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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations 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
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations 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.
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations 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,
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations 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
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations 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
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations BOX B-1 Questions to Be Addressed by CMNR Workshop on Optimization of Nutrient Composition of Military Rations for Short-Term, High-Stress Situations 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? What is the optimal macronutrient distribution (protein, fat, and carbohydrate) for the FSR to best sustain and/or enhance performance during combat missions? 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? 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? 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: Component packaging, types, sizing, flavors Bioavailability factors 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
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations 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.
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations 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),
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations 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.
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations 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
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations 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
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations Santangelo A, Peracchi M, Conte D, Fraquelli M, Porrini M. 1998. Physical state of meal affects gastric emptying, cholecystokinin release and satiety. Br J Nutr 80(6):521–527. Shields DH, Corrales KM, Metallinos-Katsaras E. 2004. Gourmet coffee beverage consumption among college women. J Am Diet Assoc 104(4):650–653. Shimizu H, Tsuchiya T, Sato N, Shimomura Y, Kobayashi I, Mori M. 1998. Troglitazone reduces plasma leptin concentration but increases hunger in NIDDM patients. Diabetes Care 21(9):1470–1474. Stockley L, Jones FA, Broadhurst AJ. 1984. The effects of moderate protein or energy supplements on subsequent nutrient intake in man. Appetite 5(3):209–219. Stubbs RJ, Prentice AM, James WP. 1997. Carbohydrates and energy balance. Ann NY Acad Sci 819:44–69. Stubbs RJ, van Wyk MC, Johnstone AM, Harbron CG. 1996. Breakfasts high in protein, fat or carbohydrate: Effect on within-day appetite and energy balance. Eur J Clin Nutr 50(7):409–417. Sunkin S, Garrow JS. 1982. The satiety value of protein. Hum Nutr Appl Nutr 36(3):197–201. Tordoff MG, Alleva AM. 1990. Effect of drinking soda sweetened with aspartame or high-fructose corn syrup on food intake and body weight. Am J Clin Nutr 51(6):963–969. Tournier A, Louis-Sylvestre J. 1991. Effect of the physical state of a food on subsequent intake in human subjects. Appetite 169(1):17–24. Vandewater K, Vickers Z. 1996. Higher-protein foods produce greater sensory-specific satiety. Physiol Behav 59(3):579–583. Williams JA, Lai CS, Corwin H, Ma Y, Maki KC, Garleb KA, Wolf BW. 2004. Inclusion of guar gum and alginate into a crispy bar improves postprandial glycemia in humans. J Nutr 134(4):886–889. Wolf BW, Wolever TMS, Lai CS, Bolognesi C, Radmard R, Maharry KS, Garleb KA, Hertzler SR, Firkins JL. 2003. Effects of a beverage containing an enzymatically induced-viscosity dietary fiber, with or without fructose, on the postprandial glycemic response to a high glycemic index food in humans. Eur J Clin Nutr 57(9):1120–1127. Wooley OW, Wooley SC, Dunham RB. 1972. Can calories be perceived and do they affect hunger in obese and nonobese humans? J Comp Physiol Psychol 80(2):250–258. A General Model of Intake Regulation: Diurnal and Dietary Composition Components John M. de Castro, University of Texas at El Paso INTRODUCTION A considerable amount of evidence shows that nutrient intakes are affected by a wide range of factors, each of which accounts for only a small portion of the variance in intake. Models that attempt to explain intake control based on any single factor have failed to account for how intake can be controlled in the face of a complex array of influential variables. In addition, the levels and effects of many factors vary from individual to individual, and these individual differences are affected by heredity. These elements have been incorporated into a general model of intake regulation (de Castro and Plunkett, 2002) that is presented in Figure B-49. The model separates sets of uncompensated and compensated factors
