3–10.

Sawka M, Pandolf K. 1990. Effects of body water loss on physiological function and exercise performance. In: Gisolfi C, Lamb D, eds. Perspectives In Exercise Science and Sports Medicine. Vol. 3. Fluid homeostasis during exercise. Carmel, IN: Benchmark Press Inc. Pp. 1–38.

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Shirreffs SM, Maughan RJ. 1998. Volume repletion after exercise-induced volume depletion in humans: Replacement of water and sodium losses. Am J Physiol 274(5 Pt 2):F868–F875.

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Whelton PK, He J, Cutler JA, Brancati FL, Appel LJ, Follmann D, Klag MJ. 1997. Effects of oral potassium on blood pressure. Meta-analysis of randomized controlled clinical trials. J Am Med Assoc 277(20):1624–1632.


Zhou BF, Stamler J, Dennis B, Moag-Stahlberg A, Okuda N, Robertson C, Zhao L, Chan Q, Elliott P. 2003. Nutrient intakes of middle-aged men and women in China, Japan, United Kingdom, and United States in the late 1990s: The INTERMAP study. J Hum Hypertens 17(9):623–630.

Other Bioactive Food Components and Dietary Supplements

Rebecca B. Costello and George P. Chrousos, National Institutes of Health

INTRODUCTION

Evaluation of the potential beneficial effects of nutrition supplements or bioactive food components should consider an individual’s baseline status and the many different stress states in response to discrete types of stressors. Also, we need to distinguish between acute, subacute, and chronic stressors and the type, amount, and duration of demands that each imposes on the individual. Another issue is the constitution of the individual, dictated by genetics, developmental intrauterine and early life history, and late postnatal and current environment.

Psychosocial or physical stressors or a combination of the two produce different kinds of adaptive responses and have different types of material requirements depending on both the size and duration of the stressor. During stress, be it psychosocial or physical, all four major neurotransmitter systems—noradrenergic, serotonergic, cholinergic, and γ-aminobutyric acid (GABA)ergic—are activated. This poses increased needs for precursor amino acid molecules as well as for the

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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energy necessary for their synthesis, secretion, and electrochemical effects. Also, there is increased demand for the necessary coenzymes, some of which are essential vitamins that must be taken from the environment. When physical stress is present, one has to consider both the increased needs for the stress neurotransmitter synthesis, secretion, and effects, and the peripheral energy demands, the latter becoming of major importance. In this instance, the availability of nutrients and oxygen and the presence of healthy energy-producing machinery, including adequate numbers of healthy mitochondria and the ability to switch from aerobic to anaerobic metabolism, are crucial components of a successful adaptation.

This chapter reviews a number of bioactive food components and dietary supplements that have been tested or suggested for their performance-enhancing effects. Among these are the well-characterized and extensively studied amino acids tyrosine and tryptophan for their role in modulating neurotransmitter concentrations. Also reviewed are L-carnitine and coenzyme Q10 for their role in supporting mitochondrial energy metabolism, as well as several botanical ingredients, Eleutherococcus senticosus (Siberian ginseng), Cordyceps sinensis, and Rhodiola, for their adaptogenic qualities, and Ginkgo biloba for cognitive function and mitigation of acute mountain sickness.

NEUROTRANSMITTER PRECURSORS

Tyrosine and tryptophan, two of the large neutral amino acids (LNAA), when given in single, nonphysiologic doses or within special diets, have been shown to alter brain activity. Tyrosine is the precursor for the neurotransmitters dopamine, norepinephrine, and epinephrine. The working hypothesis is that tyrosine can mitigate the adverse effects of acute stress by modulating levels of norepinephrine. Tryptophan is the precursor for the neurotransmitter serotonin. Its role in regulating mood (particularly depression) and alertness but also pain sensitivity, aggression and food consumption may, under certain circumstances, support various aspects of performance. This topic has been well described in previous IOM reports (IOM, 1994, 1999) and in reviews by Lieberman (1994, 1999, 2003) and thus this chapter will concentrate on more recent research findings dealing with the roles of tyrosine and tryptophan in modulating performance.

TYROSINE

Animal studies have demonstrated that performance decline observed in highly stressed animals can be restored by supplementation with tyrosine (IOM, 1994). This has recently been confirmed (Yeghiayan et al., 2001); rats pretreated with L-tyrosine (200 to 400 mg/kg body weight) in a dose-dependent fashion improved performance in a forced-swim test following acute cold stress. Tyrosine also improved mood and performance concomitant with increases in hippocampal norepinephrine concentrations following cold exposure.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

Human studies involved in supplementing with L-tyrosine have shown that the adverse effects of hypoxia and cold, lower body negative-pressure stress, and psychological stress can be reduced by tyrosine supplementation in dose ranges of 85 to 100 mg/kg body weight (IOM, 1994). Work by Neri and colleagues (1995) in a clinical study of a small number of US Marine research subjects, demonstrated that 75 mg/kg of L-tyrosine, compared to the results of a cornstarch control given in banana-flavored yogurt on two occasions to the soldiers after one night’s sleep loss, ameliorated the usual performance decline on a set of psychomotor tasks over a 13-hour test session. A significant reduction in lapse probability on a high-event rate vigilance task was also demonstrated with improvements lasting approximately three hours. When two grams of L-tyrosine was administered in the form of a protein-rich drink for a period of five days, military cadets performed better on enhanced memory and tracking tests compared with those who ingested an isocaloric placebo drink (Deijen et al., 1999). Most recently in a study designed to test whether repeated ingestions of tyrosine during prolonged exercise would improve physical performance in competitive cyclists, Chinevere and colleagues (2002) administered L-tyrosine alone (25 mg/kg), tyrosine with a carbohydrate supplement, or a placebo in a double-blind controlled study and found a lack of effect on physical endurance parameters of oxygen uptake, heart rate, rate of perceived exertion (RPE) at any time during the 90-minute cycling session. Although an increase in the plasma to free-tyrosine:tryptophan ratio (a more sensitive marker of amino acid transport across the blood-brain barrier than plasma levels alone) was noted for those who consumed the tyrosine-containing supplements, it did not translate into an increase in performance. Thus, it appears that the benefits of tyrosine supplementation continue to be accrued for enhancements in cognitive function but not for physical performance.

L-Tyrosine is generally recognized as safe (GRAS) status in the United States. It is safe in doses up to 150 mg/kg/day for two weeks (IOM, 2002), although a number of issues remain to be addressed concerning routine supplementation with tyrosine. Yet to be demonstrated is tyrosine’s effects across a wider range of stressors. There is a need to establish a dose-response function for tyrosine in humans and to estimate an upper level of intake. Documentation in human studies is still lacking regarding its efficacy in situations of chronic stress. The most effective method of supplementation for the soldiers (foods versus supplements) has yet to be determined.

TRYPTOPHAN

Tryptophan has been shown to have sedative-like effects on humans when administered in pure form and in sufficient quantity (IOM, 1994; Lieberman et al., 1986). It may also be useful as a mild sleep aid in military operations as it does not appear to impair some aspects of performance (IOM, 1994; Lieberman

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

et al., 1986). Research on supplementation with L-tryptophan was halted in 1990 when products were removed from the market due to an outbreak of a rare condition called eosinophilia-myalgia syndrome (EMS). The exact etiology of this outbreak remains undefined. L-Tryptophan however is available in the United States in special dietary products for limited use under medical supervision, such as infant formulas. Consumption of increased levels of L-tryptophan when “balanced” with other amino acids in foods or as a fortificant has not been associated with EMS.

Dietary carbohydrates produce major, insulin-mediated decreases in the availability of LNAA, with lesser reductions in plasma tryptophan, which in effect raises the plasma tryptophan:LNAA ratio, facilitating tryptophan’s entry into the brain. In contrast, intake of dietary protein has been shown to lower this ratio as they contribute less tryptophan to the circulation than do other LNAAs. Strüder and Weicker (2001) reviewed more than 20 human studies and concluded that nutritional manipulation of serotonin in the brain has variable effects on reducing fatigue and enhancing performance outcomes. This physiologic response has been recently reexamined by Wurtman et al. (2003) evaluating a high-carbohydrate versus a high-protein breakfast meal, as typically eaten by Americans, on the plasma tryptophan:LNAA ratio. It was found that the carbohydrate-rich and protein-rich breakfasts had significantly different effects on the plasma tryptophan:LNAA ratio (54 percent median difference) and tyrosine:LNAA ratio (28 percent median difference). In evaluating carbohydrate-rich and protein-poor diets in stress-prone individuals, Markus et al. (1998, 1999), have demonstrated that a carbohydrate-rich/protein-poor diet compared with a protein-rich/carbohydrate-poor diet increased the ratio of tryptophan:LNAA in the plasma and improved stress coping during high, uncontrollable laboratory stress in the high stress subjects only; thus suggesting a higher requirement for tryptophan and enhanced serotonergic functioning in the high-stress compared with low-stress subjects.

Following on these findings and further manipulating dietary constituents, Markus and colleagues (2000; 2002) designed clinical studies to evaluate mood and cognitive performance in high-stress-vulnerable subjects by using an enriched whey protein supplement high in tryptophan content (6 percent from α-lactalbumin) in a double-blind, placebo crossover study. Tryptophan 12.32 g/kg (in the form of α-lactabumin), when given in a chocolate beverage drink versus a sodium caseinate control beverage containing 9.51 g/kg of tryptophan twice daily, increased the plasma ratio of tryptophan:LNAA, enhanced plasma prolactin levels (a measure of enhanced brain serotonin function), and decreased cortisol levels (a measure of the reactivity of the stress response system) with improvements in cognitive performance in high-stress-vulnerable subjects only, as compared with low-stress subjects. Additional work in this area has been performed by Beulens and colleagues (2004) in healthy male subjects randomized to either an α-lactalbumin supplement plus carbohydrate or carbohydrate supplement only consumed after

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

a breakfast consisting of 19 percent protein. Measurements were obtained at baseline, 30 minutes, and 90 minutes postingestion. The team demonstrated moderately increased levels (16 percent) of the plasma tryptophan:LNAA ratio with the α-lactalbumin supplement with no effect on appetite, food intake, macronutrient preference, or mood as compared with the carbohydrate-only supplemented group.

