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Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
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1
Introduction and Background

Not Eating Enough, 1995

Pp. 3–40. Washington, D.C.

National Academy Press

The Committee on Military Nutrition Research (CMNR) has reviewed many studies over the past 10 years that evaluated the acceptance and intake of military food items as part of its continuing task of assessing the nutritional adequacy of military operational rations (see IOM, 1992a for summary). The current main operational ration, the Meal, Ready-to-Eat (MRE), was developed in 1981 as the primary ration to replace the C Ration, which had been the mainstay of operational rations for many years. The MRE is compact, has a long shelf life, and can be issued directly to the individual soldier. It can be eaten with or without heating, and the 3,600 kcal provided by the total ration was designed to meet the Military Recommended Dietary Allowances (MRDAs) (see AR 40-25, 1985) for all nutrients. The MRE was initially developed for use up to 3 days at the start of military operations until other field feeding systems became available. The simplicity of this system, logistically and in terms of reduced need for food preparation personnel, led to the desire to use this ration for extended periods of time (i.e., 10 to 30 days). Field testing was thus ordered to evaluate the effectiveness of the MRE over extended periods of time. Summaries of these field studies can be found in Chapters 6 through 10 of this volume.

The CMNR reviewed many of these studies when they were initially completed and noticed that underconsumption of the ration appeared to be a

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

consistent problem. Typically, soldiers did not consume sufficient calories to meet energy expenditure and consequently lost body weight. The energy deficit has been in the range of 700 to 1,000 kcal/d and thus raises concern about the influence of such a deficit on physical and cognitive performance, particularly over a period of extended use. Anecdotal reports from Operation Desert Storm, for example, indicated that some units may have used MREs as their sole source of food for 50 to 60 days—far longer than the original intent when the MRE was initially field tested. In contrast, studies with special purpose subsistence rations that supplied limited energy (1,500–2,000 kcal), but were based on similar design of the MRE, reported that the rations were fully consumed, and soldier weight losses were experienced as would be predicted by the limited calories in the rations. Systematic records of personnel weight loss and nutritional status were not maintained during the combat situation of Desert Storm. There were, however, no apparent major nutritional problems associated with this long-term use of MREs. Based on continuing research with the MREs as described later in this chapter and in Chapters 6 through 10 of this report, the Army Surgeon General, with concurrence from the Air Force, Marine Corps, and Navy, has recently issued a revised policy statement that ''…allows the MREs to be consumed as the sole source of subsistence for up to twenty-one days" (U.S. Department of the Army, 1995).

There have been successive modifications of the MRE since 1981. These modifications in type of food items, diversity of meals, packaging, and food quality have produced small improvements in total consumption but have not significantly reduced the energy deficit that occurs when MREs are consumed. This problem continues in spite of positive hedonic ratings of the MRE ration items in laboratory and field tests. The suboptimal intake of operational rations thus remains a major issue that needs to be evaluated.

This report originated from a concern within the military about the consistency of the deficit in energy intake and whether such a decrement could lead to meaningful reductions in physical and/or cognitive performance of troops during military operations. The report focuses on the various factors that may contribute to the reduced intake of operational rations, the potential effect on soldier performance, and suggested steps that may be taken to overcome the problem. The data covered in this report are limited to controlled field studies of operational rations. The information and conclusions drawn from these data, while reflecting the military performance demands in rigorous field conditions and environmental extremes, do not, however, reflect the extreme physical, social, and psychological stress of combat.

THE COMMITTEE'S TASK

The CMNR of the Food and Nutrition Board (FNB), Institute of Medicine, National Academy of Sciences, was asked to assist in a collaborative program

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
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between scientists in the Military Nutrition Division, U.S. Army Research Institute of Environmental Medicine (USARIEM), and the U.S. Army Natick Research, Development and Engineering Center (NRDEC) to strategies on how to overcome underconsumption of military operational rations. The CMNR's task was to review the data on ration intake in controlled field settings, to determine whether the consistently reported suboptimal energy intake could be termed underconsumption , to evaluate whether this lowered intake could be detrimental to performance, and to discuss strategies that might be effective for increasing ration consumption. The committee was thus charged with reviewing the existing data on ration intake from studies that had been conducted by the Army and integrating current scientific hypothesis with relevant data on factors that depress or, conversely, enhance food intake. Other than anecdotal information, data were not presented on ration intake from soldiers engaged in combat situations.

The committee was also asked to address five questions that dealt with the concept of underconsumption as it related to military applications. These questions are listed in Table 1-1.

The basic factors and viewpoints of key scientists from USARIEM and NRDEC related to soldier underconsumption were initially discussed with the chair and several members of the CMNR in a small planning session in March, 1993. At this meeting the CMNR indicated their recognition of the complexity of the issues and decided to convene a workshop that would provide more specific information about the military research coupled with relevant presentations from scientists from academic and industry settings. In particular the committee members indicated the workshop scope should include more specific information about (1) Army field feeding logistics; (2) new developments

TABLE 1-1 Questions to be Addressed in This Report

1. Why do soldiers underconsume (not meet energy expenditure needs) in field operations?

2. What factors influence underconsumption in field operations? Identify the relative importance of

• rations,

• environment,

• eating situation, and

• the individual.

3. At what level of underconsumption is there a negative impact on physical or cognitive performance?

4. Given the environment of military operations, what steps are suggested to enhance ration consumption? To overcome deficits in food intake? To overcome any degradation in physical or cognitive performance?

5. What further research needs to be done in these areas?

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
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in operational rations; (3) an overview of Army research on food intake patterns and factors affecting food intake; (4) recent Army research results on the impact of lowered energy intake on performance; and (5) expert reviews of physiological, psychological, and social factors that influence eating.

The workshop therefore was convened on November 3–4, 1993 to assist the CMNR in responding to the Army and provide background information useful for developing its report. This workshop included presentations from military and nonmilitary scientists with expertise in food engineering, food marketing strategies, food science, nutrition, nutritional biochemistry, physiology, psychology, and social factors. A panel discussion was held at the end of the workshop to summarize the findings and discuss potential strategies to increase ration intake. The four invited panelists contributed their expertise in complex data analysis, food development, ingestive behavior, and nutrition education. The panel discussion, summary statements, and recommendations were important contributions to the committee deliberations and conclusions. The invited speakers discussed their presentations with committee members at the workshop and submitted the contents of their verbal presentations as written reports. The committee met after the workshop to discuss the issues raised and the information provided. The CMNR later reviewed the written reports and drew on its collective expertise and the scientific literature to develop the summary, conclusions, and recommendations that appear here and in Chapter 2.

Terms Used in This Report

The term underconsumption will be used in Part I of this report to represent food intake that has been documented to provide fewer calories than required by energy expenditure on an individual or group basis. Use of the term underconsumption in this manner thereby assumes a longer-term risk of undernutrition if it persists over an extended period of time.

In the military sense, a ration is the nutritionally adequate food allotment for one person for one day; a military operational meal is a unit making up one-third of the daily nutritional requirement of a ration. An operational ration is a collective term for rations used in the field or in combat. For operational rations the choice of a specific ration or meal type for individual or group feeding is determined by the tactical and logistical characteristics of the feeding situation, or Mission, Enemy, Troops, Terrain, and Time (METT-T) dependent (Mason et al., 1982; NLABS, 1983). Throughout Part I the committee uses the term ration collectively to represent the five types of current military operational rations (Meal, Ready-to-Eat [MRE], T, B, and A Rations, and the Unitized Group Ration [UGR]). The ration types are described

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

briefly here and in detail by Gerald A. Darsch and Philip Brandler in Chapter 7.

The Meal, Ready-to-Eat (MRE) is an operational ration currently configured as 12 menus with all 12 menus packaged together in a case. Each meal weighs 11/2 pounds (0.7 kg) and comprises six to eight components. The individual meal is packaged in retort1 pouches, and entrees include chicken stew, pork with rice, and spaghetti, with accompaniments of fruit, cookies, cheese crackers, a beverage, and seasonings. Individual meals are nutritionally balanced in accordance with the Office of the Surgeon General's (OTSG) requirements as stated in U.S. Army Regulation 40-25 (1985). The MRE is a general purpose ration that is intended to be carried and consumed in the field in conflict situations where cooks cannot prepare group meals by virtue of the tactical environment. Since 1983, the MREs have been improved continually based on surveys of troop feedback from the field, including early feedback from Operation Desert Shield/Storm; from focus groups; and from individual interviews with soldiers.

