The evolution of warfare strategies and the importance of maintaining the fitness of soldiers in military operations are the major driving forces behind the need to continually improve military rations. Also, the level of stress under military operations may affect food consumption in ways not seen to influence the food preferences of the general population. Because the factors that define the eating behavior of soldiers in these environments are still not well understood, ration designs need to be frequently reviewed and revised to adapt to both the soldiers’ needs and the demands of changing warfare scenarios. While an understanding of the reasons behind eating behavior observed in the field may be lacking, military rations, especially for soldiers in combat missions, need to be customized to address soldiers’ dietary needs and preferences in order to enhance intake. This report addresses those needs and preferences.
Chapter 1, Introduction, describes the committee’s task and the current concerns of the military regarding improvement of performance under combat, nutritional makeup of current rations for combat situations, and approaches taken to improve rations.
THE COMMITTEE’S TASK
The Department of Defense, through the US Army Research Institute for Environmental Medicine (USARIEM), asked the Institute of Medicine to appoint an ad hoc committee to conduct a study to determine the optimal nutrient content of a new combat ration. The ad hoc committee was to first review existing rations, their limitations for use during future force military deployments and combat operations, and the expected effects of combat operations on nutrient
status, health, and performance. The committee was then asked to recommend, within specific design constraints, the nutritional composition of a new ration designed for short-term use by soldiers during high-performance, stressful combat missions. The nutritional composition of this new ration would be optimized to best sustain physical and cognitive performance and to prevent possible adverse health consequences. This was to be done recognizing that the ration would likely have a hypocaloric energy content relative to daily expenditure in short-term assault situations—a limitation imposed by ration design and mission constraints. The committee was asked to focus on health issues of highest concern: dehydration, the gastrointestinal gut processes, and the function of the immune system. The committee was also directed to keep in mind the potential health and performance effects on the soldiers subsisting on this ration during its intended use in combat operations.
To address this task, the committee convened a workshop hosted by the USARIEM and the Natick Soldier Center (NSC) in Natick, Massachusetts, August 11–13, 2004, in which speakers addressed the issues brought to the committee by the USARIEM. The agenda is included in Appendix A. These presentations were the basis for the committee’s deliberations and recommendations and are included in this report as individually authored papers in Appendix B.
Ration Design Requirements
Among the chief design constraints of this daily ration as required by USARIEM are that it must fit within 0.12 cubic feet and weigh 3 lb (1.36 kg) or less. The ration is targeted for use by male soldiers who have an average body weight of 80 kg, approximately 16 percent body fat, are relatively fit, are within an age range of 18–45 years (average < 25 years), and who have no chronic metabolic disease but may be vulnerable to some common food allergies. During combat operations, the expected daily energy expenditure is 4,000–4,500 kcal/day, achieved through intermittent periods of high-energy expenditure (> 50 percent VO2max) mixed with longer periods of low-intensity movement and sustained for 20 hours per day. The soldier will rely on this ration during missions that last 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 a field-kitchen setting). The committee has designed this ration with the assumption that soldiers might be deployed to such missions repetitively for a maximum period of one month.
Specific Questions to Be Addressed
The committee task addressed the following four questions:
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 protein, fat, and carbohydrate for such an assault ration to enhance performance during combat missions?
What are the types and levels of macronutrients (e.g., complex versus simple carbohydrates, proteins with specific amino acid profiles, types of fat, etc.) that would optimize such an assault ration to enhance performance during combat missions?
What are the types and levels of micronutrients such as direct antioxidants (e.g., vitamins C and E, carotenoids), cofactors in antioxidant and other biochemical reactions with high metabolic flux (e.g., B vitamins, zinc, manganese, copper), or other bioactives (e.g., caffeine) that could be added to such rations to enhance performance during combat missions?
ORGANIZATION OF THE REPORT
The report is organized into an executive summary, chapters, and appendixes. The chapters include an introductory chapter and those chapters that directly answer the four questions that comprise the task of the committee above. Appendix B is composed of the written presentations of the workshop speakers; however, although they were the basis for the committee’s answers to the military’s questions, they should not be construed as necessarily representing the views of the committee.