What is yet to be determined from these studies is the threshold level of tryptophan necessary in a protein-rich/carbohydrate-poor diet that will elicit the maximum response on the plasma tryptophan:LNAA ratio and subsequent levels of serotonin in the brain needed to effect changes in cognitive performance. A study by Teff and colleagues (1989) suggests that only an increase in tryptophan:LNAA ratio of 50 percent or more causes meaningful increases in brain serotonin; however, animal studies have shown effects at lower levels. What can be ascertained at present from this work is the relative safety of use from naturally occurring, enriched levels of tryptophan in food-based products. Improvements in cognitive function were evident together with immediate and short-term effects on plasma ratios of amino acids. Table B-18 summarizes the details of these studies.

METABOLIC COFACTORS

Carnitine

Carnitine is a conditionally essential nutrient because, under certain conditions, its requirements may exceed the body’s capacity to synthesize it. Orally, L-carnitine is used for treating primary carnitine deficiency, secondary carnitine deficiency due to inborn errors of metabolism, and carnitine deficiency in people requiring hemodialysis. Aside from primary or secondary deficiency states, typical intake of carnitine from foods provides 50 to 100 mg/day in the United States. No evidence suggests a greater amount is needed to support normal metabolic functions. The role of carnitine is to chaperone the transport of medium- to long-chain fatty acids across mitochondrial membranes to facilitate their oxidation with subsequent energy production. By formation of acylcarnitines from acyl-CoA metabolic intermediates, carnitine may optimize the intracellular milieu for complete oxidation of glucose and fatty acids. Carnitine also has an important metabolic role in the exercising muscle. The hypothesis is that supplementation might enhance the oxidation of fatty acids during exercise, sparing the use of muscle glycogen, thereby delaying the onset of fatigue and culminating in enhanced physical performance. The data in this area are mixed and are not robust. For a number of reasons, carnitine supplementation would not be expected to enhance physical performance: whole-body carnitine homeostasis is highly regulated and compartmentalized; it exists in a large endogenous pool refractive to rapid change; exhibits low bioavailability (16 to 18 percent), with a rapid renal excretion; and it is regulated by a number of saturable transport

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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TABLE B-18 Results of Human Studies Utilizing Whole Foods on Tryptophan:LNAA Ratio

Reference

Subjects

Study Design

Preparation

Beulens et al., 2004

N = 18 healthy males, mean age 22 ± 4 y

DBRPC-CO

CHO only (10 g CHO, 0 protein)

versus

α-lactalbumin plus CHO

(CHO 20 g, protein 12 g as α-lactalbumin enriched whey protein)

Markus et al., 1998

N = 48 healthy men and women; mean age 21.2 ± 0.4 years 24 high stress prone; 24 low stress prone

Open

CR/PP (62% CHO, 3.6% protein)

versus

PR/CP (26.3% CHO, 40.4% protein)

Markus et al., 1999

N= 43 healthy men and women; mean age 22.5 years 22 high stress prone and 21 low stress prone

Open

Same as above

Markus et al., 2000

N = 58

DBPC healthy mean and women; mean age 20.5 years. 29 high stress prone and 21 low stress prone

α-lactalbumin enriched whey protein

(12.32 g/kg tryptophan; ratio tryptophan:LNAA 8.7)

versus

Sodium caseinate control

(9.51 g/kg tryptophan; ratio tryptophan:LNAA 4.7)

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

Dosing Schedule

Test Exposure

Effects

Drink supplement—one hour after breakfast containing CHO 50%, protein 15% and fat 35%.

2 test sessions, each separated by 2 weeks. Assessment of plasma amino acids, serum prolactin, insulin concentrations and mood (POMS) at baseline, 60 and 90 minutes.

Mean tryptophan:

LNAA ratio increased (16%) from 0.084 ± 0.003 on α-lactalbumin diet to 0.097 ± 0.003 and decreased 17% from 0.087 ± 0.003 to 0.073 ± 0.002 after CHO only diet.

Decrease in serum prolactin slightly smaller after α-lactalbumin than CHO alone.

No significant differences in appetite, food intake, macronutrient preference, insulin levels or mood between diets.

After α-lactalbumin, changes in tryptophan:LNAA ratio correlated significantly with changes in anger score (r=-0.65), and tension score (r=0.59).

Consumed as breakfast, snack and lunch; diet test periods were 4 weeks apart.

Mental arithmetic and memory scanning test during uncontrollable stress (POMS).

Mean tryptophan:LNAA ratio increased from 0.074 ± 0.01 on PR/CP to 0.105 ± 0.015 on CR/PP (42% increase).

High stress subjects on CR/PP did not show stress-induced rise in depression (POMS).

Mean reaction time was not significantly different between high stress and low stress subjects and increased for both groups on CR/PP diet.

Same as above

Mental arithmetic and memory scanning test and mood assessment (POMS) during controllable and uncontrollable stress.

Memory scanning after controllable stress improved in high stress subjects on CR/PP diet.

Mean reaction time for high stress on PR/CP increased significantly after controllable stress from 700 to 900 minutes.

Active ingredients given in matching chocolate drink given before breakfast and before lunch. Diets were isoenergetic with equal amounts of CHO, fats, and protein.

Stress-inducing timed mental arithmetic task with industrial noise stress, and POMS. Salivary and plasma cortisol levels. Skin conductance. Heart rate.

Mean tryptophan:LNAA ratio increased from 0.071 ± 0.012 on casein diet to 0.104 ± 0.013 on α-lactalbumin diet (48%).

High stress subjects had higher (40%) prolactin concentrations, decreased salivary and plasma cortisol levels and reduced depressive (POMS) feelings under stress on α-lactalbumin.

Rise in the cortisol stress response was prevented in high stress but not in low stress on α-lactalbumin diet.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

Reference

Subjects

Study Design

Preparation

Markus et al., 2002

N = 52 healthy men and women 23 high stress prone and 29 low stress prone

DBPC

Same as above

Wurtman et al., 2003

N = 9 healthy, normal weight men women, mean age 24.2 ± 1.3 years

RC

CR (69.9 g CHO, 5.2 g protein)

versus

PR (15.4 g CHO, 46.8 g protein)

NOTE: CHO = carbohydrate; CP = carbohydrate poor; CR = carbohydrate rich; CR/PP = carbohydrate rich/protein poor; DBPC = double-bind placebo controlled; DBRPC-CO = double-blind randomized placebo controlled crossover; LNAA = large neutral amino acids; POMS = Profile of Mood States; PP = protein poor; PR = protein rich; PR/CP = protein rich/carbohydrate poor; RC = randomized control.

mechanisms. Studies suggest that muscle function is sensitive to carnitine supplementation when muscle carnitine content is < 25 to 50 percent of normal but insensitive to changes in muscle carnitine content around normal levels (Brass, 2004). Exercise studies in healthy subjects have failed to consistently define an effect of supplementation on more than one metabolic parameter of interest. Many of the studies suffer from small sample sizes, lack of appropriate control groups, and short duration. In general, L-carnitine appears to be well tolerated, and no serious toxicity has been demonstrated when given in oral doses up to several grams (Goa and Brogden, 1987). The D-isomer is not biologically active and D-isomer formulations can compete with the L-isomer. At this time, it appears that L-carnitine does not have a significant role in enhancing physical performance in the short term, but additional research is needed to ascertain the benefits of L-carnitine in certain states that alter the requirements for L-carnitine, such as physical or psychological stress. These studies would benefit from well-designed, adequately powered clinical trials with robust clinical performance endpoints.

Also of interest is L-carnitine’s emerging role in immunomodulation, as

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

Dosing Schedule

Test Exposure

Effects

Same as above

Computerized stress-inducing timed mental task

Mean tryptophan: LNAA ratio increased from 0.073 ± 0.012 on casein diet to 0.104 ± 0.013 on α-lactalbumin diet (43%).

Mean reaction time for high stress on α-lactalbumin was significantly lower (758 ± 137 ms) compared to casein control (800 ± 173 minutes).

2 breakfasts, 3–7 days apart

Timed collection of plasma for assessment of tryptophan:LNAA ratio at baseline, 40, 80, 120, and 240 min

Tryptophan:LNAA and tyrosine/LNAA ratios on CR diet at 40, 80, 120, 240 were not different from baseline.

Tryptophan:LNAA and tyrosine/LNAA ratios on PR diet at 40, 80, 120, 240 minutes were statistically significant from baseline.

Median difference for tryptophan:LNAA was 54% (range 36–88%) and for tyrosine:LNAA was 28 % (range 10–64%).

demonstrated in both animal and human studies. In rodent studies, carnitine (50 to 100 mg/kg body weight) was shown to reduce lipopolysaccharide (LPS)-induced cytokine production with improved survival during cachexia and septic shock (Ruggiero et al., 1993; Winter et al., 1995). Carnitine was also shown to reduce the ex vivo release of tumor necrosis factor alpha (TNF-α) by S. aureus-stimulated human polymorphonuclear white blood cells (Fattorossi et al., 1993). Carnitine administration in patients undergoing surgery (8 g intravenously) or in patients with HIV+ (6 g/day for two weeks) can significantly decrease serum TNF-α levels (De Simone et al., 1993; Delogu et al., 1993). Recently, Alesci and colleagues (2004) have suggested that the immunomodulatory properties of L-carnitine may be mediated by its interaction with the glucocorticoid receptor. Similar to dexamethasone, which is a synthetic glucocorticoid, carnitine at millimolar concentrations triggered nuclear translocation of human glucocorticoid-receptor alpha (GRα), stimulated GRα-mediated transactivation of known glucocorticoid-responsive promoters, suppressed in a GRα-dependent fashion; and stimulated release of proinflammatory cytokines from human monocytes. These proposed modulatory actions of L-carnitine on the glucocorticoid receptor

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

may be of interest to the military as related to the stressful training undertaken by soldiers in the Army Ranger program. As noted previously by Kramer et al. (1997) and Martinez-Lopez et al. (1993), infection rates in Rangers were notably elevated in association with derangements in indices of immune function. High levels of glucocorticoids during chronic stress suppress most aspects of the immune response (Dhabhar and McEwen, 1997) and the ability to fight infection and mount an antibody response (Dhabhar, 2002). The net effect is a suppression of proinflammatory cytokines by glucocorticoids, with an increase in antiinflammatory cytokines leading to overall immunosuppression (IOM, 2004). New mechanistic data on L-carnitine may warrant research studies in situations of high stress and compromised nutritional status.