The Tray Ration (T Ration) is composed of heat-and-serve prepared foods in half-size steam-table (1.66 cubic ft) metal containers, with all necessary components, including napkins, knives, forks, trays, and so on, contained in modules. Each meal is nutritionally balanced in accordance with Army Regulation 40-25 (1985) and includes an entree, a vegetable, a starch, and a dessert. The T Ration provides a 10-d breakfast and a 10-d lunch-dinner menu for 18 military personnel. The most tactically versatile of the group rations, the T Ration provides hot group meals with limited personnel and minimal equipment. The T Ration has been the subject of a product improvement program at NRDEC, and menus have been restructured on a continuous basis to eliminate less acceptable items and to add new, more highly acceptable items.

The B Ration is a cook-prepared group meal that requires a field kitchen. All ingredients used to prepare the B Ration are semi-perishable, and therefore, no refrigeration is required. Most of these semi-perishable ingredients are standard institutional-type ingredients such as flour, sugar, and large (# 10) cans of vegetables and meats. In addition, there are 13 unique items that are either dehydrated or chunked and formed. Preparation of these meals in the field using field kitchens is a demanding task that requires considerable culinary skill. The B Ration provides a 10-d breakfast and dinner menu.

The A Ration is a meal prepared by cooks in a field kitchen where refrigeration is available, and chilled and frozen products can be provided.

1  

In retort processing, packaged foods are heat treated (at approximately 250¹F) under pressure for sufficient time to inactivate food microorganisms. Examples of foods that require retort processing include low acid foods with sufficient moisture to support the growth of microorganisms (e.g., entrees, vegetables, starches, and desserts).

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

Like the B Ration, this meal requires considerable cooking skill and demands careful inventory management because of both the perishable nature of some ingredients and the total number and quantity of ingredients necessary to prepare and serve meals. The A Ration provides a 10-d breakfast and dinner menu.

The Unitized Group Ration (UGR) integrates into a unified system the A Ration minus the perishables, the B Ration, the T Ration, and additional brand-name items that can be quickly prepared. The UGR contains 15 breakfast menu options (5 each of rations A, B, and T) and 30 lunch-dinner menu options (10 each of rations A, B, and T). Each of the meal options is unitized in six containers and provides all of the ingredients, trays, utensils, napkins, condiments, and so on, necessary to feed 100 military personnel. The six containers make up one layer of a pallet, and four layers constitute a pallet load. This system maximizes the efficiency of group feeding in the field and reduces the number of line items a cook must order for a meal to one-tenth the number formerly required. The UGR has been developed recently and is currently under final review.

Definition of the Problem and Report Organization

To develop answers to the questions posed by the Army, the CMNR sought to identify the magnitude of the lowered consumption experienced by troops in field settings, whether and when the energy deficit affected performance of militarily relevant tasks, and the specific factors involved. In this chapter, initially the committee reviewed the research evidence related to underconsumption and performance. In addressing the data with the assistance of personnel from USARIEM and NRDEC, the committee determined that the situational factors of the eating environment and attributes of the food were the major elements involved in reduced consumption. A review of research findings in these general areas is then presented in the sections that follow with an overview of newly proposed plans for changes of military operational rations and field feeding programs. The CMNR concludes its research synopsis with a discussion of the potential impact of these proposed changes on the underconsumption problem and incorporates a discussion of alternative research and operational strategies suggested at the workshop.

LOWERED INTAKE AND PERFORMANCE

Overview of Energy Intakes During Military Exercise

Problems of suboptimal consumption during military exercise in real-life situations have been studied by the Military Nutrition Division at USARIEM

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

(see Baker-Fulco, Chapter 8 in this volume). Either food records or, for group feeding situations, visual estimation techniques are used to estimate soldier intakes for from 5 to 30 days. Preweighed or prepackaged rations are used for much of the food in the field. Studies have been done of military groups in garrison dining facilities in normal and training environments to obtain comparative data on energy intake. See Table 1-2 for a summary.

Typical energy intakes of military men in garrison situations range from 2,730 to 3,260 kcal/d. When soldiers are actively involved in training, garrison intakes range from 3,200 to 4,650 kcal/d. In field training operations male soldiers had significantly lower intakes, ranging from 2,265 kcal in a study in Bolivia where the MRE and B Rations were fed to individuals in a high-altitude environment (Edwards et al., 1991), to a high of 3,713 kcal at Fort Sill where A Rations were provided three times a day in the field as hot meals at regularly scheduled times (Rose and Carlson, 1986). The Fort Sill study was considered to represent the optimal situation for feeding soldiers in field operations. In another study at Fort Chaffee, a control group received hot meals in a fixed dining facility while the MRE group received the rations in their barracks at scheduled meal times in a thermally neutral environment (C. D. Thomas et al., U.S. Army Research Institute of Environmental Medicine, Natick, Mass., unpublished data). There was weight loss in both groups, but the MRE group lost twice as much weight over 30 days (4.8 percent of body weight versus 2.4 percent in the control group), with a difference in energy intake of about 400 kcal/d. These estimates of deficits have been confirmed in studies of energy expenditure in the field using the doubly labeled water technique, which show a typical daily deficit of 500 to 2,000 kcal (see Chapters 8 and 14).

In a recent study of women in a hot environment at Fort Hood, Texas, that provided two B Rations and one MRE per day, the average intake was 2,343 kcal/d, which is close to the MRDA of 2,400 kcal (Rose, 1989). The women in this study maintained their body weight; however, they had liberal access to commercial snack foods. In previous studies in garrison during training, women had similar intakes ranging from 2,314 to 2,592 kcal/d, as compared to nontraining garrison intakes of 1,832 kcal/d (see Baker-Fulco, Chapter 8 in this volume for summary). In the Bolivia study mentioned above (Edwards et al., 1991), the women demonstrated a marked decrease in intake similar to that seen in men at high altitudes with an average intake of only 1,668 kcal/d.

In studies conducted in cold weather, energy intakes are found to be much higher, demonstrating the effect of the increased energy requirement in cold-weather exercises. However, the increased level of intake does not offset the increased level of expenditure, as verified by studies conducted in the cold in which doubly labeled water was used to estimate actual energy expenditure (see Baker-Fulco, Chapter 8 in this volume).

Many contributing factors such as the ration itself, meal schedules, environment, military and unit command emphasis, military feeding policy,

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

and individual biological rhythms may be important contributors to underconsumption. Food waste in the field is considerable, with 1,000 to 3,000 kcal/d differences occurring when actual intake of rations is monitored (only 51–78 percent of the ration being eaten). Soldiers, if given the opportunity, throw out foods they do not like (cf., Rose, 1989; Baker-Fulco, Chapter 8 in this volume). Also, there are time constraints that may prevent heating and preparing the rations. There appears to be a fatalistic attitude on the part of commanders and troops about the weight loss, which additionally may contribute to underconsumption and often deliberate dieting (see Baker-Fulco, Chapter 8 in this volume).

In summary, energy intake of men and women decreases in the field compared to the garrison during training. In the MRE field studies using doubly labeled water, there appears to be an energy deficit of 500 to 2,000 kcal/d and resultant weight loss for the study participants. When men and women trainees were given the opportunity to augment their rations with snack food or when regularly scheduled hot meals were provided, body weight was maintained.

Effects of Ration Modifications in Energy Intake, Weight Change, and Food Acceptance

Five studies that compared the original MRE with improved versions containing 15 to 51 percent substitutions of new food items (see Hirsch, Chapter 9 in this volume) increased the ratings of soldier acceptability. However, increases in acceptability were only accompanied by increases in energy intake in four of the five studies. In other studies with improved T Rations, although there was an increase in acceptance, there was no increase in energy intake. These results must be viewed with caution as the limited increase in consumption might be due to the introduction of dietary variety (Rolls and Hetherington, 1989) or to the novelty effect of these new, highly palatable foods. These data thus raise an additional research question of whether heightened acceptance ratings and increased consumption might decline with repeated exposure to these new food items. Edward Hirsch (see Chapter 9 in this volume) has suggested that monotony is likely to set in; however, studies have not been conducted to address this issue.

In addition, food acceptance as measured by hedonic ratings represents only one aspect of a complex issue. Certain foods such as bread, high starch-containing vegetables, and milk, which typically receive only average hedonic ratings, will continue to be consumed in quantity when other more highly rated foods will be rejected as no longer palatable (see further discussion later in this chapter and in Chapters 11 and 13). A broader range of foods and menus with increased variety may need to be considered. There are 18 MREs now proposed, but the effect of this variety of menus on intake needs to be tested

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

over a period of time. In addition, carefully designed menu rotation studies that incorporate current understanding of the impact of variety, sensory specific satiety, temporal habituation patterns, energy density, the fat and fiber content of foods, and palatability on intake and body weight would provide directly relevant information (cf., Jordan et al., 1981; Kissileff, 1984; Levine and Billington, 1994; Porikos et al., 1977, 1982; Prewitt et al., 1991; Rolls, 1986; Rolls and Hetherington, 1989; Rolls et al., 1981, 1992).