This chapter provides some background information on current knowledge regarding the eating behaviors of soldiers under the physical and mental stress of high-intensity operations. The effects of high-intensity operations on performance as well as relevant ration development strategies are also discussed. Chapter 2 provides responses to the four specific questions posed to the committee. In addition, Chapter 2 provides a list of specific research needs for each nutrient that should be of interest to the military. Chapter 3 describes in detail the committee’s approach to establishing the levels and types of nutrients required, such as health considerations that were discussed in depth. It also includes a section on food matrix considerations that are critical for food developers who will design the rations. Chapter 3 concludes with a section on overall priority research needs.
The workshop agenda is presented in Appendix A. Appendix B includes the workshop presentations organized by topic: an introduction to information about combat rations; the role of carbohydrate, protein, and fat as fuel sources in performance and health enhancement or maintenance; the effects of micronutrients in performance and health enhancement or maintenance; approaches to improve the immune function and immune responses; prevention of kidney stones and of
impairments of gastrointestinal function; and food development considerations, such as strategies to develop food for individuals under stress and factors that may increase food consumption. Finally, the biographical sketches of the speakers and of the committee members are presented in Appendixes C and D, respectively. Appendix E contains a list of acronyms and Appendix F contains a glossary.
ENERGY EXPENDITURE AND FOOD CONSUMPTION DURING MILITARY OPERATIONS OR TRAINING
Data collected during field training indicate that with high energy expenditures of 4,000 kcal/day or more, soldiers tend to consume an average of 3,000 kcal/day, and even less when they depend on operational rations (i.e., rations designed for a wide variety of operations and settings but consumed for a limited period of time). In addition to the potential cognitive decrements due to a variety of stressors during short-term missions, underconsumption may result in a set of consequences ranging from body protein loss and fatigue to deficits in essential micronutrients that may impair physiological functions and result in performance decrements.
The wide range in total energy expenditures of various military groups and factors that appear to contribute to these differences have been described (Tharion et al., 2005). Studies in the field suggest that the typical energy intake of military personnel (soldiers, sailors, airmen, and marines) under a variety of scenarios and climatic conditions is approximately 2,400 kcal/day, even though energy expenditures of soldiers in combat units range from about 4,000–7,131 kcal/day depending on the level of physical activity and environment. Interestingly, these reports note that measured energy deficits for soldiers, whether they are in training school or in combat, were significant (Tharion et al., 2005).
Whereas this might seem normal for training situations due to restricted diets, the reasons for underconsumption during combat are complex, not well understood, and more difficult to avoid or counter. A Committee on Military Nutrition Research (CMNR) report (IOM, 1995) analyzed these reasons and provided recommendations to ameliorate them, focusing largely on the psychology behind eating behaviors during military activities. If the ration is designed to maintain health and performance, consumption of the entire ration (compared to selectively discarding food items) has the advantage of minimizing nutrient deficits resulting in potential adverse consequences in performance and health. Whether it is possible to do this in a combat situation remains to be determined.
IMPACT OF HIGHLY INTENSE OPERATIONS ON HEALTH AND PERFORMANCE
Physiological Consequences of Combat Operations
As mentioned in other parts of this report, during combat operations soldiers are often under energy deficit that can affect their health and performance. Several field studies have attempted to resolve the question of the minimum energy intake that will maintain military performance for a defined period of time by measuring either body weight loss or performance levels, or both. During the Ranger I and II studies (Moore et al., 1992; Shippee et al., 1994) soldiers completed an eight-week US Army Ranger training program under hypocaloric states and data on body composition, physical performance, cellular immune function, and medical problems were collected. In the first study, students were provided with a single meal of 1,300 kcal (Moore et al., 1992). In the second study (Shippee et al., 1994), an additional 200 kcal were provided in field exercises, which brought the total daily rations up to 1,570 kcal and 50 g of protein per day (IOM, 1992). During these two studies daily caloric deficits resulted in severe weight loss (> 10 percent), although the group that was provided additional calories and protein experienced less weight loss (12 percent versus 15 percent). Improvements in immune function were also seen with additional calories and protein. Both studies showed, however, that those severe hypocaloric states may result in harmful physical and cognitive effects to military personnel health (Moore et al., 1992; Shippee et al., 1994).