Coenzyme Q10

Coenzyme Q10 (CoQ10) is a member of the family of compounds known as ubiquinones. All animals, including humans, can synthesize ubiquinones, and no CoQ10 deficiency syndromes have been reported in humans; therefore, a varied diet provides sufficient CoQ10 for healthy individuals. Oral supplementation with CoQ10 increases the plasma and lipoprotein concentrations of CoQ10 in humans (Crane, 2001; Mohr et al., 1992). What is not clear is whether supplementation increases CoQ10 concentrations in other tissues of individuals with normal endogenous CoQ10 synthesis. Several placebo-controlled clinical trials in either trained or untrained men have demonstrated a lack of effect of CoQ10 on parameters of physical performance. These parameters include VO2max and exercise time to exhaustion (Braun et al., 1991; Malm et al., 1997; Porter et al., 1995; Weston et al., 1997), blood lactate levels, and rate of perceived exertion (Porter et al., 1995) in response to cycle ergometer testing. Doses ranging from 100 to 150 mg of CoQ10, with intervention periods lasting from three to eight weeks in duration, have been reported. Two studies in trained men found significantly greater improvements in measures of anaerobic (Malm et al., 1997) and aerobic exercise performance (Laaksonen et al., 1995) with a placebo as compared with CoQ10. While supplementation with CoQ10 appears safe in doses as high as 1,200 mg/day up to 16 months (Shults et al., 2002) its role for enhancing performance cannot be supported with existing data.

PERFORMANCE-ENHANCING BOTANICALS

Panax ginseng

Among the botanicals considered as adaptogens, agents taken as a general tonic to increase resistance to environmental stress, Panax ginseng (Asian ginseng) is the most studied in terms of enhancing performance. Its ergogenic effects have been characterized in terms of physical performance (exercise out-

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

comes, physiological changes, metabolic measures, and assessment of hormone levels) as well as in terms of cognitive performance (psychomotor measures, reaction time, mood, cognition, memory, and accuracy of repetitive tests) [see review by Bucci et al. (2004)]. Conclusions drawn from a recent systematic review of the literature note that the evidence is contradictory for benefits to physical performance but may be suggestive of benefit for psychomotor performance and cognitive behavior (Vogler et al., 1999). The majority of the studies found at least one significant change in mental functions with Asian ginseng, but responses were not uniform across studies. While the use of ginseng is associated with a feeling of general well-being, in addition, reaction times to auditory or visual cues improved and fatigue and errors in cognitive tasks reduced. Short-term use (four weeks or less) of ginseng does not result in benefits to mental or physical performance, but long-term use (over 12 weeks) in situations of compromised performance suggests some benefit in mood, reaction times, neuromuscular control, mental functions, and work capacity (Bucci et al., 2004). As with other clinical studies evaluating dietary supplements, ginseng studies also suffer from small sample sizes, short duration of use, and poorly characterized products. Also, it appears that ginseng with its delayed onset of action would not be an appropriate supplement for military use in acute situations.

Ginkgo biloba

Ginkgo biloba extract is one of the most prescribed phytomedicines in Germany and France. Physicians prescribe it for dementia, vertigo, anxiety, headaches, tinnitus, peripheral vascular occlusive disease, and other problems. There are also indications that it is an effective antioxidant with free-radical scavenging activity (Christen, 2004). In recent years, ginkgo has been a top selling dietary supplement in the United States. Ginkgo preparations are derived from the dried, green leaf of Ginkgo biloba. L. Ginkgo biloba extracts (GBEs), contain several constituents including flavonoids, terpenoids, and organic acids. GBE is standardized to contain 24 percent flavonoids and 6 percent terpenes. Although many of ginkgo’s individual constituents have intrinsic pharmacological effects, there is some evidence that the constituents work synergistically to produce more potent pharmacological effects than any individual constituent.

Evidence suggests that chronic administration of standardized extracts of Ginkgo biloba can ameliorate cognitive decline associated with aging (Ernst and Pittler, 1999; Oken et al., 1998). However, relatively few studies of ginkgo’s effect on cognitive measures in healthy adults are available. A systematic review (Canter and Ernst, 2002) identified nine placebo-controlled, double-blind studies utilizing standardized extracts of Ginkgo biloba, the longest trial lasting 30 days. The authors concluded that there were no consistent positive effects of ginkgo on objective measures of cognitive function in healthy populations. Two studies published since the 2002 review provide additional data suggesting beneficial

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

effects for ginkgo on measures of cognitive function. Kennedy and colleagues (2002), building on a series of previous investigations (Kennedy et al., 2000, 2001), evaluated the acute cognitive effects of herbal extracts. They conducted a randomized placebo-controlled double-blind crossover study to compare the effects of single doses of GBE, ginseng, and a combination product on aspects of mood (Bond-Lader visual analogue scale) and cognitive performance (Cognitive Drug Research computerized assessment battery, CDR) and several subtraction mental arithmetic tasks (Kennedy et al., 2002). Fifteen female and five male healthy young subjects (mean age 21.2) received 360 mg of GBE (GK501), 400 mg of ginseng (G115), 960 mg of a product combining the two extracts (Ginkoba M/E), and a matching placebo on four separate occasions. Each test session was separated by a seven-day washout period. Measurements were obtained at baseline 1, 2.5, 4, and 6 h after dosing. All three treatments were associated with improved secondary memory performance defined as accuracy of immediate and delayed word recall, picture, and word recognition tasks on the CDR battery. Ginseng showed some improvement in the speed of performing memory tasks (speed of performance of spatial and numeric working memory and picture and word recognition tasks) at four hours postdose. Additionally, ginseng showed improvements in the accuracy of attentional tasks (accuracy of performing choice reaction time and digit vigilance tasks) at 2.5 h postdose. GBE and the GBE/ginseng combination improved performance on both the serial threes and serial sevens subtraction tests at six hours postdose. In another study conducted in 60 healthy adults aged 50 to 65 years, Cieza and colleagues (2003) demonstrated positive effects of 240 mg of GBE (EGb761) three times daily over a four-week period. Primary outcome measures included the subject’s judgment of their own mental health, their general health and their quality of life determined on the basis of three difference visual analog scales. Secondary outcomes (15 tests and procedures) were chosen to represent neurobiologically based functions. Results of finger tapping test-maximal tempo indicated favorable effects of GBE on mental function action and reaction times.

Perhaps of greater interest in the military theater, GBE has also been studied for the prevention and mitigation of acute mountain sickness or high-altitude illness. The Lake Louise Consensus Group defined acute mountain sickness (AMS) as the presence of headache in an unacclimatized person who has recently arrived at an altitude above 2,500 meters plus the presence of other symptoms such as: gastrointestinal symptoms (anorexia, nausea, or vomiting), insomnia, dizziness, and lassitude or fatigue (Roach et al., 1993). If left untreated the condition may progress to life threatening pulmonary or cerebral edema. Whether or not AMS occurs is determined by the rate of ascent, the altitude reached, the altitude at which an affected person sleeps, and individual physiology. Physical fitness does not appear to be protective against AMS (Hackett and Roach, 2001). Safe and effective drugs, such as acetazolamide, are available to treat AMS.

Four randomized double-blind placebo-controlled studies (Chow et al., 2002;

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

Gertsch et al., 2002, 2004; Roncin et al., 1996) and one nonrandomized but double-blind placebo-controlled study (Leadbetter et al., 2001) totaling 781 participants have been reported utilizing GBE for AMS with mixed results. The dosage of GBE ranged from 160 to 240 mg (brands not always identified) daily with pretreatment ranging from one to thirty days prior to ascent. In the studies by Chow et al. (2002) and Gertsch et al. (2004) the comparator drug was acetazolamide, given as 250 mg twice daily, which demonstrated superiority in prevention of acute symptoms as coded using the Lake Louise Scoring system and showed that ginkgo offered no additional benefit in reduction of symptoms compared to placebo. While the study by Gertsch et al. (2004) enrolled 614 healthy western trekkers, mean age 36.6 years old, and predominately male, a number of shortcomings of the study were identified. These included short duration of dosing prior to ascent (3 to 4 doses), administration of the intervention to participants at a high baseline altitude (as opposed to starting the intervention at sea level before ascent), coupled with a 20 percent drop-out rate (although analysis was by intention-to-treat). In the study by Chow et al. (2002), both men and women were enrolled (age range 25 to 65, mean 36.5 years) and were dosed five days prior to ascent, and were driven from a level of 4,000 feet to a final altitude of 12,470 feet over a two-hour period. An earlier study by Gertsch and colleagues (2002) demonstrated that pretreatment of 180 mg of GBE (GK501) one day prior to ascent from sea level to 4,205 meters over three hours by air showed that ginkgo lowered the incidence of AMS but not significantly as compared to placebo. The two studies with positive outcomes for GBE (Leadbetter et al., 2001; Roncin et al., 1996) provided either 160 or 240 mg of GBE daily with pretreatment ranging from 5 to 30 days prior to ascent. The study by Roncin and colleagues (1996) tested EGb761 for the prevention of AMS and also studied vasomotor changes (cold gradient) of the extremities using plethysmorgraphy during a 30-day Himalayan expedition. These investigators found that none of the subjects randomized to EGb761 developed acute mountain sickness versus 40.9 percent of subjects in the placebo group as determined by responses to an Environmental Symptoms Questionnaire (ESQ)–cerebral factor (Sampson et al., 1983). A small percentage (13.6 percent) of subjects on EGb761 compared with subjects on placebo (81.8 percent) developed AMS as determined by the ESQ–respiratory factor. Evaluation of a “cold gradient” was measured by plethysmography and a specific questionnaire. Subjects randomized to EGb 761 showed a mean improvement of the cold gradient of 22.8 percent compared to the placebo group that deteriorated by 104 percent across 20 days of study. There was a marked increase in hand blood flow in the subjects on ginkgo compared to placebo. Also of possible importance to field maneuvers, diuresis of the EGb 761 group was decreased to a much lesser extent than in the placebo group suggesting a tendency for poorly adapted subjects to accumulate excess fluid, which could predispose them to an increased risk of developing altitude edema. The mechanism of action for the effects of GBE cannot be attributed to a single

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

action or to a single molecule in the extract. Research suggests that ginkgo could act in several different ways to prevent AMS. It may block the enzyme inducible nitric oxide synthase, which produces nitric oxide, act as an antioxidant oxygen radical scavenger, or may block platelet-activating factors (Christen, 2004).