In summary, the problem of underconsumption from the perspective of those scientists involved with the food development and testing aspect of rations is that, despite significant efforts to test operational rations and measure their acceptability in the field over the last 10 years, there continues to be generalized weight loss when compared to garrison feeding studies even with the same MRE rations (Hirsch and Kramer, 1993; see Table 1-2). Thus, any review of the problem must include situational factors, such as environment, social settings, logistics, and temporal considerations, as well as perceptions or image of ration acceptability, and the possible interactions of all of these on consumption behavior.

When Does Soldier Physical Performance Decline as a Result of Lowered Consumption?

True underconsumption of food, in the face of continuing or increased expenditures of body energy stores, leads to weight loss. A loss of body weight, over time, thus appears to be the easiest guide for quantifying dietary underconsumption. However, for an accurate evaluation of weight loss data, it is important to know the changes in body composition that account for the lost weight.

As discussed in previous CMNR reports (IOM, 1992a, 1993), different combinations in the complex relationships between dietary intake and energy expenditure can result in widely different forms of weight loss. As examples:

  • Initially, simple starvation produces primarily losses of fluids, electrolytes, and small amounts of lean body mass and body fat, but then the body begins to derive virtually all of its energy needs from its fat stores, while using every possible metabolic method to conserve body nitrogen.

  • Weight losses due to acute disease or trauma are associated initially with predominant losses of body muscle mass because of the acute phase reaction. This loss of muscle mass may be accompanied by losses in water, electrolytes, and fat.

  • Weight losses associated with extreme energy expenditures during periods of food restriction (such as in U.S. Army Ranger training [Moore et al., 1992; Shippee et al., 1994]) are associated with losses of body fat, as well as with losses of body water and muscle mass.

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
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  • Abrupt weight losses (within 24–48 hours) associated with high energy expenditures in hot, humid environments or protective clothing are due mainly to acute losses of body fluid and electrolytes.

In assessing the degree of weight loss needed to induce measurable decrements in physical performance, Karl E. Friedl (see Chapter 14 in this volume; see also Table 1-2) reviewed data from a number of historical situations and studies, as well as data recently generated in separate studies of Scandinavian and U.S. Army Ranger trainees. There were some similar, overall conclusions that could be drawn from these diverse studies and weight loss situations: decrements in physical performance were not evident with minor degrees of weight loss or losses primarily of body fat.

In studies conducted at the U.S. Army Ranger Training School (see Chapter 14 in this volume), decrements in physical performance occurred when weight losses of 10 to 15 percent were recorded over the 6 to 8 weeks of this intensive training program. Data from these studies cannot be directly applied to other military situations because Rangers in training in the Ranger School are highly motivated, thus these results may not be indicative of what can be expected from regular military units. The rate of weight loss in this situation must be taken into consideration. Weight losses of as little as 3 to 5 percent in 24 to 48 hours or less are primarily due to dehydration and will result in reductions in performance (see for example Altman and Fisher, 1986). Weight losses of 6 to 10 percent in a similar time period are potentially debilitating and may adversely affect the health of individuals. Therefore, when evaluating the effects of underconsumption of operational rations and resulting weight loss, it is necessary to eliminate dehydration as a factor and be concerned with well-hydrated individuals in assessing the effect of weight loss on performance.

The rate of weight loss is also an important consideration in healthy and adequately hydrated individuals and is primarily related to the energy deficit. An approximate calculation is that a deficit of 3,500 calories equates to 1 lb of weight loss in overweight individuals. Therefore, extreme rates of weight loss in the presence of adequate hydration are indicative of severe underconsumption. A soldier of 160 lb body weight losing 10 percent of body weight or 16 lb in 2 weeks (14 days) would be experiencing a calorie deficit of approximately 16 x 3,500 divided by 14, or approximately 4,000 kcal/d. A similar loss in 4 weeks (28 days) represents an approximate daily deficit of 2,000 kcal/d; 8 weeks (56 days), 1,000 kcal/d deficit; and over 16 weeks (112 days), a 500 kcal/d deficit. Physically fit soldiers with less body fat than the usual, somewhat overweight individual would experience less fat loss and more reduction in lean body mass as weight loss progresses (see discussion in Altman and Fisher, 1988; Vanderveen et al., 1977). Therefore, the fit soldier is likely to have a reduction in performance capability related to the reduction in lean body mass similar to the studies with lean Gambian laborers, where

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

changes in body weight were mirrored by changes in fat-free mass, and fat-free mass was significantly correlated with physical work performance (Diaz et al., 1991). Workers in less developed countries where energy deficits are common during certain seasons voluntarily reduce their physical activity to compensate for the reduced energy intake and thus help retain lean body mass (Scrimshaw and Young, 1989).

There is the suggestion from the data on Ranger Training School (Moore et al., 1992; Shippee et al., 1994; see Chapter 14 in this volume) that body weight loss of less than 10 percent in hydrated individuals may not significantly reduce physical performance. However, concern arises with continued energy deficits that may occur if troops are redeployed after losing 5 to 10 percent of their body weight and before having an opportunity to regain this lost weight. If inadequate energy intake continues and further weight loss occurs, performance deficits can be expected. In addition, voluntary physical activity will likely be reduced, and situations that demand high energy output may result in reduced ability to perform (Scrimshaw and Young, 1989).

A number of studies have shown that the work productivity of semi-starved laborers could be increased markedly by supplementing their energy intake (Diaz et al., 1991; Viteri, 1971; Viteri and Torun, 1975; see also reviews by Conzolazio, 1983; Spurr, 1986, 1990). Weight losses in some of the historical studies were also complicated, undoubtedly, by deficiencies of certain nutrients, such as individual vitamins and minerals. Iron deficiency anemia, for example, induces decrements in physical performance (Edgerton et al., 1979; Finch and Huebers, 1982; Gardner et al., 1977) that can be reversed by iron supplementation (Edgerton et al., 1979).

Multiple variables are known to complicate the evaluation of physical performance during periods of weight loss. Measured decrements in physical performance vary with the test procedure being used. Decrements in U.S. Ranger performance were best demonstrated by the incremental dynamic lift, a maximal lift capacity test (Moore et al., 1992). Load-lifting capability fell progressively by an average of 30 to 40 lb as Ranger training progressed to the third and fourth periods. The magnitude of performance decline correlated well with the percentage of weight lost by individual soldiers. In this study, a higher correlation was evident when decrements in lift capability were compared to losses in fat-free mass. In contrast, handgrip strength failed to show measurable decrements in the Rangers, even in the face of high percentages of body weight loss. Recently developed tests of jumping ability tend to yield performance data comparable to those generated by load-lifting tests (see Friedl, Chapter 14 in this volume).

Physical performance tested during prolonged, continuous efforts, such as marching, jogging, or cross-country skiing, can give different results from studies using acute tests of strength. Some of these differences may be due to the type of muscle fibers being affected by the weight loss, that is, fast-twitch versus slow-twitch fibers. And some differences may be dependent on the

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

minute-to-minute availability of body glycogen and intramuscular triglyceride stores and glucose precursors.

Overall physical performance can also be estimated by a subject's oxygen uptake (Vo2 max), with declines being recorded as a percentage of maximal uptake. Declines in Vo2 max) may indicate lowered performance. Heart rates can give roughly comparable data, but these types of measurement are most valuable when performance during short bursts of activity is being assessed (cf., McArdle et al., 1991).

In most studies of weight loss caused by imposed food restriction, the subjects were constantly hungry, and they ate avidly whenever food was offered (cf., Moore et al., 1992; Shippee et al., 1994). Conversely, weight loss during periods of illness, trauma, or emotional disturbances is typically accompanied by voluntary underconsumption and a failure to consume food that is offered or readily available. The problem of lowered consumption by soldiers in field situations would seem to fall into this latter category. 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 a result of a generalized stress response. Ibuprofen has been used experimentally to reduce cytokine-mediated effects of stress, such as loss of appetite (Beisel, 1991). A study of the impact of ibuprofen on appetite may determine if a cytokine-mediated underconsumption situation would disappear with ingestion of an agent that blocks cytokine formation.

In summary, historical evidence combined with recent detailed studies of weight loss during military special forces training suggest that essential physical performance is maintained in most individuals until hydrated weight loss approaches 10 percent of initial weight, provided the rations available are of adequate nutritional composition. Research has demonstrated a correction of physical performance deficits when nutritional deficits are adjusted for a sufficient time to recover lean tissue losses.

Many variables must be considered when assessing this relationship between physical performance and weight loss. These include the nature and duration of the physical performance being studied, the tests used to assess performance, and the body composition at the time of testing (in terms of losses in body fat, body fat-free mass, and key body nutrients, such as vitamins and minerals, body fluids and electrolytes, and the availability of body glycogen and intramuscular triglyceride stores and carbohydrate precursors).