Evidence exists, however, showing that a body weight loss of less than 10 percent has no adverse consequences on health or military performance (Consolazio et al., 1979; Keys et al., 1950; Taylor et al., 1957). When rations that are specifically developed for short missions and that provide 2,000 kcal/day were tested, weight loss was around 3 percent of initial body weight. Although this weight loss does not present a major health concern, some measurements of performance were still impaired (Askew et al., 1986). In contrast, the same ration appeared to present no health concern when used with a carbohydrate supplement (Jones et al., 1990), even though the energy deficit was still high—approximately 2,000 kcal.
The loss of body weight as the main consequence of underfeeding during sustained operations (SUSOPS) results from reductions in both fat and lean body mass. Fat loss is an essential feature of starvation because body fat acts as an energy source when energy expenditure exceeds energy consumption. The reasons for protein loss, however, are not as well understood and such a loss of body protein could have adverse consequences for military performance. One of the first studies to illustrate that starvation causes body protein loss was the Minnesota starvation experiment (Keys et al., 1950). Recently, fat and lean tissue losses of 1.2 and 1.5 kg, respectively, were reported over a 72-hour SUSOPS (Nindl et al., 2002). Similarly, 38 percent of the ~12 kg body weight loss that
occurred during Ranger training (due to severe underfeeding) was attributable to nonfat tissue loss (Moore et al., 1992). A recent study conducted on the physiological and psychological effects of eating three different menus during 12 days of military training in a tropical environment (Booth et al., 2003) has been reported. Three groups of Australian Air Field Defense Guards received either freshly prepared foods, one combat ration pack (CRP), or half of a CRP, respectively, containing 3,600 kcal, 3,600 kcal, or 1,800 kcal. The menus were designed to provide a similar percent of energy from macronutrients as a percentage of total energy. There was substantial underconsumption in the CRP group versus the half-CRP group, which resulted in similar weight loss (about 1.7 and 2.6 percent, respectively), protein catabolism, and immune suppression in both of these groups; they also reported greater fatigue than the group eating fresh foods. Despite underconsumption, all groups ate sufficient protein to meet the military daily recommended intake for protein. It should be noted, however, that hypocaloric intakes raise protein requirements for maximal protein-sparing, and, therefore, the standard military daily recommended intake might not be sufficient.
Protein loss is one of the main consequences of combat operations and minimizing the protein loss might well be one strategy to maintain military performance. It has been suggested that this could be accomplished by a soldier storing an appropriate amount of body fat to be used during the mission, preventing severe body fat depletion, maintaining some level of physical activity, and increasing protein intake (see Hoffer, 2004 in Appendix B).
Other consequences of stress and underconsumption during combat likely include impairments in the immune and endocrine systems, dehydration, kidney stone formation, or gastrointestinal disturbances (see Montain, 2004 in Appendix B).
Impact of Combat Operations on Physical Performance
As described by Montain (see Montain, 2004 in Appendix B), performance of simple and well-learned motor tasks (e.g., weapon handling) do not appear to be compromised by sustained operational stress (Haslam, 1982). Endurance time, however, is frequently impaired during aerobic exercise tasks (VanHelder and Radomski, 1989), and there is an increased perception among subjects of the effort needed to perform the same task. Nindl and colleagues (2002) reported a 25 percent lower level of work productivity on a physical persistence task (building a wall for 25 minutes) when soldiers were fed a hypocaloric diet (a diet that contained > 50 percent less kilocalories than the soldiers’ energy expenditures) and allowed to sleep for only 1 hr/day over a four-day period as compared to the control. This is consistent with the hypothesis that SUSOPS compromise performance when tasks are prolonged and monotonous. Independent of energy intake (Rognum et al., 1986), operational effectiveness is also affected if sleep is inad-
equate. The sections below describe studies that show various factors affecting military performance.