In the studies reviewed above, ginkgo was well tolerated and without side effects and is likely safe when used orally and appropriately. Ginkgo may be contraindicated in individuals with epilepsy or in individuals who are prone to seizures, individuals with diabetes or those taking prescription anticoagulants.

New data on GBE for the prevention of AMS from controlled trials coupled with data from basic and mechanistic studies provides justification for additional investigation of this product. Lastly, if GBE were to be incorporated into food-based products and depending on the intended use of the product, potential regulatory issues (unlike vitamin and mineral nutrients) would need to be addressed prior to distribution.

OTHER ADAPTOGENIC HERBS

Preliminary data exist for a number of other adaptogenic herbs to include Cordyceps sinensis, Eleutherococcus senticosus, and Rhodiola. Cordyceps sinensis gained the interest of Americans in 1994 following the unprecedented record-breaking running performances by Chinese athletes (Steinkraus and Whitfield, 1994). In China, Cordyceps sinensis is an herbal pharmaceutical under investigation for treatment of immune deficiencies, cardiovascular diseases, diabetes, cancer, and inflammatory diseases (Zhu et al., 1998a, b). Five small, controlled, human studies measuring parameters of physical performance (such as VO2max, ventilatory threshold, respiratory exchange ratio, anaerobic threshold, and exercise time) using the same Cordyceps sinensis product (3 g/day) for 4 to 12 weeks suggest that Cordyceps sinensis may be associated with some improvements in untrained persons, but these improvements could not be routinely expected for trained persons (Bucci et al., 2004).

Rhodiola species, also known as goldenroot, roseroot, and Arctic ginseng, have been well studied and characterized by Russian and Scandinavian researchers. The Soviet Ministry of Health has approved a Rhodiola extract liquid (in 40 percent ethanol) for use as a stimulant to relieve fatigue, improve memory, improve attention span and work productivity in healthy persons (Brown et al., 2002; Germano et al., 1999; Kelly, 2001). Sweden and Denmark also have approved Rhodiola extracts (SHR-5) as antifatigue stimulants and adaptogens (Brown et al., 2002; Shevtsov et al., 2003). In one randomized double-blind placebo controlled trial in 121 military cadets on night duty, 185 mg of Rhodiola rosea SHR-5 extract acutely improved an antifatigue index for mental work while fatigued, and it decreased errors on ring attention and numbers tests (Shevtsov et al., 2003). In summary, standardized extracts used in clinical trials show potential for improving some aspects of mental (electroencephalogram, memory, reduction of errors performing

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

tasks, shooting accuracy, and hearing) and physical (increased work, increased run time to exhaustion, heart rate record post-exercise, and less fatigue) performance in athletes and sedentary subjects (Bucci et al., 2004). A combination formula containing 1,000 mg of Cordyceps sinensis and 300 mg of Rhodiola was recently tested with a two week treatment in 17 competitive amateur cyclists in a randomized, placebo-controlled, double-blind study design. The formula failed to elicit positive changes for peak exercise variables (VO2max, time to exhaustion, peak workload, or peak heart rate) as well as for subpeak exercise variables (power output ventilatory threshold, respiratory compensation or VO2) (Earnest et al., 2004). The authors note that a longer period of supplementation may have provided a more efficacious response, but this awaits further study.

SUMMARY

This chapter has focused on a number of bioactive food and dietary supplement components that have been evaluated for their performance enhancing qualities. The data presented suggest that if amino acid precursors are to be further tested, their incorporation into a food matrix is preferable over that of a dietary supplement. While research on L-carnitine for enhancing physical performance has not been promising, the role for L-carnitine and its interactions with the glucocorticoid receptor, and particularly for its potential effects on immunomodulation, warrant further exploration. The use of botanicals most likely would not provide short-term or immediate enhancement to performance, except possibly for standardized extracts of Rhodiola and Ginkgo biloba, which warrant more rigorous study.

In the design of future studies, important considerations are the increased precursor, coenzyme, and energy demands during stress that would be met differently by the human population, possibly distributed in the form of a bell-shaped curve, with individuals ranging from coping poorly to coping extremely well. Individuals to benefit the most from necessary supplements would most likely be in the “coping poorly” category, as was shown in the studies by Markus et al. (1998, 1999, 2000). Of course, persons with discrete defects in stress coping, constituting a separate group of individuals with their own transposed bell-shaped curve, could also benefit from needed supplements if their defects could be corrected in the presence of excess bioactive food components. The possibility that only a subgroup of the population would benefit from bioactive food components, and only when they are challenged by stress, makes the design of clinical studies of these agents difficult, because it presupposes controlling two continuous variables—degree of coping capacity and amount of stress impose—both of which depend on myriad factors. The former is a product of genetics, developmental history, and environment, while the latter depends on the diverse types of stressors applied with different strengths for different times.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Effect of Physical Activity and Other Stressors on Appetite: Overcoming Underconsumption of Military Operational Rations, Revisited

R. James Stubbs and Stephen Whybrow, Rowett Research Institute

Neil King and John E. Blundell, Leeds University

Marinos Elia, Southhampton General Hospital

INTRODUCTION

The ready availability of a huge variety of energy-dense, palatable food is considered partly responsible for the current trends in obesity and attendant diseases in Western society. Although intuitively, it would seem that widescale under-consumption should not be a problem, underconsumption of military operational rations has been a subject of some concern to the United States. In 1995, the Committee on Military Nutrition Research (CMNR) produced a report entitled Not Eating Enough (IOM, 1995), a comprehensive report covering the causes and consequences of underconsumption in field operations, the strategies, and need for research to increase intake of military rations in combat (IOM, 1995). The majority of data sourced for this report is related to experimental, comprehensive field studies during military exercises and with garrisoned soldiers. These environments clearly differ from each other and from combat itself. The report acknowledged a lack of data from combat or near-combat situations regarding ration intake, acceptability, appetite and feeding behavior. Understandably, most data are anecdotal; however, the report noted that the nagging hunger of energy restriction differs from the appetite-suppressed state that is characteristic of illness, trauma or emotional distur-

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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bances. They observed that “Based on the discomforts associated with the field situation—the anxiety, fatigue, aches and pains, and assorted other problems—decline of appetite is likely to be a prominent factor in explaining underconsumption of military operational rations. Field training or combat anorexia thus may be the result of a generalized stress response” (IOM, 1995).

The purpose of this paper is to consider appetite control in relation to the high energy expenditure and additional stressors in a combat operation. Apparently, during combat operations, the expected daily energy expenditure is 4,000 to 4,500 kcal, achieved through intermittent periods of high energy expenditure (> 50 percent VO2max) mixed with longer periods of low intensity movement sustained for about 20 h per day. The daily ration must fit within 0.12 cubic feet and weigh 3 pounds or less. The soldiers rely on this ration for three to seven days followed by one to three days of recovery when they will have access to more nutritionally complete meals (i.e., ad libitum food availability served in field kitchen setting). During combat these troops will therefore experience a 1,600 to 2,100 kcal/day energy deficit. This work focuses on these conditions and time window(s). Specifically, the following questions were addressed:

  • Is the energy deficit that soldiers experience in combat due to the relationship between high levels of physical activity, appetite, and energy intake during periods of high energy requirements?

  • How do the additional stresses of combat impinge on appetite and what do we know of the mechanisms?

  • What types of nutritional ingredients or packaging can be added to maintain appetite and hence, presumably, physiological and cognitive performance?

RELATIONSHIP BETWEEN HIGH LEVELS OF PHYSICAL ACTIVITY, APPETITE, AND ENERGY INTAKE

Extremes of Intake and Expenditure

Extremes of energy intake have been recorded during overfeeding studies (Diaz et al., 1992; Norgan and Durnin, 1980; Ravussin et al., 1985), ceremonial overfeeding (Pasquet et al., 1992), prolonged underfeeding studies (Keys et al., 1950), as well as from energy intake records derived from recovering famine, prisoners of war, and concentration camp victims during World War II. These cases represent states of acclimation to extreme environmental conditions, rather than voluntarily energy intake. Compensatory responses subsequent to such induced extremes of energy balance can be spectacular, especially in relation to energy deficits. During rehabilitation from severe malnutrition, famine and concentration camp victims (with body weights below 55 kg) were recorded as spontaneously ingesting 6,900 to 7,900 kcal/day that ceased as body mass and composition were restored.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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TABLE B-19 Effect of Extreme Endurance On Energy Balance In Humans

Study

Nature of the Event

Subjects

Energy Intake (MJ/day)

Energy Expenditure (MJ/day)

Eden and Abernethy, 1994

1,005 km running, 9 days

1 male

25.0

NA

Forbes-Ewan et al., 1989

Military jungle training, 7 days

4

16.9

19.9

Gabel et al., 1995

3,280 km cycling, 10 days

2

29.8

NA

Hoyt et al., 1991

Military mountain training, 11 days

23 males

13.1

20.6

Jones et al., 1993

Military arctic training

10

11.0

18.0

Keys et al., 1950

Ad libitum energy intake post weight loss (25% loss of body weight at first week)

12 males

42.6

NA

Sjodin et al., 1994

Cross-country skiing, 7 days

4 males;

4 females

25.7–36.0;

15.7–20.4

25.4–34.9;

15.1–20.2

Stroud (unpublished results)

Sahara multimarathon, 7 days

4

14.6

22.0–32.5

Stroud, 1987

South Pole expedition, 70 days

3 males

21.0

25–29

Stroud et al., 1993

North Pole expedition, 48 days

2

19.2

28.1–32.4

Stroud et al., 1997

Trans-antarctic expedition:

 

 

Days 0–50;

2 males;

19.9;

29.1–35.5;

 

Days 51–95;

2 males;

22.2;

18.8–23.1;

 

Maximum: days 21–30

2 males

22.2;

46.6–48.7

Westerterp et al., 1986

Tour de France, 20 days

4

24.7

33.7

NOTE: NA = not available.

SOURCE: Adapted from Stroud (1998).