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations FIGURE B-49 The general intake regulation model wherein intake (I) is controlled by two sets of factors: compensated factors (Ci) that both affect and are affected by intake via negative feedback loops and uncompensated factors (Ui) that affect but are not affected by intake. Inheritance affects the system by (a) determining the preferred level for intake and compensated and uncompensated factors and (b) determining the level of impact of the factors on intake (W). Factors that are affected by heredity are indicated in bold. SOURCE: de Castro and Plunkett (2002), used with permission from Elsevier. with each factor having preferred levels that are influenced by heredity (e.g., genetic variation). Further, the model specifies that each factor in both sets has an individual impact factor (i.e., weight that specifies the magnitude of the factor’s effect on intake). The weights are assumed to be different for each individual, and their values are influenced by heredity. Simulations of the model indicate that although prolonged changes in the level of any factor can result in a prolonged change in intake and body weight, the size of the change depends on the inherited level of responsiveness to that factor. This implies that manipulation of a factor to alter intake will be effective in some individuals but not in others. For this reason, it is important to consider individual differences in responsiveness when developing an intervention designed to alter intake. The responsiveness of the individual to these influences can be measured and used to help construct an individualized intake recommendation. The Committee on Committee on Optimization of Nutrient Composition of Military Rations for Short-Term, High-Stress Situations was charged with designing the nutrient composition of a ration to be used for short-term, high-stress combat operations. It is a well-known fact that the energy intake of soldiers in these unique situations of high mental and physical stress is lower than the energy expenditure, and this energy deficit status might result in weight losses and other health and perfomance adverse effects. In addition to maintaining health and performance, the ration should be palatable and accepted by soldiers under such unique circumstances. Palatability is only one factor that drives consumption patterns; other factors that might be categorized as psychological factors are also important in defining eating behavior, including level of consumption. In this paper, the role of diurnal rhythms and dietary energy density on dietary intake behavior is examined; the conclusions are derived with data from
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations reports from 669 free-living normal adult humans who adequately reported intake in a 7-day diet diary. The influence of the time of day and the dietary energy densities on intake were investigated. This model could be applied to soldiers under combat situations. Specifically, this paper attempts to answer the following questions: What are the food factors, which regulate food intake, that could maximize the consumption of a food ration given to soldiers under physical, cognitive, and environmental stresses? What are the issues to consider when developing a nutritionally enhanced food product in terms of energy density, satiability, behavior and food characteristics to maximize the consumption of the food product in specific relation to soldiers under stress? DIURNAL FOOD INTAKE PATTERN There are clear diurnal or circadian influences on intake. Studies using the diet diary technique (de Castro, 1987, 2004c) have demonstrated that substantial changes in intake occur over the course of the day. As the day progresses, the average meal size increases (Figure B-50, left) and the subsequent interval between meals decreases simultaneously (Figure B-50, center). We have found that this pattern is true for both North Americans and Europeans (de Castro et al., 2000) as determined by using the satiety ratio. The satiety ratio is the duration of the interval after the meal divided by the meal size (min/MJ), and it gauges the duration of satiety produced per unit of food energy ingested. This ratio markedly declines over the course of the day and becomes quite low during the late evening (Figure B-50, right) (de Castro, 1987, 2004c). This suggests that the satiating effect of food decreases over the course of the day and that a large proportion of intake in the evening could lead to increased overall intake. Employing twin data, it was demonstrated that the time of day when people eat is significantly affected by heredity (de Castro, 2001). In particular, people differ in the proportion of daily intake ingested at different times of the day, with some eating a larger proportion of their intake in the morning, some in the afternoon, and some in the evening, and these proportions of intake are heritable. It was also demonstrated that the differences between the morning and afternoon, the morning and evening, and the afternoon and evening were significantly heritable (de Castro, 2001). This suggests that the time-of-day effects on intake vary among individuals and that this difference is, at least, partially caused by heredity. Hence genetic factors appear to affect not only when an individual will tend to eat, but also how big of an effect the selection of that time will have on intake. Because meal sizes increase during the day, while the after-meal intervals and satiety ratios decrease over the day, it is reasonable to expect that the time of day of nutrient intake would be related to total intake. It was demonstrated that
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations FIGURE B-50 The mean meal sizes (left panel), interval until the following meal (middle panel), and the satiety ratio (right panel) observed during the morning, afternoon, and evening periods. SOURCE: Adapted from de Castro (2004c).