Effects of Weight Loss and Energy Intake
Studies with prolonged operations lasting several weeks and associated with substantial losses of lean body mass (Moore et al., 1992; Shippee et al., 1994) have shown reductions in physical performance. The caloric deficit and weight loss associated with SUSOPS scenarios, however, appear to have inconsistent effects on soldier performance (Montain and Young, 2003). One of the difficulties with these studies is that physical performance is measured with a variety of tests that may or may not be reliable or indicative of work productivity. In addition, confounding factors, such as small sample sizes, lead to scores that were improved with time. Generally, earlier studies of short-term duration suggest that several days of underfeeding have limited ill effect on muscle strength and aerobic endurance; however, physical performance also depends on the degree of energy deficit and length of the mission.
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 Radomski, 1989). In the study described above (Booth et al., 2003), no differences were evident among the three groups in the areas of physical fitness (as tested by chin-ups or sit-ups and running times), daily activity, sleeping quality, or cognitive function, despite a weight loss of approximately 3 percent reported in the groups on the CRP diets. The authors concluded that a 3 percent weight loss after 12 days was unlikely to be detrimental to military performance, and the loss of protein was not considered significant.
The lack of performance decrements with short-term operations, however, is not universal (Legg and Patton, 1987). A SUSOPS scenario lasting less than one week resulted in reduced maximal aerobic power and endurance (Guezennec et al., 1994), as have sleep-deprivation studies (Van HElder and Raomski, 1989).
Earlier studies suggested that if mineral supplements were included in the ration, health and performance may be maintained over a short period of time (10 days) (Consolazio et al., 1967a, b). In this case, however, performance was measured as handgrip strength, which might not be a good measurement of military performance. No differences, either in time to complete an assault course or in prone marksmanship performance, were reported when cadet soldiers were provided 1,500 or 8,000 kcal/day during a five-day scenario (Rognum et al., 1986). In another study, an 8 percent reduction in maximal aerobic power was noted when soldiers were restricted to 1,800 kcal/day, but no reductions were apparent when soldiers were fed 3,200 or 4,200 kcal/day (Guezennec et al., 1994). Similarly, reductions in shot group tightness on a marksmanship task were reported after sustained road marching during which soldiers were fed
250 g/day of carbohydrate, but no change was noted when soldiers consumed a daily diet with 400 or 550 g of carbohydrate (Tharion and Moore, 1993). Military performance, measured by aerobic performance, psychomotor and vigilance tasks, and military performance test scores, were no different for subjects on a hypocaloric diet (2,400 kcal/day) versus those on eucaloric diets for 7 to 10 days while energy expenditures were 3,800 kcal/day (Rai et al., 1983).
Most of these studies, however, were not conducted under the stressful circumstances of actual combat, which might alter the results. As has been noted by others (Montain and Young, 2003), despite confounding factors, the data available suggest that moderate levels of weight loss have limited ill effects on the ability of the soldier to perform tests of accuracy and coordination, anaerobic power, and endurance.
Effects of Eating Schedule and Nutrient Intake
Time of ingestion and content of the previous meal may be an explanation for the divergent results described above regarding the effects of varying energy intake on performance. A study found a relationship in that an increase in energy (or carbohydrate) intake sustains uphill run time over three days of physically demanding field training (Montain et al., 1997). Moreover, when provided with the same amounts of carbohydrate and energy, soldiers who best sustained their uphill run time performance had eaten carbohydrate during the four hours preceding the uphill run, while soldiers with the greatest decrement had eaten none of their rations since the previous night’s meal. The results of this study suggest that soldiers subsisting on diets at these energy and carbohydrate levels during high-paced operations are receiving nearly the minimum level of energy needed to sustain performance, necessitating good food discipline (i.e., eating the food provided) or acceptable food choices (i.e., eating the carbohydrate-containing foods), or both, to preserve physical performance.
Effects of Sleep Deprivation
According to recent surveys conducted in the field during combat missions, some soldiers sleep an average of 4 hr/day; most of them, however, sleep 5–6 hr/day (personal communication, C. Koenig, USARIEM, November 15, 2004). Current military doctrine requires that units operate around the clock during times of conflict because the success of battlefield operations depends, at least in part, on maintaining the momentum of continuous day–night operations (US Department of the Army, 1997), especially with the technological advances that have enhanced night-fighting capabilities.