In healthy subjects, such high levels of energy intake have only been recorded under conditions of extreme physical activity such as the Tour de France (Saris, 1989) or military and polar expeditions (Stroud et al., 1993). In the case of the Tour de France, not all the energy intake is voluntary because the participants receive intravenous nutrition during sleep. These examples illustrate the extremes to which energy intake can adapt to intense physiological demands imposed by very high levels of physical activity (Saris, 1989) or severe malnutrition. The primary stressor in these situations is the physical stress of the event. Under these relatively acute conditions in which every attempt is made to meet energy requirements, subjects are nonetheless typically characterized by a marked negative daily energy balance (Table B-19). This is not surprising because this level of expenditure represents the maximal sustainable level of human endurance. In these situations, it is not easy to eat enough to meet elevated expenditures.

The overconsumption characteristic of Western society (with the exception

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

of binging disorders) is not rampant but episodic. Attempting to persuade individuals to continually overeat, even to 150 percent of their maintenance requirements, is actually quite difficult when imposed as an acute change. This has implications for underconsumption in both endurance and military contexts.

Human populations have been known to subsist for quite prolonged periods on extreme ranges of diet composition despite our general tendency to consume 12 to 20 percent of our energy from protein, 35 to 40 percent from fat, and most of the rest from carbohydrate (Mela, 1995). For example, the Inuit have been reported as subsisting for months on high-fat, high-protein diets almost entirely comprising of animal matter and virtually devoid of all carbohydrate (Mowat, 1975). This produces markedly ill effects during lean months when the energy to protein ratio of the diet falls too low. Similarly, the traditional Japanese diet has been reported as constituting some 8 percent of energy intake from dietary fat, in extreme cases. It appears clear from these accounts that human populations are capable of adapting (through their physiological plasticity) to meet their physiological requirements from a wide range of macronutrient ratios in the diet. As indicated by Phinney and collegues (1983a, b) in the case of virtually carbohydrate free diets (< 20 g/day), the period of adaptation can take some days, therefore abrupt, extreme changes in the composition of rations should perhaps be avoided.

The Impact of Altered Energy Expenditure on Energy Intake

When studying the relationship between energy expenditure and energy intake, it is useful to consider how high and low levels of energy expenditure influence intake, and vice versa (Stubbs et al., 2003). The main focus of the present discussion is the relationship between appetite and energy expenditure during high levels of energy turnover. The general population is remarkably sedentary as indicated by cross-sectional surveys of levels of activity among adults and children and the fact that average levels of physical fitness are remarkably low in the population at large (Activity and Health Research, 1992). Black et al. (1996) have estimated from tracer studies that the established limits of total daily energy expenditure ranges from 1.2 to 4.5 times the basic metabolic rate (BMR) over periods of two weeks or more. Intense, sustained activity tends to be a little lower for most people at approximately 2.3 to 2.9 times the BMR, which is similar to combat levels of energy expenditure. For the general, “rather sedentary” population the average daily energy expenditures are in the range of 1.4 to 1.8 times the BMR (Black et al., 1996).

Acute increases in physical activity is believed to promote weight loss (Garrow and Summerbell, 1995). However, this is unlikely to happen over a prolonged period (e.g., Sum et al., 1994). Over time, energy intake will begin to track energy expenditure. The exact manner in which changes in levels of physical activity influence feeding behavior over periods long enough to affect

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

energy balance is not clearly understood. There is a large body of literature on the effect of training programs on body weight and composition in athletes (Barr and Costill, 1992; McGowan et al., 1986; van Baak, 1999; van Etten et al., 1997; Westerterp, 1998). Likewise a number of studies have examined the effects of training programs on weight loss in obese subjects (Saris, 1993; Schoeller et al., 1997). Fewer studies have examined the relationship between changes in energy expenditure and feeding behavior in nonobese subjects who do not have a pre-conceived goal associated with weight reduction or a training program. A review of the effects of exercise regimes on appetite and/or energy intake shows that in short-to medium-term intervention studies (often no longer than two to five days), 19 percent reported an increase in energy intake after exercise; 65 percent showed no change, and 16 percent showed a decrease (Blundell and King, 1999; King et al., 1997). Longer-term studies that measure body composition suggest some fat mass is lost, but lean body mass tends to be preserved in response to exercise regimes, depending on the absolute level of energy balance (Ballor and Poehlman, 1994; Sum et al., 1994). These studies suggest that in the short- to medium-term (1 day to 20 days) energy intake does not accurately track changes in energy expenditure. This raises the critical question: What is the time course over which humans begin to compensate for energy imbalances induced by systematic manipulations of energy intake or of energy expenditure? This is a difficult question to answer because the majority of studies do not track energy intake and energy expenditure on a day-by-day basis. The most precise means of objectively measuring energy expenditure in free-living humans is the doubly labeled water method, which tends to give average estimates of daily energy expenditure over periods of 10 to 20 days (Schoeller and van Santen, 1982). Daily energy expenditure can also be estimated using heart rate monitoring (Ceesay et al., 1989; Spurr et al., 1988), but this technique is widely regarded as having relatively low precision and accuracy, especially with sedentary people (Murgatroyd et al., 1993). However, in studies that employ within-subject comparisons and for which most changes in energy expenditure occur through the same exercise activities that were used to individually calibrate the heart rate monitors, this approach is most efficacious. Stubbs and colleagues (2004b) assessed the effect of no exercise (Nex:control) and high-exercise level (Hex; 4 MJ [955 kcal]/day) and two dietary manipulations, (a high-fat diet [HF]; 50 percent of energy, 167 kcal/100 g) and a low- and high-fat diet [LF]; 20 percent of energy, 71 kcal/100g) on compensatory changes in energy intake and energy expenditure over seven-day periods. Eight lean men were each studied four times, in a 2 × 2 randomized design. Energy intake was directly quantified by weight of food consumed. Energy expenditure was assessed by heart rate monitoring. Body weight was measured daily. Mean daily energy expenditures were 4,200 and 2,750 kcal/day (p < 0.001) on the pooled Hex and Nex treatments, respectively. Energy intake was higher on HF diets (3,200 kcal/day) compared to the LF diets (2,150 kcal/day). Regression analysis showed that these energy imbalances

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

induced significant compensatory changes in energy balances over time of 70 to 96 kcal/day (p < 0.05). These were caused by changes in both energy intake and energy expenditure in the opposite direction to the small changes in energy balance (Figure B-24). These changes were significant and small, but persistent, amounting to approximately 48 and 84 kcal/day for energy intake and energy expenditure, respectively. Under these relatively acute conditions it would take two to four weeks for a person to adjust to the altered level of energy turnover (Stubbs et al., 2004b). However, it is likely that compensation could be accelerated using, for example, sports drinks.

There is evidence that it takes considerable time for energy intake to adjust to elevations of energy expenditure in ad libitum feeding subjects. One direct intervention also supports this view (Figure B-25). Sum et al. (1994) studied the effects of five-month basic military training on body weight, body fat, and lean body mass in 42 Singapore males, classified as being normal weight (BMI 25 to 29.9 kg/m2), obese (BMI 30 to 34.9 kg/m2), and very obese (BMI > 35 kg/m2). Two key features of this study are that training was incremental, allowing subjects to gradually become fitter, and food intake was ad libitum. Over the 5 months of training, fat-free mass (FFM) did not change, but subjects lost substantial amounts of weight and body fat. Subjects who were initially fatter lost more weight and fat. This suggests that responses of intake to exercise-induced changes in energy expenditure may depend on how much fat one has. In other words, it is likely that fat mass is acting as an energy buffer, and intake rises markedly when lean-body mass is threatened by the exercise induced energy deficit. The importance of changes in lean-body mass and appetite control has been discussed by Stubbs and Elia (2001). If responses of intake to exercise-induced changes in energy expenditure depend on body fat level and compensation is due to small changes in both intake and expenditure, then crosstalk between energy expenditure and intake is initially too weak; that is, soldiers would not spontaneously adjust intake to energy requirements during short missions of three to seven days. Most likely, soldiers will need to consciously overcome this lack of spontaneous appetite response by eating more than they feel is sufficient. It appears that substantial fat loss is possible before intake begins to track a sustained elevation of energy expenditure. Friedl (1995) has considered the implications of the baseline nutritional status for physical performance during energy deficit in modern soldiers. Because modern soldiers tend to be larger and better nourished than in earlier studies, they appear to withstand the insults of an energy deficit with less decrement in performance. However, under conditions close to combat (the Ranger I study), “… soldiers who began training with very low body fat (< 10 percent) were less likely to succeed than were slightly fatter soldiers (Moore et al., 1992)” (Friedl, 1995). These data indicate that soldiers who are slightly fatter withstand the rigors of extreme field training better than those who are very lean; they also point to the importance of ensuring soldiers are fed (or overfed) for the coming mission. The Ranger I and II studies provide further

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

FIGURE B-24 Effect of no-exercise, (Nex) and high exercise level [(Hex); (approximately 4 MJ/day)] and two dietary manipulations [a high-fat diet (HF: 50 percent of energy, 700 kJ/100 g) and low-fat diet (LF: 20 percent of energy, 300 kJ/100 g)] on compensatory changes in energy intake (EI) and energy expenditure (EE) over 7 day periods. Eight lean men were each studied four times, in a 2 × 2 randomised design. EI was directly quantified by weight of food consumed. EE was assessed by heart rate monitoring. Top panel gives plots over time for the HF and LF diet conditions. The bottom panel plots energy balance across days for the Hex and Nex conditions.

SOURCE: Stubbs et al. (2004b). Am J Physiol Regul Integr Comp Physiol used with permission.

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

FIGURE B-25 The impact of five-month basic military training on body weight, body fat, and fat-free mass in 42 obese Singapore males.

NOTE: BF = body fat.

SOURCE: Data adapted from Sum et al. (1994).

insights into the time course over which appetite can be suppressed. While energy intake does not accurately track energy expenditure in the short to medium term, over periods of weeks and months, appetite increases again. Friedl (1995) notes that the Ranger students would all have consumed more if food was available and observes that “at least at the extreme level of deprivation of Ranger students (in the studies concerned), there was a strong hunger drive even in the face of multiple stressors” (Friedl, 1995). The same is true of the concentration camp and prisoners of war accounts.