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations FIGURE B-51 Correlation between proportion of intake during four-hour periods and overall daily intake. The mean correlations between the proportions of food energy ingested and overall daily intake were self-reported in 7 day diet diaries during each of the five time periods and the total amount ingested. NOTE: *Different from zero (p< 0.01). SOURCE: Adapted from de Castro (2004c). the proportion of intake ingested in the morning is negatively correlated with overall intake (Figure B-51), while the proportion ingested late in the evening is positively correlated with overall intake (de Castro, 2004c). The energy densities of intake during all periods of the day were positively related to overall intake. The results suggest that a high-density energy intake during any portion of the day could increase overall intake and that an intake in the late night lacks satiating value and can result in greater overall daily intake. Hence the best way to
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations promote higher levels of intake would be to increase the ingestion of high energy dense foods at night. DENSITY The energy density of a diet has been shown to markedly affect the total amount of food energy ingested. The greater the food energy content per gram of food consumed, the more total food energy ingested (Bell and Rolls, 2001; de Castro, 2004a; Yao and Roberts, 2001). We have shown that, for study participants consuming diets of varying energy densities during a seven-day period, the dietary energy density (calculated as the food energy content of the foods divided by their total weight) of meals is related to the total energy intakes from the meals; the dietary energy densities over the entire day are related to the total energy intakes over those same days; and the dietary energy densities of the participants’ diets are related to their total energy intakes. Dietary energy density is, to a large extent, positively correlated with intake, no matter whethermeals, daily intakes, or overall participant intakes were examined (Figure B-52). These findings resulted in the hypothesis that intake is not controlled on the basis of the energy content of the food, but rather on its volume, that is, the greater the food energy per unit volume of a meal, the more total food energy ingested. Dietary energy density is calculated as the food energy content of the foods divided by the total weight of those foods. The food energy component comprises the macronutrients, carbohydrate, fat, protein, and alcohol; the weight component comprises the weight of the macronutrients, nonnutritive solids, water contained in the foods, and drinks (water) ingested with the foods. By calculating separately the energy density from carbohydrate, fat, and protein, we investigated whether the components of food energy play different roles in determining the effects of dietary energy density on intake. Each of these densities was positively correlated with intake regardless of whether meals, daily intakes, or weekly intakes were studied (Figure B-53, left). When the carbohydrate, fat, and protein dietary densities were used as independent variables in a multiple regression prediction of energy intake, a variable outcome was produced depending on whether meals, daily intakes, or overall participant intakes were employed (Figure B-53, center). The one consistent outcome was that the dietary energy density of fat always had the strongest positive relationship with energy intake. When the overall dietary energy density was added to the regression, only overall dietary energy density had a strong positive relationship with intake, but all of the macronutrient relationships became negative with respect to intake (Figure B-53, right). This occurred regardless of whether meals, daily intakes, or overall participant intakes were used. The negative relationship suggests that when the overall energy density of a meal is considered, high densities of any macronutrient have a negative influence on intake. Further, this suggested that the overall dietary energy density is more important than the dietary energy density
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations FIGURE B-52 The relationship of dietary density and after meal stomach contents. Participants with a physical activity level of > 1.1. Mean estimated contents of the stomach at the end of meals of food energy (kcal) or volume (total grams) as a function of dietary energy density for meal (left), daily (center), and participant (right) intakes. SOURCE: Author’s unpublished data.
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations FIGURE B-53 Meal dietary density relationships with meal, daily, and participant intake. Mean univariate correlations (left), multiple regression β coefficients without (center) and with (right) inclusion of overall dietary energy density in the regression for the relationships of carbohydrate dietary energy density, fat dietary energy density, protein dietary energy density, and overall dietary energy density with meal (first bar of each set of three), daily (second bar), and participant (third bar) intakes. SOURCE: Author’s unpublished results.
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations of any particular macronutrient, implying that it is the meal dietary energy density per se that is the important influence on intake, not the meal’s components. The hypothesis that intake is controlled on the basis of the volume of food ingested infers that the volume of nutrients in the stomach at the end of the meal is the critical factor in determining intake. If the volume in the stomach at the end of the meal is relatively constant, then the food energy ingested would depend on the dietary energy density of the foods. The meal size is not an adequate estimate of the volume in the stomach because it does not include the nutrients from prior intake that still remain in the stomach. We attempted to test these predictions by estimating the contents of the stomach at the end of meals. Because the stomach empties in a very regular and predictable fashion (Hopkins, 1966; Hunt and Knox, 1968; Hunt and Stubbs, 1975), how much of the contents should have emptied over a given interval and how much should therefore be remaining at the time of a second meal is relatively simple to calculate (de Castro, 1987, 1999). Added to this model was an estimate