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×
Impact of Suboptimal Consumption of Military Operational Rations on Cognitive Performance

As reviewed by LTC Mary Z. Mays (see Chapter 15 in this volume), the effects of suboptimal ration consumption on cognitive performance paralleled the effects on physical performance, but there were many fewer studies. If weight loss can be equated with underconsumption, decrements in cognitive performance resembled those in physical performance in that no effects of minor degrees of weight loss were detected in tests of cognitive performance. Deficiencies in performance in these studies only began to appear when weight losses in well-hydrated soldiers approached or exceeded 10 percent of body weight (see summary in Table 1-2). An important consideration is hydration status. Studies with Air Force personnel have clearly demonstrated significant declines in cognitive performance with 5 to 10 percent losses in body weight over 24 hours or less because of dehydration (Altman and Fisher, 1986).

LTC Mays provides a number of pertinent answers to the related questions ''Why do soldiers consume less than the full ration?" and "What factors influence this lowered consumption?" LTC Mays points out that the conditions which give rise to lowered operational ration consumption are really quite harsh and include such problems as severe climatic and environmental conditions, extreme fatigue, dangerous training scenarios, and tremendous energy expenditures. All of these factors combine with the unique nature of the rations themselves and the unattractive conditions under which the rations must sometimes be eaten.

In interpreting field data, it is impossible to differentiate among the effects of lowered consumption on cognitive performance, the effects of the field setting itself on cognitive function, and the adverse physical and emotional factors just mentioned. These factors certainly affect the eating behavior of soldiers in such settings.

The concern of military personnel to meet body weight standards also must be considered. Many soldiers think of peacetime field training periods as an excellent opportunity to reduce dietary intake and to lose weight to meet these standards. When asked prior to field training exercises about their desire to lose or gain weight, 12 to 86 percent of soldiers intended to try to lose weight during the upcoming exercises (Edwards et al., 1989; USACDEC/ USARIEM, 1986; see Baker-Fulco, Chapter 8 in this volume). This attitude could contribute to voluntary food restriction during training.

Similar to the tests used to assess physical performance, tests of cognitive performance are subject to many variables present in the field setting. Studies of mood are often difficult to interpret, as are soldier self-reports about their performance decrements. At present, the Military Nutrition Division at USARIEM and the food products group at NRDEC do not use a standardized test battery for cognitive testing (see Mays, Chapter 15 in this volume).

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

TABLE 1-2 Research Depicting Body Weight Loss and Changes in Performance in Military Personnel

Study

Duration (days)

Relative Δ (%) Body Weight

Performance Tests

Test Results

Physical Performance

Consolazio et al., 1979

10

NC*

Vo2max

-2.0%

Teves et al., 1986

44

NC

Maximal lift

NC

Askew et al., 1987 (MRE)

30

-1.6

Grip strength, ILE§, Vo2max

NC, NC,-10.2%

Askew et al., 1986

12

-2.8

Vo2max, 2-h run performance

5.7%, NC

Roberts et al., 1987 (RCW)**

10

3.0

ILE

NC

Consolazio et al., 1979

10

-3.6

Vo2max

11.0%

Consolazio et al., 1979

10

-3.7

Vo2max

-7.4%

Roberts et al., 1987 (MRE)**

10

-4.0

ILE

NC

Askew et al., 1987 (RLW-30)

30

-5.0

Grip strength, ILE, Vo2max

NC, -8%, -14.8%

Consolazio et al., 1979

10

-5.0

Vo2max

+5%

Taylor et al., 1957

12

-7.4

Vo2max

-4.0%

Johnson et al., 1976

60

-9.4

Vo2max

-14.1%

Taylor et al., 1957

24

-10.2

Vo2max

-10.1%

Frykman et al., 1993

60

-13.0

Maximal lift, jump power

-21%

Johnson et al., 1994

60

-16.0

Maximal lift, grip strength

-24%, NC

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

Cognitive Performance

Askew et al., 1987

10, 30

-1.6, -5.0

Vigilance, encoding

NC

Askew et al., 1986

12

-2.8

Various

NC

Roberts et al., 1987

10

-3, -4

Various

NC

Crowdy et al., 1982

12

-3, -6

Marksmanship, vigilance, arithmetic, coding

NC

Shippee et al., 1994 (Benning Phase)

13

-6.0

Decoding, memory, reasoning, pattern recognition

NC

Hirsch et al., 1984

34

<-5% or >-7%††

Battery of cognitive and psychomotor tests

NC

Shippee et al., 1994

60

-12.6

Decoding, memory, reasoning, pattern recognition

-10 to -34%

Keys et al., 1950

60

-16.0

Memory, reasoning, spatial perception

NC

* NC, no change.

† Vo2 max, changes in Treadmill Maximal Oxygen Intakes; measures aerobic capacity.

‡ Maximal lift, measures strength; can be confounded by skill level.

§ ILE, isokinetic leg extension; measures strength.

** High urine specific gravity results suggest that a significant amount of the weight losses in this study may have been due to dehydration.

†† Number of subjects in each group = 8.

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

Standardized cognitive test batteries are used in other military research and would be useful in studies of ration intake.

It is also difficult to gather reliable baseline data on soldier food intake patterns. For example, the sudden appearance of dietitians taking notes, asking questions, and documenting soldier eating patterns can hardly be expected to produce normative data. It is also difficult to establish realistic control groups. The motivation of the soldiers being tested can vary greatly, with problems of both over- and undermotivation and a tendency to approach testing as game playing. Analysis and reporting of data can also introduce problems. Group means provide little information about extremes that might be present among group members.

Due to deficiencies in available data, it might be useful to evaluate other models of underconsumption, such as anorexia nervosa, illness, malignancy, trauma, aging, weight control used by athletes, and studies of fasting and food deprivation. Animal models may not be appropriate, because food deprivation in animals may cause increased alertness and activity. In addition, the effects of mood, motivation, and relevant contextual and cognitive factors cannot be tested with animal models.

In summary, the small amount of data available suggests that lowered energy intake may degrade cognitive performance when it leads to weight loss greater than 10 percent of body weight over 4 or more weeks. Research that addresses the cognitive aspects of underconsumption should include monitoring of body weight and cognitive performance at all stages of each study. Care should be taken to include longitudinal studies with good baseline measures of body weight, some indicators of body composition for each participant, and initial cognitive performance scores. Future experimental designs should eliminate (or minimize) serious problems found in previous research, such as the establishment of suitable control groups, normative baseline control data, cognitive test standardization and reliability, test condition standardization, subject motivation, and measure performance over a range of body weight losses.

Implications of Underconsumption of Macronutrients

Related to the underconsumption of military operational rations is the optimum composition of rations in terms of the macronutrients carbohydrate, fat, and protein. These issues were considered by Stephen D. Phinney in Chapter 16 and Carol J. Baker-Fulco in Chapter 8. As early as the first half of this century, there was a strong difference of opinion between nutritionists who advocated a high-carbohydrate, low-fat diet for optimum physical performance and polar explorers who, for reasons of practicality, advocated compact high-fat rations, such as pemmican, which was developed during World War II. An experiment was conducted with Canadian military personnel who were

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

abruptly switched from their usual ration to a dried meat and fat ration (pemmican) as their sole source of energy. Arctic maneuvers requiring high energy were carried out, and the soldiers became debilitated in 3 days (Kark et al., 1946). In contrast, Stefanson, a former arctic explorer, lived successfully and actively for a year at the Russell-Sage Research Institute, Bellevue Hospital in New York, on a diet exclusively composed of meat, fat, internal organs, and bone marrow (McClellan and Dubois, 1930). The key to the utilization of high-fat diets, as pointed out by Phinney (see discussion in Chapter 16 in this volume), is the critical nature of a period of adaptation, appropriate vitamin and mineral supplementation, plus energy expenditures at a high enough level to utilize the fat consumed.

One of the issues of concern with diets of this nature that are low in or devoid of carbohydrates is the development of ketosis. Phinney and colleagues fed five highly trained cyclists a ketogenic diet composed of 15 percent protein, 0 percent carbohydrate, and 85 percent fat, which supplied 1.75 g of protein per kg of body weight per day. The diet was supplemented with vitamins and minerals including 3 g of sodium. The cyclists were studied at rest and with exercise. It took 3 weeks to adapt to the diet, and by the fourth week both endurance time and peak aerobic power had returned to baseline values (Phinney et al., 1983). While the data were collectively presented as a mean for the five cyclists (individual performance measures varied), this study emphasized the need for a period of adaptation and adequate amounts of sodium, calcium, and magnesium. The study described by Phinney suggests that, under the conditions of his experiment, there is no metabolic requirement for dietary carbohydrate because sufficient carbohydrate can be synthesized from glycerol and amino acids to prevent ketosis.