The implications of these data for field training and combat conditions are that (1) when energy expenditure is acutely and significantly elevated, energy intake is slow to respond, and a negative energy balance ensues; (2) the degree of energy deficit will, if continued, compromise physical and cognitive function; (3) use of foods and beverages that are conducive to overconsumption may help limit the extent of the negative energy balance; and (4) if the energy deficit becomes severe over a longer period, appetite will again drive feeding behavior despite multiple stressors (Keys et al., 1950).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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THE IMPORTANCE OF THE RECOVERY PERIOD TO INCREASED FOOD INTAKE

During acute, high levels of energy expenditure, both appetite and energy intake characteristically fail to track elevated energy expenditure (Stubbs et al., 2004a). What is remarkable about these situations is the extent of negative energy balance subjects appear able to sustain, at least in the short to medium term. One factor that is likely to account for the slow response of food intake to increased energy demands is the priority the body has given to the control of water balance. Hypohydration decreases appetite and leads to anorexia (Engell, 1995). Soldiers can lose 3 to 5 percent of body weight during deployment because of the effects of dehydration (IOM, 1995) which may reduce appetite and food intake during combat. In addition, individuals who overfeed tend to be relatively sedentary and relaxed at the time, which obviously is not the case in combat. High levels of activity that redistribute blood flow to the muscles and away from the splanchnic circulation reduce the rate of gastric emptying (Leiper et al., 2001; Mudambo et al., 1997). In addition, there is evidence that dehydration further delays gastric emptying and increases gastrointestinal distress if a person is physically active (running) (Rehrer et al., 1990). Training while consuming carbohydrate-rich beverages may lead to some adaptation in terms of increased or maintained rates of gastric emptying during exercise (Carrio et al., 1989; Rehrer et al., 1992). However, to eat more, one needs to increase to flow of blood to the gut to increase gut motility and digestion of the additional food. It is anecdotally universal that people do not exercise on a full stomach. In summary, the demands of exercise are in conflict with the demands of food intake (e.g., a relaxed meal and increased gut motility). This conflict makes it difficult for a soldier to increase the consumption and digestion of food. It is likely that as with athletes, consumption of readily digested (low-bulk and low-protein) foods and already digested (beverages) nutrients may help bypass this problem. In summary, the decreased blood flow to the gut during conditions of continuous moderate to intense activity, will decrease gut motility and increase indigestion when food is consumed. A limited capacity to increase food intake, coupled with the effects of hypohydration on appetite, results in energy intake that does not effectively track energy expenditure. To rapidly restore energy balance, a sedentary period may be most effective, not just to decrease energy expenditure, but also to facilitate higher levels of energy intake such as refeeding between missions. It is no coincidence that during the Guru-Walla overfeeding ritual, the subjects remain entirely sedentary during a period when they consumed some 6,000 to 7,000 kcal/day (Pasquet et al., 1992). The little evidence available relating to abrupt decreases in energy expenditure caused by training cessation or injury suggests that reduced activity leads to acute decreases in energy expenditure, that then leads to reduced activity marked by gain in body weight. Figure B-26 indicates that reduced energy expenditure from inactivity is very weakly linked, through

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
×

FIGURE B-26 Mean (standard error of means) cumulative energy balance (MJ) for six men who were continually resident in a whole-body indirect calorimeter for 7 days on either a sedentary or active treatment. On the sedentary treatment, daily energy expenditure was held at 1.4 × BMR (the low end of the sedentary range), and on the active treatment daily energy expenditure was held at 1.8 × BMR. Subjects were fed ad libitum throughout on a medium-fat diet of constant measurable composition.

NOTE: BMR = basal metabolic rate.

SOURCE: Stubbs et al. (2004a) Am J Physiol Regul Integr Comp Physiol used with permission.

physiological signals, to energy intake and has little effect in reducing intake (Stubbs et al., 2004a). A period of rest may promote greater levels of energy intake by providing opportunities and a physiological capacity for overconsumption. Thus, refeeding soldiers during recovery periods should be considered; it may be somewhat harder to supplement them during acute elevations of activity. In addition to these problems for appetite control, the soldiers are subjected to a variable range of stressors that do not generally occur during attend athletic and endurance events. This raises the question: Is all of the negative energy balance observed under combat conditions entirely due to the relationship between increased exercise and appetite?

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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EFFECTS OF ADDITIONAL COMBAT STRESSORS ON APPETITE

Stresses Associated with Combat
Hypohydration

A major stress of deployment and combat is hypohydration. This is not necessarily related to levels of energy expenditure. Soldiers appear particularly susceptible to hypohydration during deployment, in hot environments, and where they are required to wear protective clothing (IOM, 1995). The CMNR considered that a weight loss of > 3 percent and < 10 percent was principally due to an inadequate fluid intake, which would likely reduce performance (IOM, 1995). Engell (1995) has reviewed the evidence that shows inadequate water intake restricts ad libitum food intake. The converse does not appear to be true. Figure B-27 shows the effects of changes in the composition of the diet on ad libitum daily energy intake in 78 subjects self-recording their own food intake (Stubbs et al., 2000). Large variations in water intake, presumably in well-hydrated people, have little effect on energy intake. Given the likelihood of hypohydration and its effects on energy intake, it is critical that attempts are made to avoid this stress and its knock on effects for appetite and performance.

FIGURE B-27 Relationship between energy density (ED) of the diet (expressed as a daily percentage of the maximum daily ED of each subject’s diet) and energy intake (EI) in 76 subjects self-recording their food intake by weighed dietary record over 7 consecutive days. Subjects with energy intakes < 1.2 × BMR who did not lose weight during the seven days were previously excluded.

NOTE: BMR = basal metabolic rate.

SOURCE: Stubbs et al. (2000).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Sleep Deprivation

Another stress of combat is sleep deprivation. In rats sleep deprivation appears to cause an increase in locomotor behaviour, and increase in food intake, and increase in the activity of the hypothalamic-pituitary-adrenal axis (increased plasma thyroxine, norepinephrine) and increased heat loss (Rechtschaffen et al., 2002), leading to considerable loss of function and even death. These problems may relate to altered thermoregulation. In rats sleep deprivation causes malnutrition (despite the increased energy intake), which is secondary to increased energy expenditure (Everson and Wehr, 1993). Horne (1985) has noted that the extreme problems of thermoregulation, induced by sleep deprivation in rodents, do not appear to apply to humans. Many studies relevant to military situations also include periods of intense activity (e.g., Oektedalen et al., 1982; Opstad and Aakvaag, 1981; Opstad et al., 1984) and it is difficult to separate the effects of a negative energy balance induced by sleep deprivation or by exercise. Akerstedt et al. (1980) exposed twelve healthy males to 48 h of sleep deprivation under conditions where time isolation and activity and feeding were strictly controlled. They found that under these otherwise unstressed conditions adrenocortical and gonadal steroid hormones were lower or unchanged, indicating a lack of emergency stress response, due to sleep deprivation. Redwine et al. (2000) have found that mild sleep deprivation affects IL (interleukin)-6 levels, suggesting sleep deprivation may influence the integrity of immune functioning. The cognitive effects of sleep deprivation are documented elsewhere (Foo et al., 1994; Fu and Ma, 2000). It seems that sleep deprivation induces a negative energy balance (due to increased activity that causes the lack of sleep) and obviously, fatigue. In rats at least, these changes are alleviated better with supplements of energy than of protein (Everson and Wehr, 1993). There is no clear evidence that sleep deprivation decreases appetite and energy intake; on the contrary, in rats it appears to increase energy intake. However, in both rats and humans, under the disparate conditions of the studies conducted, intake does not appear to match elevated energy requirements associated with sleep deprivation. It is not clear why this is so, particularly when the limited indications are that supplemental energy intakes may alleviate some of the stress of sleep deprivation.

Anxiety

There is no doubt that the combat environment induces the most extraordinary levels of anxiety. The modernization of warfare methods increases stress, anxiety and emotional trauma, which have an acute effect at decreasing appetite. These levels of stress are rarely quantified, but they have been documented in the diaries and records of numerous soldiers throughout humankind’s continuing and ongoing conduct of various wars. In several classical accounts, especially those associated with the D-Day landings when there was a period of prebattle

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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anticipation, the inability to eat or even hold food down was not uncommon (see accounts at http://www.bbc.co.uk/dna/ww2/C54665). Some of these disturbances remain after the war is over as combat-stress disorder and posttraumatic stress disorder, as documented by a growing literature (Hyams et al., 1996; Pearn, 2000; Pereira, 2002; Witztum et al., 1996).

Stress-Related Mechanisms of Appetite Suppression

Stress-related mechanisms of appetite suppression are multiple, redundant, and poorly understood in humans. In rats, hypohydration-induced anorexia appears to involve corticotrophin releasing factor and neurotensin in the lateral hypothalamus (Watts, 1999). Brain stem mechanisms are also involved (Flynn et al., 1995). Sleep deprivation will clearly affect the peptide families controlling biorhythms, which may disrupt diurnal patterns of feeding. Anxiety-based responses will be mediated through the hypothalamic-pituitary-adrenal axis and inflammation/physical trauma will be mediated by the immune-inflammatory system (Newsholme and Leach, 1992). Most evidence is derived from animal models except for the growing body of psychological evidence relating to human stress. Because of the wide range of components of these responses, there is no simple stress-associated mechanism that can be alleviated by a simple nutritional or pharmacological manipulation to improve appetite. While the interactions of these different components are unknown, it is reasonable to conclude that together, they will decrease appetite under combat situations. The intuitive solution would be to minimize the perception of satiety. It is important to supplement rations with energy because as a negative energy balance proceeds, performance will deteriorate and appetite will increase, even under stressed conditions [see Keys et al. (1950) for consideration of responses to undernutrition in war].

When and When Not to Bypass Satiety

When considering strategies to bypass the decreased appetite associated with combat, one can gain insights by analogy with clinical conditions. In the clinical setting under conditions of severe stress, such as surgery and shock, the patient experiences a period of catabolism, during which inter alia plasma glucagon, coticosteriods, and catecholamines are elevated. These are all hormones that induce an acute negative nitrogen balance and raise plasma glucose, providing metabolic fuels to deal with the stress at hand (Newsholme and Leach, 1992). Under these conditions, appetite is also characteristically suppressed and there is some debate as to whether supplementation should occur ever be provided through enteral or parenteral nutrition. This is important because a number of the stresses to which soldiers are exposed on the battlefield (beyond the obvious injuries and risks) may well be similar, in extent, to those experienced during shock, trauma, or other illness in the clinical setting. Under these conditions

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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people are intolerant of food in the following three ways: (1) appetite suppression; (2) increased gastric stasis (decreased gastric emptying) caused by intense exercise, acute systemic injury, or postoperative stress; and (3) intolerance to specific nutrients during stress (Newsholme and Leach, 1992).

