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Introduction and Background

THE COMMITTEE'S TASK

The Committee on Military Nutrition Research (CMNR) of the Food and Nutrition Board (FNB), Institute of Medicine (IOM), National Academy of Sciences (NAS), was asked by the Division of Military Nutrition, U.S. Army Institute of Environmental Medicine (USARIEM), U.S. Army Medical Research and Development Command (USARMRDC), to review current research pertaining to nutrient requirements for working in hot environments and to comment on how this information might be applied to military nutrient standards and military rations. The committee was thus tasked with providing a thorough review of the literature in this area and with interpreting these diverse data in terms of military applications. In addition to a focus on specific nutrient needs in hot climates, the committee was asked to consider factors that might change food intake patterns and therefore overall calories. The CMNR was presented with this problem as a direct result of the movement of the Armed Forces into Saudi Arabia in Operation Desert Shield in the autumn of 1990; the committee was organizing the workshop that resulted in this report while the American Armed Forces were actively engaged in Operation Desert Storm in early 1991. Although concern for adequate nutrition for U.S. soldiers in Saudi Arabia prompted the initiation of this project, its scope was defined as including the nutrient needs of individuals who may be actively working in both hot-dry and hot-moist climates.



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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations 1 Introduction and Background THE COMMITTEE'S TASK The Committee on Military Nutrition Research (CMNR) of the Food and Nutrition Board (FNB), Institute of Medicine (IOM), National Academy of Sciences (NAS), was asked by the Division of Military Nutrition, U.S. Army Institute of Environmental Medicine (USARIEM), U.S. Army Medical Research and Development Command (USARMRDC), to review current research pertaining to nutrient requirements for working in hot environments and to comment on how this information might be applied to military nutrient standards and military rations. The committee was thus tasked with providing a thorough review of the literature in this area and with interpreting these diverse data in terms of military applications. In addition to a focus on specific nutrient needs in hot climates, the committee was asked to consider factors that might change food intake patterns and therefore overall calories. The CMNR was presented with this problem as a direct result of the movement of the Armed Forces into Saudi Arabia in Operation Desert Shield in the autumn of 1990; the committee was organizing the workshop that resulted in this report while the American Armed Forces were actively engaged in Operation Desert Storm in early 1991. Although concern for adequate nutrition for U.S. soldiers in Saudi Arabia prompted the initiation of this project, its scope was defined as including the nutrient needs of individuals who may be actively working in both hot-dry and hot-moist climates.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations The CMNR was asked to address the following questions: What is the evidence that there are any significant changes in nutrient requirements for work in a hot environment? If such evidence exists, do the current Military Recommended Dietary Allowances provide for these changes? Should changes be made in military rations that may be used in hot environments to meet the nutrient requirements of soldiers with sustained activity in such climates? Specifically, are the meals, ready-to-eat (MREs) good hot-weather rations? Should the fat content be lower? Should the carbohydrate content be higher? What factors may influence food intake in hot environments? To what extent does fluid intake influence food intake? Is there any scientific evidence that food preferences change in hot climates? Are there special nutritional concerns in desert environments in which the daily temperature may change dramatically? Is there an increased need for specific vitamins or minerals in the heat? Does working in a hot climate change an individual's absorptive or digestive capability? Does work at a moderate to heavy rate increase energy requirements in a hot environment to a greater extent than similar work in a temperate environment? To assist the CMNR in responding to these questions, a workshop was convened on April 11–12, 1991, that included presentations from individuals familiar with or having expertise in digestive physiology, energetics, macro-nutrients, vitamins, minerals, appetite, psychology, sociology, and olfaction. The invited speakers discussed their presentations with committee members at the workshop and submitted the content 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 workshop presentations and drew on its collective expertise and the scientific literature to develop the following summary, conclusions, and recommendations. MILITARY RECOMMENDED DIETARY ALLOWANCES History The history of the Military Recommended Dietary Allowances (MRDAs) is related to the history of both the Recommended Dietary Allowances (RDAs)