However, the importance of dietary carbohydrate to maintain a high level of physical performance, including endurance, is generally accepted (Evans and Hughes, 1985; Hargreaves, 1991). The carbohydrate needs of elite athletes were recently reviewed by Williams (1993). In this review actual measured carbohydrate intake of a variety of male athletes ranged from 373 to 596 g/d with energy intakes of 3,034 to 5,222 kcal/d. Corresponding data for female athletes were 290 to 428 g of carbohydrates per day with energy intakes of 1,931 to 3,573 kcal/d. In a comparison of food intake across military field feeding trials, Carol J. Baker-Fulco (see Chapter 8 in this volume) found that carbohydrate intake was typically less than 400 g/d. After reviewing many studies, Williams concluded "the question of how much carbohydrate should be consumed cannot be answered with any great precision" (Williams, 1993, p.56). This statement is appropriate not only for athletes but also for troops in the field.

In an earlier report, the CMNR reviewed a proposed high-density, high-fat special operational ration designed to minimize weight and space for military units on extended patrol when they were carrying all of their food and equipment. Because of the concern that troops would not likely be adapted to

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

a high-fat ration, it was recommended that this specific ration also should provide a minimum of 400 g of carbohydrate per day to prevent a serious problem of ketosis if troops were fed this ration with no period of adaptation. An adequate level of carbohydrate would aid in maintaining and restoring muscle glycogen, and help sustain performance and prevent chronic fatigue in physically active troops. In addition, this level of carbohydrate would prevent the development of ketosis and the resultant adverse performance that may occur in troops not adapted to the high-fat diet (IOM, 1992b).

In his review, Stephen D. Phinney (see Chapter 16 in this volume) discusses energy deficits resulting from reduced food intake, illness, injury, or increased physical activity. Depending on circumstances and hydration state, early weight loss will include loss of water, loss of body fat, and loss of lean body mass unless protein intake is maintained at a high level. Energy deficits induced by increased physical activity are not likely to result in loss of lean body mass if protein intake is maintained at least at 1 g per kg of body weight per day, according to Phinney. Energy needs can be calculated as described by the Recommended Dietary Allowances (RDA) Committee (NRC, 1989) or estimated most accurately using the doubly labeled water technique (Jones et al., 1993). Pavlou (1993) recently described equations that can be used to predict the energy needs of athletes. The protein needed for high-level physical performance was defined by Evans (1993) as 1.2 g per kg of body weight per day and by Lemon (1991) as 1.2 to 1.7 g per kg of body weight per day depending on the event (12–15 percent of energy intake). At the levels of energy intake that occur with increased physical activity, and with the increased efficiency of protein utilization that occurs with higher energy intake, protein at 12 to 15 percent of energy intake (assuming protein quality typical of a typical American diet) should easily provide enough dietary protein. In field trials with operational rations, mean protein intakes typically are 100 g for men and 80 g for women (see Baker-Fulco, Chapter 8 in this volume).

Whether the results of these studies on athletes can be applied to troops in the field can be questioned. The athletic events range from running and swimming to a variety of team sports. The term elite athlete typically denotes a high level of physical performance, not necessarily a specific energy expenditure. Troops in the field often expend 3,000 to 4,500 kcal/d, and in many respects they resemble elite athletes in this context. The CMNR believes that the data obtained with athletes are relevant to troops in the field under these conditions.

In summary, these examples suggest that physical performance is well maintained during undernutrition if adequate protein, vitamins, and minerals are supplied and loss of lean body mass is minimized. Phinney recommends that protein should be supplied at 1 to 1.5 g per kg of body weight per day, preferably at the higher level. Supplying at least 100 g of carbohydrate per day in the standard operational ration that contains a maximum of 160 g of fat is desirable to prevent ketosis. Research with military personnel under various

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

field training conditions indicates that protein intake is typically adequate, while energy and carbohydrate intakes are lower than desired.

ATTRIBUTES OF EATING THAT AFFECT CONSUMPTION

The Physical Eating Situation

For the soldier, the military eating situation can vary from highly monotonous and predictable to continually changeable and highly unstable. In garrison, dining hall managers strive to provide a variety of foods in a comfortable setting, and current approaches include both varied menus with many alternative item choices and nutrition education materials to enhance healthy eating habits. Nonetheless, the image of the military dining situation remains negative. In a study that compared the ratings by military personnel of Navy dining halls with commercial foodservice establishments for 16 different aspects of foodservice, the Navy foodservice scored significantly lower on all aspects of foodservice with the exception of air quality (Navy dining halls are smoke-free). Factors as disparate as temperature of the dining areas, lighting, taste of food, number of items per meal, and portion size all received significantly lowered ratings (Salter et al., 1990; see Cardello, Chapter 10 in this volume).

There are a number of factors that often lead to soldiers skipping meals or reducing their intakes. In the field, soldiers typically do not have the opportunity to eat under cover, and it is often difficult to prepare or eat a meal. In addition, the physical demands of training or field exercises coupled with the additional stress of high performance expectations may result in soldiers choosing to rest or complete a mission instead of eating. The process of deployment or transportation to the field can involve long periods of time and leaves little opportunity for soldiers to eat or drink. In one study, the average hydration and body weight changes during a 24-h deployment were approximately half of the changes observed in the total 11-d training period (Popper et. al., 1987; see Kramer, Chapter 17 in this volume). Hypohydration has been shown to decrease food intake, and therefore a suboptimal hydration status may lead to reduced food intake (see Engell, Chapter 12 in this volume). Ration consumption in the field may also be affected by changes in circadian rhythms, soldiers' attitudes toward weight loss and food intake while in the field, meal timing, meal frequency, meal duration, meal regularity and predictability, ease of access to the food, food appropriateness, and lack or reduction in food sensory cues due to packaging. All of these factors have been shown to affect food intake adversely in experimental settings (see Kramer, Chapter 17 in this volume).

As described above, eating is associated with many nonfood factors that constitute the entire eating event. The setting in a dining room or cafeteria,

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

silverware, familiar dishes, and a table and chair at a comfortable height for dining are examples of specific nonfood cues that are linked to beginning and ending a meal (Weingarten, 1984). In the field setting, soldiers have few of these cues, and often wind, sand, dirt, or temperature factors contribute to making the eating of a meal not only unpleasant but difficult. Results from conditioning studies with animals and humans indicate that familiar nonfood cues tend to stimulate eating and metabolic responses (Cornell et al., 1989; Woods et al., 1977). These studies show that familiar nonfood cues stimulate additional eating or a desire to eat even after an individual is satiated or there is no food available. As discussed by F. Matthew Kramer (see Chapter 17 in this volume), familiar nonfood cues in the eating situation play a role in anticipatory learning (Moore-Ede, 1986; Woods, 1991), and a lack of cues may reduce the desire to eat. Combat, or the prospect of imminent combat, also will tend to increase anxiety and decrease appetite. Adequate time and appropriate times to eat also become important under these conditions.

In summary, the field setting, and often deployment to the field setting, include many factors that reduce soldiers' desire to eat or to reduce their food intake. Whenever possible, deployment to field training exercises should provide ample opportunities for soldiers to eat and drink. The resulting exercises should take into account changes in circadian rhythms, meal timing, and the appropriateness of meal items to encourage food intake. Providing meals in a more typical meal setting at tables should be encouraged. The literature in environmental psychology and acquisition of learned behaviors provides a strong theoretical base for understanding the impact of the eating situation on food intake, but more research is needed specifically to address issues of increasing rather than decreasing food intake in general, and in military field settings in particular.

Social Facilitation of Food Intake

The social environment plays a prominent role in determining human behavior. Social facilitation of behavior, or an increase in the frequency or intensity of an individual's behavior in the presence of others engaged in a similar behavior, is a frequently observed phenomenon (Zajonc, 1965). In Chapter 20 of this volume, John M. de Castro reviews his own and others' research on social facilitation and human food intake. This research demonstrates that, under laboratory conditions, individuals consume more food in the presence of others than when eating alone (e.g., Berry et al., 1985; Conger et al., 1980; Goldman et al., 1991). However, these studies may not be very relevant to the field situation because the effects of social facilitation were only examined using single meals consumed in an artificial laboratory environment.

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

To determine if social variables also could influence the food intake of free-living individuals, de Castro and colleagues used a diet diary technique in which subjects recorded meal time and location, food and drink consumed during the meal, affective state, and the number and identity of other people eating with them (de Castro, 1990, 1994; de Castro and Brewer, 1992; de Castro and de Castro, 1989). Results of these studies revealed that meals eaten with other people were substantially larger than meals eaten alone. The greatest increase in intake was observed when individuals went from eating alone to eating with one other person. However, it should be noted, the more people who were present, the larger the meal consumed (de Castro and Brewer, 1992). The direct relationship between the number of people present and meal size was observed for meals consumed as breakfast, lunch, or dinner; in restaurants or at home; and on weekdays or weekends. Although social facilitation of feeding was observed regardless of the identity of the eating companion, it was more pronounced when meals were consumed with family or friends than when meals were eaten in the presence of other individuals (de Castro, 1994). On the basis of this research, de Castro hypothesizes that the presence of other individuals, particularly family and friends, may augment food intake by (1) increasing verbal interactions that would result in longer meal durations and thus increases in the amount of food eaten, and (2) relaxing the individual and thereby decreasing inhibition of food intake.