of fluid movement into and out of the stomach according to the model of Toates (1978). Employing the reported intakes from the seven-day diary records along with these stomach emptying models, both the food energy (kcal) contents and the total gram contents of the stomach at the end of each meal were estimated and expressed as a function of the dietary energy density of the meal (Figure B-52, left). Although the food energy content of the stomach increased significantly with the increase in dietary energy density, the total volume (grams) of contents estimated to be in the stomach was not significantly dissimilar over the nine different dietary energy density levels. An analysis of the mean after-meal stomach contents over the entire day (on days that an individual participant had below- or above-the-mean dietary energy density) revealed a similar picture (Figure B-52, center). Again, food energy content of the stomach was high on the above-the-mean dietary energy density days, but the estimated weight of the contents of the stomach remained unchanged. Finally, the average estimated after-meal stomach contents of participants whose dietary energy densities differed were compared (Figure B-52, right). Exactly as was seen in the meal and daily intake analyses, higher stomach contents of food energy resulted in higher dietary energy densities, but there was no difference in weight of the contents. Using twin data, it was determined that the level of dietary energy density within the individual diets is affected by heredity (de Castro, 2004b). Additionally, the magnitude of the differences between the members of identical twin pairs in the density of their diet was positively related to the magnitude of the differences in the energy content of their daily intake (de Castro, 2004d). On the other hand, heredity did not seem to influence the relationship between density and intake. There were no significant heritable factors for either the correlation or the slope of the best fitting regression line between density and intake. Hence, it appears that heredity may influence the preferred dietary density that in turn
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations has a marked influence on intake. This infers that heredity does not cause individual differences in responsiveness to dietary density. SUMMARY The findings present a relatively clear picture of the roles of diurnal rhythms and dietary energy density in the control of short-term food intake. Intake in the morning appears to reduce overall intake, while intake at night appears to increase it. Dietary energy density, on the other hand, appears to be a major determinant of short-term food energy intake, with higher dietary energy density associated with substantially larger meals, daily intakes, and overall participant intakes. These results support the concept that short-term food intake is controlled on the basis of its weight and volume as opposed to its total food-energy content. This conclusion was supported by the observations that (a) overall dietary energy densities appear to be more important than the energy density of particular nutrients and (b) the estimated after-meal stomach contents appear to be constant regardless of the dietary energy density of the reported diet. These observations further suggest that short-term food regulation may occur on the basis of stomach filling. Based on these findings, the overall dietary density of assault rations should be maximized, and intake at night should be emphasized. The fact that time-of-day effects on intake appear to be heritable suggests that there may be considerable individual differences in response to manipulating this factor. On the other hand, the effects of dietary energy density on intake do not appear to be influenced by heredity, and this suggests that individual differences in response to dietary energy density manipulation should be minimal. Hence, to maximize intake in the field, maximize energy density and encourage night-time eating. REFERENCES Bell EA, Rolls BJ. 2001. Energy density of foods affects energy intake across multiple levels of fat content in lean and obese women. Am J Clin Nutr 73(6):1010–1018. de Castro JM. 1987. Macronutrient relationships with meal patterns and mood in the spontaneous feeding behavior of humans. Physiol Behav 39(5):561–569. de Castro JM. 1999. Inheritance of premeal stomach content influences on food intake in free living humans. Physiol Behav 66(2):223–232. de Castro JM. 2001. Heritability of diurnal changes in food intake in free-living humans. Nutrition 17(9):713–720. de Castro JM. 2004a. Dietary energy density is associated with increased intake in free-living humans. J Nutr 134(2):335–341. de Castro JM. 2004b. The control of eating behavior in free-living humans. In: Stricker EM, Woods, eds. Handbook of Behavioral Neurobiology. 2nd ed. Vol 14. Neurobiology of Food and Fluid Intake. New York: Plenum Press. Pp. 469–504. de Castro JM. 2004c. The time of day of food intake influences overall intake in humans. J Nutr 134(1):104–111.
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Nutrient Composition of Rations for Short-Term, High-Intensity Combat Operations de Castro JM. 2004d. When identical twins differ: An analysis of intrapair differences in the spontaneous eating behavior and attitudes of free-living monozygotic twins. Physiol Behav 82(4):733–739. de Castro JM, Plunkett S. 2002. A general model of intake regulation. Neurosci Biobehav Rev 26(5):581–595. de Castro JM, Bellisle F, Dalix AM. 2000. Palatability and intake relationships in free-living humans: Measurement and characterization in the French. Physiol Behav 68(3):271–277. Hopkins A. 1966. The pattern of gastric emptying: A new view of old results. J Physiol 182(1):144–149. Hunt JN, Knox MT. 1968. Regulation of gastric emptying. In: Coyle CF, Heidel W, eds. Handbook of Physiology. Vol 4. Alimentary Canal (Motility). Washington, DC: American Physiological Society. Pp. 1917–1935. Hunt JN, Stubbs DF. 1975. The volume and energy content of meals as determinants of gastric emptying. J Physiol 245(1):209–225. Toates FM. 1978. A physiological control theory of the hunger-thirst interaction. In: Booth DA, ed. Hunger Models: Computable Theory of Feeding Control. New York: Academic Press. Pp. 347–373. Yao M, Roberts SB. 2001. Dietary energy density and weight regulation. Nutr Rev 59(8):247–258.
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