The following examples illustrate how the use of bioactive substances to improve clinical outcomes can produce unpredictable serious side-effects, including death. The first example involves injections of pharmacological doses of growth hormone (GH) in critically ill patients. It was thought that GH might be beneficial by limiting the marked nitrogen loss that frequently occurs in such patients (equivalent to overcoming a metabolic block in net protein synthesis). Growth hormone is known to stimulate protein synthesis and had previously been shown to improve nitrogen balance in a wide range of clinical conditions. However, in a large multicenter trial involving patients admitted to intensive care units, pharmacological doses of GH doubled (from about 20 percent to 40 percent) mortality as compared with the placebo group. Although the mechanisms responsible for the increased mortality are still uncertain, several suggestions have been made (Takala et al., 1999).

A second example shows how outcomes in the critically ill can be improved through the control of delivered nutrients. The importance of strict glucose homeostasis in critically ill patients was demonstrated by a large study involving about 1,500 patients who were randomized to receive insulin to control their plasma glucose concentrations strictly between 4.4 and 6.1 mmol/L, or to receive standard therapy in which a circulating concentration of 10.0 to 11.1 mmol/L was considered acceptable. In the strictly controlled group there was a four-fold reduction in mortality and a two-fold reduction in the number of transfusions and the incidence of critical care polyneuropathy (van den Berghe et al., 2001). Thus, the use of bioactive ingredients and nutrients to bypass suppressed appetite must be considered with caution under conditions of acute and unpredictable stress. The nature and extent of the stress will be important in determining tolerance to the supplement.

It is known that during military training and combat, the rate, extent, and composition of weight loss influence physical performance and cognitive function (Freidl, 1995). We know from these studies that protein is largely adequate and mineral and vitamin short-term deficits are well tolerated under field conditions (Baker-Fulco, 1995). The main purpose of supplementation is to overcome suppressed appetite and meet, as closely as possible, energy and fluid requirements. The timing of energy supplementation is likely to have a large impact on tolerability and, indirectly, on performance. Most evidence about stress and tolerability of rations is derived from noncombat conditions in which the most acute stressors are largely absent. It is perhaps necessary to ascertain under combat or similar conditions how different stressors will influence appetite and physiological and cognitive function. From a research perspective, the authors suggest it is important to: (1) quantify the likely nature and extent of the stress

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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under combat or similar conditions; (2) test strategies to optimize energy intake before, after, or during combat (with focus on timing and composition of the supplement); and (3) quantify the tolerability and performance response. From the perspectives of both appetite and performance, timing and composition are the two critical features of the ration that determine the benefits of supplementation. Timing is important because it will determine the most efficacious and feasible strategy of supplementation. Composition of foods influences the amount that can be ingested (Stubbs, 1998; Stubbs et al., 1995, 2001).

NUTRITIONAL INGREDIENTS OR PACKAGING TO MAINTAIN APPETITE

Diet Composition and Appetite

A number of reviews have considered the means and mechanisms by which dietary macronutrients, macronutrient substitutes, and associated nutritional parameters, such as dietary energy density influence appetite and energy balance in humans (Stubbs, 1998; Stubbs et al., 2000). As they exist in the diet, macronutrients differ in their metabolisable energy coefficients (Elia and Livesey, 1992). Average values for alcohol, protein, carbohydrate, and fat are 7, 4, 4, and 9 kcal/g. Fat and alcohol are more energy dense (energy per wet weight of food eaten) than protein and carbohydrate (Elia and Livesey, 1992).

Not all of the different macronutrients affect satiety to the same degree. There is a hierarchy in the satiating efficiency of the macronutrients such that, under a variety conditions per unit of energy ingested, protein suppresses appetite to a greater extent than carbohydrate, which has a greater effect than fat (Stubbs, 1995; Figure B-28). Caloric compensation can be defined as a unit decrease in energy intake for each unit of energy given as a particular nutrient. Protein produces supercaloric compensation, carbohydrate caloric compensation and fat ingestion leads to subcaloric compensation (Figure B-27). Thus, high-protein diets are particularly satiating and limit energy intake. Because of this, foods conducive to a high-energy intake tend to be low in protein. When ingested at the same level of energy density, protein is still the most satiating macronutrient (Johnstone et al., 1996; Stubbs et al., 1996). Under these conditions differences between carbohydrate and fat are less clear cut. Carbohydrate tends to exert a more acute effect on satiety than does fat (Johnstone et al., 1996; Stubbs et al., 1996).

Dietary energy density tends to act as a constraint on feeding behavior (Stubbs et al., 2000). A diet that has too low-an energy density will induce an energy deficit determined by the rate at which low-energy-dense foods can be digested and absorbed. There is evidence that food intake will increase in the longer term to offset this deficit. With high energy density diet, overconsumption tends to occur because the amount of food a person eats tends to be conditioned and weak against excess energy intake (Stubbs et al., 2000).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Because of its contribution to energy density, fat is often seen as the nutrient that will induce the greatest energy intake. It is possible to produce maltodextrin supplements that produce equally large elevations of energy intake (Stubbs et al., 1997, 2001). Very active subjects can also benefit from water that is stored with glycogen in a 3:1 ratio. Given that hydration is critical to troops in combat, the ability to carry water locked in glycogen may help alleviate hypohydration-induced anorexia.

Certain types of protein, carbohydrates, and fat may exert different effects on appetite (Stubbs et al., 1999) but this is a relatively new area. Current evidence suggests that sweet, wet, carbohydrate solutions induce lower caloric compensation (i.e., facilitate supplementation) than the same carbohydrates given as solid foods (diMeglio and Mattes, 2000; Stubbs et al., 2001). Women soldiers consume more when given ready access to commercial snack foods (Rose, 1989). This raises an

FIGURE B-28 Effect of increasing the energy content of macronutrient loads on Satiety Index subjectively expressed over 3.25 h.

SOURCE: Weststrate (1992).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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important research issue of whether energy-dense dry foods (rich in fats and sugars) will elevate energy intake more than lower energy-dense beverages (rich in carbohydrates). In this context the hydration status of the subject is likely to be critical. Another question is raised about the effects of consumption of foods that require minimal digestion and place minimal stress on the gut, like athletes do (see above).

According to our data, large amounts of water intake in well-hydrated subjects will displace little or no energy from the diet (Figure B-27; Stubbs et al., 2001). Energy-containing beverages appear to have a supplemental effect. Stratton et al. (2003) showed that using a continuously infusing naso-gastric drip, it is possible to increment daily energy intake by approximately 1,000 kcal/day in ad libitum, free-living, well-hydrated subjects. These observations support the CMNR suggestions (IOM, 1995) that increased snacking and beverage intake may help elevate energy intake in the field.

Possible Strategies to Elevate Energy Intake and Performance in Combat
Timing

We know that loss of weight, especially as water and/or lean tissue, can be detrimental to performance in combat. Given that even in a 60-day Ranger study (Moore et al., 1992) during which subjects were in an energy deficit, approximately 1,200 kcal/day subjects who had < 10 percent body fat performed less well than slightly fatter subjects, soldiers with even relatively small amounts of extra body fat may have certain performance advantages in combat. This will be more so if the stressors are such that neither opportunity nor motivational appetite facilitate food intake. It would be valuable to compare the effects of overfeeding subjects before combat or during resting periods with the effects of supplemention during combat. One way to optimize nutritional status and hence performance in combat is to focus on supplementation during those recovery periods. A major research question is: When could energy be supplemented to achieve the best results?

Ingredients

During deployment it may be advantageous to supplement troops with carbohydrate-rich beverages to avoid hypohydration. In addition, the extra water stored with glycogen will act as a small internal water reservoir. It is our opinion that the most effective way to supplement a person that has free-living, ad libitum feeding is to trickle readily assimilated energy by using small snacks and beverages; such design also provides greater flexibility than a pack of three Meals, Ready-to-Eat (MREs). The use of flavor enhancers has had remarkable effects on soft drink sales and intakes. It is likely that soft drinks will readily replace the

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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fluid and carbohydrate requirement for performance if the problems of portability can be overcome (see below).

Given the high satiety value of protein and, to a lesser extent, fiber’s negative association with energy density, these components of foods are not conducive to high energy intakes. Similarly, very high-fat food items on their own might also be avoided because there is evidence that fat loads can enhance satiety at the level of the gut (Welch et al., 1988), an effect to be avoided in combat. On the other hand, except when in cold environments (Stroud et al., 1993), satiety with low food consumption is desirable to minimize gastrointestinal disturbances. Mixtures of fats and carbohydrates are particularly conducive to overconsumption as indicated by the fact that most commercial snacks are of this composition (Holland et al., 1991).

Portion Size

Previous authors have suggested that maximizing portion size will help elevate energy intake in the field setting (Rolls, 1995). In combat, however, a greater number of smaller portions will facilitate snacking and maintain energy levels. In terms of the pattern of daily intake, it is pertinent to note that meal size actually increases through the day. On average, breakfast is smaller than lunch, which is smaller than dinner (de Castro, 2000). In our experience, when offered three meals equal in size and energy content for breakfast, lunch, and dinner, subjects complain that breakfast is too large and dinner is too small. This may contribute to underconsumption of MREs because troops are unlikely to save half of one ration until later.

Packaging

A good deal of work has already been done on the way variety, packaging, and social and situational influences may help enhance intake during field training and combat (see IOM, 1995). In particular, some of the modeling approaches and marketing techniques used in commerce (Thompson, 1995) may be of considerable value in raising expectation and acceptability of rations. Companies use a variety of messages to repeatedly maintain consumer interest in their products, and it has already been shown that troops consume more if military rations are packed in a manner that resembles commercial products (Kalick, 1992; Kramer et al., 1989). There may be value in adding food-based aromas to foods to enhance their appeal given the influence of aromas in taste perceptions. After Desert Storm, many commanders expressed their belief in the importance of hot cooked food with an appealing aroma as being vital to morale (see IOM, 1995). While this luxury may not be available in combat, it should be a priority between missions.

Given the problems of hydration and food portability, the new packaging

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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developments are of critical importance. The new packaging provides a remarkable system whereby a variety of water sources, including a filtration of one’s own urine, can safely be ingested. A range of super-soluble, low-weight supplements could be mixed with water, thus replacing fluid, electrolytes, and glucose under conditions during which other rations cannot be consumed.