A recent CMNR report reviewed the consequences of sleep deprivation on military personnel (IOM, 2004b). It was noted that depriving humans of proper
restorative sleep produces attention lapses and slower reaction times, which are associated with poor performance (Krueger, 1991). Sleep-deprived personnel lost approximately 25 percent of their ability to perform useful mental work with each 24-hour period of sleep loss (Belenky et al., 1994). The CMNR report also noted that, by the end of three days without sleep, combat service members may be considered totally ineffective in the operational setting, especially if they are performing complex tasks such as operating computerized command-and-control centers. Although under SUSOPS this is not the usual sleep interval, decreases in cognitive function may still be expected given that assault operations providing little time to sleep can last up to a month.
Over the past several years, the problem of sleep loss and fatigue has escalated due to the increased requirements on military forces caused by reductions in manpower and other resources (IOM, 2004b). The efficiency of combatants in SUSOPS can be significantly compromised by inadequate sleep (Krueger, 1991). Vigilance and attention suffer, reaction time is impaired, mood declines, and some personnel begin to experience perceptual disturbances. Cognitive abilities suffer a 30 percent reduction after only one night without sleep, and a 60 percent reduction after a second sleepless night (Angus and Heslegrave, 1985). In this way, marksmanship can be compromised by sustained operation activities. Significantly impaired marksmanship occurred after 73–74 hr of total sleep deprivation during Navy Seal training (Tharion et al., 1997). Specifically, there was a greater distance from the center of mass (by 20 percent) as well as increased dispersion of shot groups, both indicative of reduced marksmanship. These adverse findings occurred despite a 50 percent slower sighting time. In contrast, no negative results were observed during nine days of SUSOPS (which allowed two days of no sleep and four hours of sleep for the seven remaining days) on shot group clustering when troops fired in the prone supported position (Haslam, 1982). The ability to acquire and accurately hit a randomly appearing target, however, declined progressively during the first two days of the study and was 10 percent below baseline performance (only 5 hits versus 6 of 9 hits) after nine days. SUSOPS duration may be a factor. Despite soldiers’ rating of the marksmanship task as more difficult to perform after 48 and 72 hours of SUSOPS, in another study there was no reduction in the number of randomly appearing targets hit during the test (Johnson et al., 2001). When task durations extend beyond 15 to 20 minutes, performance deteriorations from fatigue become far more pronounced than when the task durations are shorter (Caldwell and Ramspott, 1998; Wilkinson, 1969; Wilkinson et al., 1966).
Although not all types of performance are affected to the same degree by sleep loss, the fatigue from prolonged duty periods clearly jeopardizes unit readiness in the operational context. This is especially the case for tasks that are lengthy, devoid of performance feedback, or boring.
DEVELOPMENT OF RATIONS FOR MILITARY OPERATIONS
Improvement of Rations Throughout Time
Since the Civil War, and especially after the end of World War II, the US military has devoted a great deal of effort to develop and improve the existing rations for soldiers both in combat and in garrison. The military recognized that, rather than simply providing a nutritionally balanced diet, rations needed to be targeted to the specific situation in which military personnel operate. The environment (i.e., geographical location and climate) was recognized as an important factor that influenced ration development; changes in warfare tactics have also resulted in new dietary needs and consumption habits. For example, nutrient requirements for extended operations in temperate climates might not be the same as those for short-term extreme conditions during which sweating might be severe and physical activity strenuous. In 1947 (US Department of the Army, 1947), the military had recognized the importance of maintaining personnel performance as well as the need to provide acceptable foods to adequately maintain their stability and nutritional needs.
Throughout the ensuing years, many types of rations have been and continue to be developed to provide for the nutritional needs of soldiers in specific situations. As components of the Department of Defense, (1) Combat Feeding Directorate (CFD), Research, Development and Engineering Command, NSC, and (2) the Operational Ration Business Unit of the Defense Supply Center, Philadelphia’s Directorate of Subsistence, collaborate to develop, test, evaluate, procure, and support all military rations. In developing the rations, food technologists at the CFD collaborate with nutritionists and physiologists at USARIEM, which has the responsibility of setting the nutrient composition of the rations in compliance with nutrition standards established by the Surgeon General of the US Army (US Departments of Army, Navy, and Air Force, 2001). The nutritional standards for rations have evolved as knowledge about human nutrient requirements has expanded. The Military Dietary Reference Intakes (MDRIs) are quantitative reference values for nutrient intakes to be used for planning and assessing diets for the healthy military population.