In summary, research on social facilitation of feeding suggests strategies that could be employed to increase consumption of military operational rations. For example, if strategically feasible, allowing soldiers to eat in pairs or larger groups could promote intake of rations. Intake might be particularly enhanced if groups were composed of individuals who knew each other well, and if the situations were conducive to verbal interactions that could increase meal duration. If the preceding conditions cannot be met in the field, de Castro suggests that modeling behavior where one soldier is instructed to eat large amounts in the presence of soldiers who consume smaller amounts or where direct orders are given from commanding officers might increase intake of rations. Clearly, however, in a combat situation, the ability to increase food consumption through improvement of physical and/or social factors is limited.

Commanders' Perceptions and Attitudes about their Responsibilities for Feeding Soldiers

As an extension of the modeling concept, it is apparent that the attitude of the leader in the field regarding ration acceptance will affect ration consumption. A survey by Celia F. Adolphi of former commanders attending the Army War College in 1991 provided initial information on commanders' understanding of the relationship of diet to soldier performance (see Chapter 5 in this volume). Of the 113 responding to the survey, 50 percent of whom

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

had commanded combat units, only 7 percent could answer correctly 10 nutrition knowledge questions. These results were remarkable in comparison with a group of basic trainees, of whom 64 percent could correctly answer the same nutrition questions. In addition, only about half of the commanders thought there was a positive relationship between diet and the combat performance of their troops. When asked to rank order their rationale for determining what type of rations to use during field operations, the top three reasons given were training scenario, time to prepare rations, and soldier preference. Slightly over half were involved in decision making about rations. Respondents indicated that information on nutrition came from drill sergeants, master fitness trainers, physician assistants, or popular magazines. Commanders commented that soldiers purposely planned to lose weight during field training. Provision of nutrition education 2 to the various levels of supervision in the military could help improve commanders' appreciation of the diet/performance relationship.

A number of possible mechanisms were proposed by Adolphi as an outgrowth of the commanders' survey (see Chapter 5 in this volume). In addition to conducting an ongoing survey of commanders and soldiers returning from Somalia or other nonwar operations, she recommended the following:

  • include hierarchical and progressively more complex health promotion (including nutrition) in U.S. Army Training and Doctrine precommand and command courses;

  • train physician assistants to teach the fundamentals of diet and performance (since they are the only medical personnel who interface with soldiers);

  • provide USARIEM Technical Note 93-3 (Thomas et al., 1993), Nutrition for Health and Performance: Nutritional Guidance for Military Field Operations in Temperate and Extreme Environments, to commanders; and

  • periodically survey Army War College and Command and General Staff College classes to measure understanding of the importance of ration consumption to performance.

Eating Situations, Food Appropriateness, and Consumption

A number of factors including appetite, hunger, liking, availability, and appropriateness of the food contribute to human food consumption. In Chapter 18

2  

The recently revised USARIEM Technical Note 93-3 (Thomas et al., 1993), Nutrition for Health and Performance: Nutritional Guidance for Military Operations in Temperate and Extreme Environments, provides information in an understandable format.

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

in this volume, Howard G. Schutz evaluates the role of the appropriateness of a food item to the eating situation in governing food intake. Appropriateness of a particular food can vary according to meal occasions, attitudes about the food, and the physical and social environment. Consumer behavior studies and cognitive-context research indicate that individuals have definite ideas about the appropriateness of a food for given occasions (e.g., meals versus snacks; breakfast versus dinner; family meals versus special occasions), particular contexts (e.g., cold days versus warm days), and specific individuals (e.g., adults versus children, men versus women) (Belk, 1975; Hugstad et al., 1975; Miller and Ginter, 1979; Schutz, 1988). Results of this research indicate that measures of hedonic qualities of a food or food acceptance do not necessarily predict how appropriate the food will be rated for a given situation. For example, although three meat products may have similar acceptance ratings, the appropriateness ratings for the three may differ significantly as a function of the context in which the foods are assessed. On the basis of this research, Schutz proposes that foods are less likely to be consumed when they are served in an inappropriate use situation than in an appropriate use situation.

In summary, research suggests that, if possible, consideration should be given to the appropriateness of the items contained in the ration to situational variables including the time of day, temperature, and social environment. Providing appropriate foods might result in an increased intake of rations.

ATTRIBUTES OF FOOD THAT AFFECT CONSUMPTION

Food Stereotypes and Food Image

Military operational rations and garrison food have a negative image both with the American public and with the soldier. This image is perpetuated in the media through articles whenever soldiers are deployed and, more consistently, through well-known, long-standing comic strips such as ''Beetle Bailey." In a recent questionnaire, active-duty soldiers rated the expected acceptability and expected quality of 12 different foods as served in 7 different types of commercial and military eating establishments (A. V. Cardello and R. Bell, U.S. Army Natick Research, Development and Engineering Center, Natick, Mass., unpublished manuscript, 1995; see Cardello, Chapter 10 in this volume). The 12 food items listed in the questionnaire were selected to represent both items where the quality would be expected to vary with the location of preparation (e.g., steak) and items for which the expected variability would be less (e.g., soda). For all food items, in terms of both expected acceptability and quality, food prepared and served at home received the highest rating while responses to military food clustered at the lowest ratings, along with hospital and airline foods, for all food items. Because the subjects in the first study were all familiar with military food, the same

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

questionnaire was also administered to an age-matched group of students who had never eaten military food. The students' results were similar and therefore indicated that a negative image of military food is widespread in the general population and is not necessarily related to exposure to the food itself. These findings have been supported by a study of food acceptability in Navy dining facilities (Salter et al., 1990; see Cardello, Chapter 10 in this volume). Hedonic properties of military foods—flavor, variety, and appearance—are the primary factors that contribute to this poor image of military foods (A. V. Cardello and R. Bell, U.S. Army Natick Research, Development and Engineering Center, Natick, Mass., unpublished manuscript, 1995). In addition, civilians indicated that movies and television shows were the source of their poor opinion of military foods, whereas soldiers indicated that their opinions were based on early experience with military foods during training.

Product acceptance is not only a result of the intrinsic quality of the food. It can also be related to appetite and to the expectations a consumer has for a food item and the degree to which the food matches these expectations (Cardello, 1994; Cardello and Sawyer, 1992; see Cardello, Chapter 10 in this volume). The bulk of consumer psychology research supports an assimilation model (Sherif and Hovland, 1961) for predicting the relationship between food quality and acceptability. As discussed by Armand V. Cardello in Chapter 10 in this volume, for military operational rations this model predicts that if expectations for rations are low, then acceptance of the rations will be low. Given the poor image of military operational rations among both soldiers and civilians, continued poor acceptance of even the newly developed rations would be expected. The assimilation model also predicts that if expectations are changed, then ration acceptance should improve. Informational variables such as packaging can play an important role in changing consumer expectations and, hence, acceptance. Acceptance and food preferences have been shown to contribute significantly to variability in food consumption (cf., Smutz et al., 1974; Wyant et al., 1979). In recent studies, soldiers rated food products in military packaging lower and consumed them less than the same products in commercial or "commercial-like" packaging (Kalik, 1992; Kramer et al., 1989). NRDEC also has developed several film clips to attempt to positively change military and civilian expectations, hence acceptance, of operational rations. The two films presented at the workshop effectively used humor to present the message that the MREs were new and improved. The scientifically measured impact of these and other similar media approaches to changing the poor image of rations is a promising area of research.

In summary, military food products have a poor image both among soldiers and civilians. These stereotypical negative expectations appear to be based not only on experience with the food items but also on exposure to mass media. Current models of consumer psychology and recent research with military food packaging indicate that acceptance and intake of military rations may be enhanced by adopting a more commercial-like package. Additional

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

research is needed on the most effective attributes of this packaging and the effects of packaging changes on intake of individual food items, as well as on an entire meal. Based on the assimilation model, improving the image of military food through media and packaging could make a significant change in ration intake. Recent media approaches that incorporate humor into the marketing of new rations have the potential to change both civilian and military images of rations.

Food Quality, Quantity, and Variety

In Chapter 11 in this volume, Barbara J. Rolls discusses how food intake and satiety are influenced by the composition and presentation of foods. The basic question is whether available knowledge regarding food satiety and diet variety could be applied to diet formulation to increase energy intake among soldiers. She noted that palatability is a key determinant of energy intake among humans, although other characteristics may also be important.