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations and the Food and Nutrition Board of the National Academy of Sciences. The Food and Nutrition Division, Office of the Surgeon General, U.S. Army, was established in 1917 to (1) safeguard the nutritional interests of the Army; (2) inspect food supplied to the Army to ensure the proper amount and distribution of nutrients; and (3) obtain data on which to base intelligent alterations of military rations. During World War I, the Food and Nutrition Division of the Army conducted nutrition surveys at Army training camps to determine food consumption and wastage. Based on these early surveys, the first recommended nutrient requirements for the training of soldiers were developed in 1919. They were listed as follows: protein, 12.5 percent kcal; fat, 25 percent kcal; and carbohydrate, 62.5 percent kcal (Murlin and Miller, 1919). During World War II the responsibilities for nutrition of the Office of the Surgeon General were expanded to provide more direct nutrition guidance. In 1940 the Food and Nutrition Board (FNB) of the National Academy of Sciences was organized in conjunction with the defense program to help the Army establish a satisfactory standard for operational rations. From 1943 until 1947 the Surgeon General's Office accepted diets as nutritionally adequate if they met the recommended allowances of the FNB. Beginning with Army Regulation (AR) 40-250 Nutrition (October 28, 1947), the Office of the Surgeon General initiated the first use of a specified ''Minimum Nutrient Intake'' for military personnel. These standards incorporated an adjusted caloric standard for the extreme cold. The military nutrient standards were patterned after the current FNB Recommended Dietary Allowances (RDAs) with modifications to meet the needs of Army personnel beginning with AR 4-564 (February 9, 1956). The first Tri-Service regulation (AR 40-25, 1968) based on the RDAs with modifications was issued on July 2, 1968. The military nutrition standards were first termed "Military Recommended Dietary Allowances" with the May 15, 1985, revision of AR 40-25. The CMNR provided commentary to the Army during the revision process. This regulation also designated the Army Surgeon General as the Department of Defense (DOD) Executive Agent for Nutrition for the military. The 1985 MRDAs are adapted from the ninth edition of the RDAs (NRC, 1980) and are the current standard for all branches of the military. Current MRDAs The MRDA regulation (AR 40-25, 1985) is presently under revision.1 The revised standards will reflect changes in the nutrition knowledge base, 1   At the request of the Army Medical Research and Development Command representative, the Committee on Military Nutrition Research held a meeting on November 27, 1990, at the