Operational and restricted rations are designed for military personnel in a wide variety of operations and settings to be used during limited periods of time. “Operational” rations are designed to be nutritionally adequate, whereas “restricted” rations are incomplete and used for shorter periods of time. See Table 1-1 for a comparison of nutrient reference values and energy levels for military rations and for the general population (Dietary Reference Intakes or DRIs). MDRIs are mostly based on the DRIs, with some modifications that consider the special needs of military personnel.
Increasing the food intake of soldiers during times of high energy expenditure has been a constant challenge for those responsible for developing military
TABLE 1-1 Military Recommended Intakes for Men in Garrison Feeding, Operational and Restricted Rations Compared to Recommended Intakes for the General Population, Men 19–30 Years of Age
rations. As mentioned in other parts of this report, palatability is a critical factor that greatly determines energy intake by soldiers. To adapt the ration items to the wants and needs of the soldier, an important aspect of ration development is the information gathered from surveys in the field regarding soldiers’ food preferences, their acceptance of rations, and their resultant behavior. For example, Meals, Ready-to-Eat (MREs), which are rations to sustain soldiers for no more than 10 days and in the absence of food service, have been improved since their introduction in 1993 as a result of survey findings. The MREs’ menus have increased from 12 to 24 varieties and now include four vegetarian meals and 150 new items.
One of the surveys (unpublished data) was conducted with soldiers stationed at Ft. Drum, New York, during a 10-day field training exercise in 1996; the study tested the acceptability of a new MRE developed as a result of prior studies that concluded preferences for larger serving sizes and more variety in menus. This study revealed that an increased number of fruits and snacks were favored and that a decrease in total calories would be desirable.
Another study with the 28th Combat Support Hospital personnel assessed a test ration in comparison to that year’s version of the MRE during energy expenditures averaging 4,000 kcal/day for 11 days (Baker-Fulco et al., 2002). The test ration contained new items and more carbohydrate and less fat than the control MRE. Subjects increased energy intake as intended but changes in protein intake were marginal with the test ration. For both rations, underconsumption resulted in most subjects not meeting the military recommended intakes for a number of nutrients. This study showed that manipulation of the food items and of the distribution of macronutrients in the ration could reduce energy deficits in military personnel. Studies such as these are critical to determine the food preferences and the eating behavior of soldiers, such as which items are discarded or eaten more frequently, in specific situations. Improvements in the MRE and research efforts in food technology have been described in an earlier CMNR report (IOM, 1995).
Current Efforts to Improve Rations
Although MREs are envisioned as rations to sustain soldiers in the absence of food service facilities of field kitchens (as in the case of SUSOPS), MREs are designed for use for periods of no more than 10 days, at which time field kitchens or other facilities are to be made available. As the number of SUSOPS has increased in recent years, the need to reevaluate existing ration designs and develop a new lightweight ration specifically to meet the metabolic needs of soldiers during SUSOPS (e.g., three- to seven-day operations) is a high priority. MREs are not suitable for these operations because of the weight they add to the already heavy loads that soldiers carry when no resupply is planned. When MREs were provided for SUSOPS, anecdotal evidence revealed that, in an attempt to
lighten the loads, soldiers selectively discarded food items; this practice has become a widespread problem and may result in unbalanced diets that could possibly jeopardize a soldier’s health or performance or both during an assault operation.
With these issues in mind, new assault ration prototypes have been under development by USARIEM and the NSC. The current concept is a lightweight ration to be eaten “on the go” that, unlike the MREs, requires no preparation. Items in the current prototype ration include fruit bars, dried fruit, meat pockets, a dairy bar, and beef jerky. The acceptability of these prototype food items has been tested in the laboratory and in garrison situations, and the results to date are promising (personal communication, A. Young, USARIEM, August 11, 2004). Although it is appropriate to initially conduct such tests, testing under the unique circumstances of a combat situation is a critical step to confirm acceptability and revisit the ration design if poorly accepted. Currently, these rations are being tested in the field, and results from those tests, as well as the recommendations in this report, are expected to help military food developers and nutritionists optimize the utility of the assault ration.
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