Foods that are highly palatable will initially be consumed in greater quantity than less palatable foods. But palatability falls as a given food (and related foods, such as sweets) is eaten (de Graaf et al., 1993). Palatability for unrelated foods is unaffected, however, a fact that promotes variety in eating (Rolls et al., 1984). There are several bases for such changes in palatability, but one can use this knowledge to maximize palatability throughout a meal so as to increase intake. Over the longer term, however, monotony becomes an important factor in food intake. For example, repeated presentation of canned meats makes them unpalatable. The development of such aversions is not a property of all foods. The palatability of foods such as fruit, sweets, cereal, dairy products, bread, or coffee does not decrease as a consequence of repeated presentations (Schutz and Pilgrim, 1958; Siegal and Pilgrim, 1958). Such knowledge should allow the construction of diets that frequently include items showing no aversion over time, while varying those that do.

Among other dietary characteristics important to intake is the energy density of foods (Duncan et al., 1983). Low-energy dense foods can be satiating, despite their low-energy content (e.g., soups) (Kissileff et al., 1984; Rolls et al., 1990). High-density foods appear to be less satiating. These foods often contain higher amounts of fat, and current data suggest that satiety signals are not strong for dietary fat. Fat-containing foods thus tend to be overeaten (except possibly in young, normal-weight men) (Rolls and Shide, 1992; Rolls et al., 1992).

Another factor important to food intake is the fiber content of foods. Diets high in fiber reduce food intake, although the basis for this effect is not well understood (Levine and Billington, 1994). Food intake is also affected by portion size, with greater intake occurring when portion size is larger (Booth et al., 1981; Edelman et al., 1986; Shaw, 1973). Greater energy intake can also

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

be promoted by the supply of energy-containing beverages; liquids as vehicles for energy tend to be less satiating than solids (Tournier and Louis-Sylvestre, 1991). Finally, the perceptions about foods may influence their intake, but there is too small a knowledge base to allow definitive statements on this relationship.

In summary, the key concepts for maximizing energy intake based on food quality and variety are the following: (1) the initial palatability of foods should be high, with self-selection allowed whenever possible; (2) the diet should be as varied as possible; (3) portion size should be as large as practicable; (4) diets should not contain undue amounts of fiber; and (5) energy intake may be enhanced by providing energy-containing beverages.

Food as a Product

Eileen G. Thompson's presentation (see Chapter 13 in this volume) offers interesting perspectives based on industrial food products research. First, she mentions the value of studying the subject in as unobtrusive a manner as possible to learn about eating habits in each environment. Second, she offers insight into factors that affect food palatability, choice, and acceptability and possibilities for increasing energy intake among soldiers.

Regarding the first issue, one must know the target population. Soldiers in garrison are different from soldiers in the field, as office workers are different from construction workers. Their natural eating habits need to be examined in situ in order to determine their food habits, likes, and dislikes. Such observation needs to be unobtrusive and can be accomplished via cameras and by methods long used by anthropologists. To determine the dietary preferences for the soldier in the field, whose diet is prescribed and proscribed, it may be revealing to identify and study a closely matched group in general society, for example, young male construction workers. The importance of this approach is underscored by the likelihood that in looking at a matched group, one accounts for lifestyle similarities in physiological state.

Thompson also offers insight into how to optimize available foods to reach the desired objective from the industry perspective. First, to increase product acceptability (and demand for it), a valid approach is to find a combination of products that optimizes overall product line use. Industry may test the preferences for different flavors of a given product, and rank them accordingly, but it does not then simply choose the highest ranked selections to produce and market. An analysis is conducted to determine the selection of flavors (or other characteristics) that would provide the greatest overall acceptance of the product. The final mix may be different from simply the most highly rated choices. Such an approach may be of use to the military in creating variety in rations to optimize acceptance. Second, she discusses a result that might be of

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

relevance to soldiers in the field: snacking behavior, particularly the so-called "random nibbling" phenomenon. If snacks are available at hand during work periods, they tend to be consumed continually without thought. Such nibbling behavior can lead to significant energy intake each day (Jenkins et al., 1989). If the problem for soldiers in the field is that they do not consume enough energy, maybe an analog for random nibbling would be desirable. Third, Thompson notes that packaging may affect acceptability among soldiers, as it does among civilians, and should be examined. And finally, regarding sensory issues, seasonings are being used more and more in industry to enhance variety and acceptability of food products, with great success. This approach may be relevant for the military as well.

Beverage-Food Interactions

Dianne Engell (see Chapter 12 in this volume) discusses the relationship of water intake to survival and performance. She focuses her discussion particularly on the factors that influence fluid intake and on how fluid intake affects energy intake.

She and her colleagues have examined the impact on MRE consumption and energy intake of the types of beverages supplied with these meals. As noted earlier, fluids can be a significant energy source. Engell states that energy intake from beverages in the early MREs was 8 to 10 percent of total calories (Engell et al., 1987; Hirsch et al., 1985; Popper et al., 1987); this percentage rose to 15 to 17 percent when flavored fruit drinks were provided (Lester et al., 1989; Popper et al., 1987), and reached 20 percent when flavored shakes were supplied in the MREs (Lester et al., 1993). The results indicate that as the number of energy-containing beverages in the MREs has increased, their consumption has led to increases in total energy intake.

Engell also discusses how fluid consumption affects energy intake from solid foods. Several studies show that when fluid intake is restricted, food intake and body weight fall (Adolph and Wills, 1947; Adolph et al., 1947; Bass et al., 1955; Engell, 1988). This effect is related to the state of hydration over time, rather than to peripheral thirst sensations or to the need to lubricate foods (Engell, 1993; Rolls et al., 1990). Such results indicate the importance to energy balance of ensuring adequate fluid intake to maintain normal hydration.

Finally, she discusses some of the factors that influence fluid intake. Her studies show, for example, that accessibility has a strong influence on intake, when studied in garrisoned troops (Engell and Hirsch, 1991). In the field, data are available showing that water is perceived as being less accessible, which suggests that intake may be less than desirable. Daily fluid intake is also influenced by the setting: the largest portion of daily fluid intake accompanies meals and is influenced by social circumstances. Finally, the intake of fluids

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

is strongly influenced by their hedonic attributes, although this relationship has not been carefully examined in field studies.

In summary, the key points regarding fluid consumption and fluid related energy intake among troops in the field are: (1) improve hedonic qualities and variety of beverages supplied in the field to increase fluid intake, (2) optimize social settings in the field (e.g., mealtimes) to enhance fluid intake, (3) increase the convenience of obtaining water in the field, (4) encourage officers to promote increased fluid consumption among troops, and (5) conduct further research on the factors that influence fluid consumption and on the use of fluids to enhance energy intake.

Biological Rhythms and Timing

In Chapter 19 of this volume, Franz Halberg and colleagues discuss the influence of alterations in the diurnal pattern of food intake on physiologic functions of the body. In particular, Halberg's work has shown that the ingestion of a single daily meal in the evening promoted better weight maintenance than one consumed in the morning. A careful examination of meal timing in relation to the daily performance cycle in military personnel in the field might thus reveal if meal timing might be useful in optimizing body weight and performance.

NEW CHANGES IN MILITARY OPERATIONAL RATIONS AND FIELD FEEDING

Ration Evolution

Development and testing of military operational rations has been an ongoing component of the military, and the use of nutritional standards for rations has been in place since World War II (for a review see Schnakenberg, Chapter 6 in this volume). All military rations are expected to meet the Military Recommended Dietary Allowances (MRDAs) (see AR 40-25, 1985) with the exception of restricted rations, which are currently the Ration, Lightweight; the Long Range Patrol Food Packet; and the Survival General Purpose, Food Packet. There are also separate specifications for these restricted rations, which are provided to sustain soldiers for no more than 10 days. Testing of military operational rations is prescribed in procedures and policies approved by the Office of the Surgeon General (OTSG) of the Army and is conducted jointly by USARIEM and the Sustainability Directorate at NRDEC.

The MRDAs (included in AR 40-25, 1985) define both the recommended allowances for evaluating what people should consume and nutritional standards for development and procurement of the ration. However, the criteria

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
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for testing rations are not specified, and USARIEM has had a major role in their development, as did the OTSG of the Army.

Prior rations have included the K Ration in World War II and the C Ration (Meal, Combat Individual) in tin cans during World War II and Korea (see Schnakenberg, Chapter 6 in this volume for a more detailed history). The MRE ration was developed to replace the C Ration in the 1970s and 1980s and can be used for up to 21 days (U.S. Department of the Army, 1995).