It may be valuable, in addition, to develop tools whereby soldiers can monitor their own fluid and fuel status (in that order). Dehydration can be assessed with urine sticks, and this may provide rapid feedback to soldiers who may not be experiencing the usual urges to eat and drink.

RESEARCH

Given the extreme energy deficit encountered in combat, nutritional supplementation should be the primary focus of rations for soldiers in short-term, high-intensity operations. We have provisionally recommended that research be focused on (1) better understanding of the nature and extent of stressors experienced in combat; (2) determining the optimum timing for nutritional supplementation (including between missions), bearing in mind that supplementation during unpredictable stress may not be advantageous; and (3) finding the most effective means of bypassing suppressed appetite to maintain hydration and optimize energy intake for performance in combat. More data derived from combat or similar situations on the nature of stress, types of intervention, and outcome would be valuable but difficult to obtain. Assessing how initial body composition relates to performance during extreme field training (e.g., Ranger I study) would help to derive guides for feeding before combat.

CONCLUSIONS

Three basic questions regarding the relationship of stress and appetite have been considered. First, in considering the relationship between energy intake and expenditure, it is apparent that appetite poorly tracks acute and extreme elevations of exercise-induced energy expenditure. This might be partly due to the fact that hypohydration itself induces anorexia. Behavior should be geared first to fluid ingestion and then to energy balance. In addition, intense exercise influences gastrointestinal physiology and blood flow and decreases gastric emptying. Hypohydration makes these effects more acute. Under conditions in which increased gastric emptying is needed (i.e, greater food intake), in addition to indigestion, a conflict between the demands of eating and those of exercising will occur. In the short- to medium-term, eating can limit exercise, but exercise can continue without necessarily consuming more thus intake will fail to track expenditure. The best approach to this low energy intake under these circumstances is to consume readily digestable energy and carbohydrate-rich beverages.

Second, the additional stressors of combat may exert further suppressive

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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effects on appetite and have been considered; however, the nature and extent of these stressors is highly unpredictable. The general rule in the clinical setting is that during periods of extreme metabolic instability, do not feed. It is critical to quantify the nature and effects of combat-related stresses and the way they affect both appetite and performance.

Third, other factors such as timing, type of ingredients, and packaging have been considered. When combat is likely to involve extreme stressors, it may be more advantageous to supplement soldiers before deployment and postmission and to maintain fluid and energy (carbohydrate) intakes during acute phases of combat. We suggest that research priorities in this area should focus on quantifying the nature and extent of stressors experienced in combat and their effects on physical and cognitive performance; in addition, assessing the effects of timing, and determing the composition of supplements to improve performance in combat should be a priority.

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Optimization of Immune Function in Military Personnel

Simin Nikbin Meydani and Faria Eksir, Tufts University

INTRODUCTION

Although moderate amount of exercise could result in improving the immune function, it has been shown that strenuous physical activity can suppress the immune response (Hoffman-Goetz and Pedersen, 1994). Studies have reported that during combat as well as during times of rigorous training, soldiers are

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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exposed to many types of stress factors that can affect different components of the immune system (Moore et al., 1992). Lack of sleep, low energy food ration, and psychological stress are among those factors that contribute to a low immune response. The fact that during military work, soldiers are often exposed to long durations of strenuous physical activity, makes the danger even more serious. The duration of physical stress as well as the low energy intake that is associated with military life can cause severe alterations in the immune response and increase risk of infection among soldiers. Many studies have been conducted on the effects of individual stress factors on the immune function. A few studies have shown that the combined effect of the stress factors can be even more damaging to the immune response than the effect of each individual factor (Booth et al., 2003; Kramer et al., 1997).

Immunological studies conducted on military personnel have reported several unfavorable consequences resulting from stresses associated with military life. A major concern has to do with the low-calorie food ration provided for soldiers in combat. Studies have well documented the impact of dietary intake on physical performance and on the immune response (Booth, 2003; Montain and Young, 2003). Undernutrition and/or malnutrition, especially during stressful times, can result in suppression of the immune response, which can lead to increased susceptibility to infection (particularly respiratory infection) and diarrheal diseases often experienced by combat personnel. In fact, it has been documented that during combat, diseases account for more inactive days than either combat wounds or nonbattle injury cases among military personnel. The question would be: What measures can be taken to ameliorate the situation for our military personnel? Clearly, reducing the level of stress would be an effective course. However, given the nature of the job, in all likelihood, that is also the most unattainable option. A more feasible choice would be to conduct vaccinations against various possible diseases, a practice that already has been taken up by the military sectors. Still, available vaccinations only protect against certain diseases and do not provide protection against new pathogens to which the soldiers would likely be exposed. In addition, the vaccines are less effective in immuno-suppressed individuals. An effective and more promising means of protecting the immune function during combat would be through an optimal nutrition plan, which is the focus of this paper. The specific questions that this paper addresses are the following:

  • What links are known to exist between nutritional factors and the optimization of the immune system? Specifically which nutritional factors would help reduce occurrence of infections or enhance disease resistance?

  • Are there consequences on immune function from a short-term hypocaloric diet?

  • Are there nutrients that might improve resistance to infection despite a hypocaloric diet?

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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NUTRITIONAL STRATEGIES TO IMPROVE THE IMMUNE RESPONSE

Most nutrient deficiencies result in the impairment of the host defense system and increase susceptibility to infectious diseases (Chandra and Sarchielli, 1993; Keusch et al., 1983). Additionally, recent studies have shown that malnutrition, such as deficiency of selenium and vitamin E, plays a major role in increasing the pathogenicity of microbes and surfacing of unusual viral infections (Beck and Levander, 1998). This is quite important in the case of soldiers at combat in foreign lands, because they frequently encounter pathogens that they have not previously been exposed to. A strong host defense system is critical in the ability of the body to fight off novel pathogens and develop an immune response for future attacks. Supplying the soldiers with adequate nutrients could reduce the risk of a suppressed immune response. Furthermore, providing more than adequate levels of some nutrients can strengthen the immune function and protect against infection and disease.

Using animal models, a number of studies have demonstrated the role of micronutrients (vitamins and trace minerals) in enhancing the immune function. However, studies of micronutrients and immune function in human subjects have been limited and very few have looked at the effect of nutrients on disease and susceptibility to infection. Recently, however, a few studies have examined the relationship between nutritional deficit and/or supplementation and disease in the elderly population.

It should be noted that in spite of the chronological age difference between the elderly population and the military personnel (mostly consisting of a young population), there are similarities in their immune systems. In both groups, the elderly and the military personnel in combat, immunosuppression is evident and characterized by a decrease in cell-mediated immunity and changes in the ability of lymphocytes to proliferate. Notably, the elderly, as a consequence of immunological changes, have a higher susceptibility to, and a greater morbidity and mortality from, infectious diseases, particularly respiratory infections and diarrheal diseases, which are some of the major concerns for soldiers in combat as well. Thus, in the absence of data for military combat personnel, results from a recent clinical trial on vitamin E and respiratory infections will be reviewed as an example of how nutrient intervention could be used to optimize the immune response and reduce risk of infection in an immunocompromised individual.

VITAMIN E AND INFECTIOUS DISEASES

The immunostimulatory effect of vitamin E has been shown to be associated with resistance to infections. Most of the animal studies that investigated the effects of vitamin E on infectious diseases reported a protective effect despite the variations in the dose and duration of the supplementation, infectious organisms involved, and route of administration as reviewed by Meydani et al. (2001).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.
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Vitamin E supplementation in old mice resulted in significantly lower viral titer and preserved antioxidant nutrient status following influenza virus infection (Hayek et al., 1997). This protective effect of vitamin E against influenza infection seems to be partly due to enhancement of Th1 (T helper 1) response, increased IL (interleukin)-2 and IFN-γ production (Han et al., 2000).

VITAMIN E AND RESPIRATORY INFECTIONS IN THE ELDERLY

Only a limited number of studies have investigated the effect of vitamin E on resistance against infections in humans. The subjects in these studies were mainly elderly persons. Infections, particularly respiratory infections (RI), are common in the elderly, resulting in decreased daily activity, prolonged recovery times, increased health care service use, and more frequent complications that may lead to death (Alvarez et al., 1988; Crossley and Peterson, 1996; Farber et al., 1984; Garibaldi et al., 1981; Gugliotti, 1987; Hasley et al., 1993; Jackson et al., 1992; Mehr et al., 1992; Nicolle et al., 1984; Plewa, 1990; Schneider, 1983). Contributing to the increased incidence of infection with age is the well-described decline in immune response (Siskind, 1980). For example, there are higher morbidity and mortality from cancer, pneumonia, and postoperative complications in those who have a diminished delayed-type hypersensitivity (DTH) skin test response (Christou et al., 1989; Cohn et al., 1983; Wayne et al., 1990).

Nutritional status is an important determinant of immune function (Chandra, 1990; Keusch et al., 1983), and nutritional supplementation has been shown to enhance older subjects’ immune response (Chandra, 1992; Meydani and Blumberg, 1989). In our earlier placebo-controlled, double-blind trials in elderly persons, vitamin E supplementation improved immune response, including DTH and response to vaccines (Meydani et al., 1990, 1997). In this study we also reported a nonsignificant (p < 0.09) 30 percent lower incidence of self-reported infections among the groups supplemented with vitamin E (60, 200, or 800 mg/day for 235 days) compared with the placebo group (Meydani et al., 1997). Because infection was not the primary outcome, the study did not have enough power to detect significant differences in the incidence of infections. To overcome these limitations, we conducted a large double-blind, placebo-controlled trial to determine the effect of one-year supplementation with vitamin E on objectively recorded respiratory illnesses in elderly nursing home residents (Meydani et al., 2004).

In this randomized, double-blind study, 617 people older than 65 and residing at 33 nursing homes in the Boston area who met the study’s eligibility criteria received either a placebo or 200 IU of vitamin E (dl-α-tocopherol) daily for one year. All participants received a capsule containing half the recommended daily allowance of essential vitamins and minerals. The main outcomes of the study were incidence of respiratory tract infections, number of persons and number of days with RIs (upper and lower), and number of new antibiotic prescriptions for RIs among all randomized participants and those who completed the study (Meydani et al., 2004).

Suggested Citation:"Appendix B: Workshop Papers." Institute of Medicine. 2006. Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations. Washington, DC: The National Academies Press. doi: 10.17226/11325.