Many constraints exist in developing rations (see Darsch and Brandler, Chapter 7 in this volume). These constraints include acceptance, nutrition, wholesomeness, productivity, cost, sanitation, cultural appropriateness, variety, usage in a variety of environments, the need for withstanding air drops, shelf life equal to or greater than 3 years, minimal weight and size, and the capacity to self-heat and be assembled in modules tailored to the ration needed. In addition, the packaging must be protective in response to nuclear, biological, and chemical threats during war. Finally, there are performance enhancement characteristics that may affect the formulation of specific components (IOM, 1994).

The program of continuous field improvement is reviewed in depth for all classes of rations by Gerald A. Darsch and Philip Brandler in Chapter 7 and Edward Hirsch in Chapter 9 of this volume. A review of the ration types is included earlier in this chapter.

A new combination, the Unitized Group Ration (UGR), has been developed to simplify logistics of ordering and meal preparation in the field. The UGR uses components of the A Ration (without the perishables), the B Ration, the T Ration, and additional brand-name items combined in a unified system. Fifteen breakfast and 30 lunch/dinners are available. The UGR increases field feeding efficiency and reduces the number of items that a cook has to order to get the necessary items for a meal.

Based on direct feedback from Desert Shield/Storm, the OTSG of the Army, and the CMNR, an increasing emphasis is being placed on nutritional labeling and nutrition information on operational rations. Guidelines are now being developed to provide appropriate consumer-oriented information.

In the future, the goals are to develop self-heating rations with "fresh" quality yet shelf-stable and suitable for both individual and group feeding. Pending further approval, a self-heating group meal is in the planning stages; the meal module would include all accessories, be modularized similar to the UGR, but provide food for 18 soldiers. This concept has been called "Kitchens in a Carton."

In summary, military operational rations are under almost continual revision. Ration developers are concerned to provide the best possible product for their consumers and at the same time be cognizant of the factors related to packaging, shelf-life, transport, and distribution. New developments such as shelf-stable bread products and the flameless ration heater will significantly broaden the scope of food products available for individual rations.

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
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The Current Situation with Army Field Feeding

Some of the major problems faced by the Army with feeding troops in the field include logistics, time, the quality of the food preparation and packaging, the lack of hot/cold alternatives with certain food items, and the lack of cooks in the forward areas. Added to these problems are the realities of combat itself. The MRE has some advantages in these circumstances, but when it does not include a flameless heater, lack of hot foods is still a significant deterrent to energy intake (for a discussion, see Motrynczuk, Chapter 4 in this volume).

The logistics of supply may thus play a role in underconsumption of rations. The military feeding system in the field in the recent past, based on Army field feeding policy, has relied primarily on MREs and T Rations unless field kitchens were accessible. The policy was that commanders should provide soldiers with two T Rations per day and one A or B meal every 3 days. The recent Desert Shield/Storm conflict demonstrated that forward units might well not be supplied with even T Rations for periods of up to 60 days. This situation, in many cases, was the commander's decision, as the commander's responsibility according to policy was to provide soldiers with three quality meals per day, Mission, Enemy, Terrain, Troops, and Time (METT-T) dependent. Thus, long-term consumption of the MREs and any supplemental packs was a frequent occurrence depending on the scenario and the distance from battalion support services. In this environment, depending on time to reach the forward lines, hot meals in the form of T Rations might take 6 to 10 hours, and availability of hot fluids was limited to what the soldier could heat on his own. Thus, the logistics of supply and the system for field food preparation becomes extremely important in long-term support.

In response to the problems encountered in Desert Shield/Storm, a new strategy for field feeding was developed that will provide soldiers with at least one cook-prepared meal (A or B Rations3) everyday and has now been approved by the Army Chief of Staff (Decision to Increase the Number of Military Cook Personnel, unpublished Army doctrine, June 1992). The major changes will be to have an enhanced company-level field feeding truck with two cooks, which will provide hot meals and perishable foods on a daily basis and be able to follow the unit on maneuvers. These field kitchens will be supervised by a foodservice technician at the brigade level who will develop the feeding plan for brigade-size exercises and ensure that the ration fits the unit scenario. This procedure will allow planned variety and provide a specific individual who is responsible for the meal planning. Significant efforts have thus been put forward to improve the component that supply and logistics has in affecting underconsumption of the ration.

3  

A Rations are cook-prepared from fresh or perishable foods; B Rations are cook-prepared from canned or dehydrated foods.

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
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Scenario in the Future

The plan for the future as described by CW4 Peter Motrynczuk (see Chapter 4 in this volume for summary) is to add three more cooks per battalion and to use all cooks in new ways. The plan is to put small mess teams forward; one of these two-person teams will be a soldier with a grade of E-5 with some cooking experience. They will do limited food preparation forward and will have equipment and support to do it with Kitchen Company Level Field Feeding-Enhanced (KCLFF-E) equipment and a high-mobility vehicle (HMV). The equipment forward includes a sanitation center (SC) with materials for preparation and cleanup of B and some A Rations. This center is a component of the mobile kitchen trailer (MKT) with a new container kitchen and a generator to minimize preparation time, to allow food refrigeration, and to permit water storage. Cooks remain in the battalion field training area to do food preparation. Equipment improvements will be made at this level as well.

It is hoped that by having the cooks forward with the assault companies it will be possible to customize food preparation to better fit troops' needs. This proposal is an example of tailoring both the food and the situation to each other, and then adjusting the fit.

In summary, proposed changes in the number and location of Army cooks and their support vehicles may greatly reduce the present logistical difficulties in providing hot meals to soldiers. The improvements outlined by CW4 Peter Motrynczuk are scheduled for implementation in early 1996 and will also allow increased use of a wider variety of food items, including fresh foods.

PROPOSED PLAN OF ACTION BY NRDEC

The research proposal by Edward Hirsch (see Chapter 22 in this volume) is designed to show if certain manipulations in the way troops are fed in the field will lead to increased ration consumption. The proposed manipulations include using a new ration, premarketing the ration system, providing a social setting for the eating situations, and introducing more variety in the system. Other suggested manipulations are to prevent some of the trauma frequently associated with deployment, provide scheduled meals and snacks, create a protected environment for feeding, provide easy ways to heat the ration, and ensure adequate fluid intake. The proposal suggests that company-sized units might be exposed to the variable individually and food intake measured relative to energy expenditure. This demonstration would involve the use of approximately a battalion of troops and involve considerable data collection by a number of investigators. The CMNR is concerned that several of the proposed manipulations may produce an improvement, but provide little data as to whether or not implementation of these changes would result in adequate

Suggested Citation:"1 Introduction and Background." Institute of Medicine. 1995. Not Eating Enough: Overcoming Underconsumption of Military Operational Rations. Washington, DC: The National Academies Press. doi: 10.17226/5002.
×

intake of the modified ration system. The incremental effects of any of these manipulations could not be adequately evaluated, and it might not be possible to recommend a field feeding system that did or did not provide assurance of adequate consumption to meet energy needs.

Instead such a program should first review the data on eating behavior from both military and civilian institutional studies. The best results from this review could be used to construct a multifactorial model concerning the importance of such variables as variety, meal schedules, snacks, feeding environment, social influences, and convenience of food preparation. Such a model would provide a basis for carefully controlled pilot studies to obtain a potential measure of the influence of these variables on intake. From these pilot studies, hypotheses could be constructed utilizing the most likely variables. Those variables that are judged feasible in a military operation could be more effectively tested. A multifactorial modeling approach could thus provide a rationale for obtaining military field test units. The resultant data could be used as a guide to field commanders in utilizing the strategies developed for a field feeding doctrine.

Although the Army has devoted a significant amount of effort to ration development, less consideration has been given to the effects of situational and environmental factors that may have a significant impact on consumption. The stressful environment of the field, particularly combat, certainly impacts on ration consumption, and there may be higher acceptance of certain ration items than others under those conditions. A program for marketing or educating soldiers about the military operational ration and its importance to their performance may be important, particularly when it is known that negative comments from peers, superiors, media, and others can help establish a negative image of military combat rations and thus discourage consumption.

Underconsumption of military operational rations may only be a problem if it has negative impact on physical and cognitive performance. Long-term or repeated usage of rations may result in more significant weight losses and thus may have the potential for larger effects on physical or cognitive performance.

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Eating enough food to meet nutritional needs and maintain good health and good performance in all aspects of life—both at home and on the job—is important for all of us throughout our lives. For military personnel, however, this presents a special challenge. Although soldiers typically have a number of options for eating when stationed on a base, in the field during missions their meals come in the form of operational rations. Unfortunately, military personnel in training and field operations often do not eat their rations in the amounts needed to ensure that they meet their energy and nutrient requirements and consequently lose weight and potentially risk loss of effectiveness both in physical and cognitive performance. This book contains 20 chapters by military and nonmilitary scientists from such fields as food science, food marketing and engineering, nutrition, physiology, psychology, and various medical specialties. Although described within a context of military tasks, the committee's conclusions and recommendations have wide-reaching implications for people who find that job-related stress changes their eating habits.

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