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations changes in the RDAs based on the tenth edition (NRC, 1989b), and military nutrition initiatives for the twenty-first century. AR 40-25 (1985) not only lists the nutrient standards but includes definitions of terminology, guidelines for healthful diets, and clarification of the use of the MRDAs for menu planning, dietary evaluations, nutrition education, and food research and development in the military. A separate table provides nutritional standards for operational and restricted rations. AR 40-25 is included in full in Appendix A. One purpose of the present study was to comment on the applicability of the current MRDAs for work in hot environments. Table 1-1 is a comparison of the nutrient recommendations in the latest edition of the RDAs (NRC, 1989b) and those in AR 40-25 (1985). Table 1-2 compares the estimated safe and adequate ranges for selected vitamins and minerals from the same two sources. These tables provide a reference for the physiological and nutrient-by-nutrient discussion that follows. PHYSIOLOGICAL CHANGES ARISING FROM EXERCISE AND HEAT For the most part, reported studies in the areas of physiology and gastrointestinal function have examined the effect on physiological function of an increased core temperature, whether as a result of exercise or increased ambient temperature. In only a few cases are the effects of exercise on body core temperature compared with the effects of a hot environment alone, whether in exercising or resting people. A few studies are described in the historical perspective in Chapter 6. Important physiological considerations related to performance are reviewed below. Exercise Muscular exercise can increase metabolism by up to 15 times the basal rate (see discussion in Chapter 3). Most of the heat resulting from this level of energy expenditure needs to be removed to maintain thermostasis. Heat loss occurs through both insensible (evaporative) and sensible (radiative and convective) mechanisms. These are controlled by a thermoregulatory center in the hypothalamus; this center, through the autonomic nervous system, controls heat transfer from the body core to the skin primarily via     National Academy of Sciences in Washington, D.C., to discuss the status and the direction of the revision of the MRDAs. Dietitians and representatives from the Army, Navy, Air Force, Marines, and Coast Guard attended and discussed specific service-based concerns regarding MRDA revisions and issues related to military nutrition initiatives for the future. They also covered garrison menu planning and general implementation of the MRDAs in various nongarrison military settings.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations blood circulation. The increased blood flow to the surface raises the temperature of the skin and allows sensible heat loss by radiative and convective mechanisms. Evaporative heat loss occurs through sweating (see Chapters 3, 4, and 5). Heavy exercise at increased ambient temperatures decreases the skin-to-ambient-temperature gradient, thus substantially decreasing sensible heat loss. Under these conditions, most heat loss by the body will occur through evaporative cooling (i.e., sweating). As is well known, heat loss by this mechanism can be greatly decreased under conditions of high humidity. The resulting dehydration from excess sweating can reduce blood volume and cardiac filling. If compensatory circulatory and cardiac changes are insufficient, skin and muscle blood flow will be impaired, thus reducing sensible heat loss and physical performance. A state of adequate hydration is therefore important in maintaining the effectiveness of the physiological mechanisms involved in heat dissipation. Heat Stress Thermoregulation can be defined as the summation of the mechanisms by which the body adapts to a heat stress in order to maintain thermoneutrality. Body core and skin temperatures have been used as indices of the ability of the body to thermoregulate, along with cardiovascular changes in heart rate, blood volume (see Harrison, 1985, for a comprehensive review) and blood pressure, with sweat rate as a visible mechanism of adaptation. Acclimatization is the process of adapting to prolonged exposure to a new environment, so that the mechanisms that result in initial responses are modified to allow increased endurance with less strain on body functions. The ability to defend one's body temperature against heat stress is influenced by level of activity, acclimatization state, aerobic fitness, and hydration level. In heat-acclimatized2 individuals, the thermoregulatory mechanisms involved in dissipating heat become fully operative. Although some investigators report that to perform a given submaximal exercise task the metabolic rate is greater in a hot compared to a temperate environment (Consolazio et al., 1961, 1963; Dimri et al., 1980, Fink et al., 1975), other investigators report lower metabolic rates in the heat (Brouha et al., 1960; Petersen and Vejby-Christensen, 1973; Williams et al., 1962; Young et al., 1985). A person's state of heat acclimatization does not account for whether individuals demonstrate an increased or decreased metabolic rate during submaximal exercise in the heat; other mechanisms explain this discrep- 2   The term heat acclimatization is used here to refer to the adaptive changes that occur due to exposure to a hot natural environment; heat acclimation will be used to refer to adaptive changes to a hot environment under controlled conditions, such as in an environmental chamber.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations TABLE 1-1 Comparison of the Current Military Recommended Dietary Allowances (MRDAs) (AR 25-40, 1985) That Are Based in Part on the Ninth Edition of the Recommended Dietary Allowances (RDAs) (NRC, 1980) with the Most Recent RDAs (NRC, 1989b)     MRDAsa RDAsb     Men Women Men Men Women Women Nutrient Unit (17–50 y) (17–50 y) (19–24 y) (25–50 y) (19–24 y) (25–50 y) Energy Kcal 3200 (2800–3600)c,d 2400 (2000–2800)c,d 2900e 2900e 2200e 2200e   MJ 13.4 (11.7–15.1) 10.0 (8.4–11.7)         Protein g 100f 80f 58 63 46 50 Vitamin Ag µg RE 1000 800 1000 1000 800 800 Vitamin Dh µg 5–10i 5–10i 10 5 10 5 Vitamin Ej mg TE 10 8 10 10 8 8 Ascorbic Acid mg 60 60 60 60 60 60 Thiamin (B1) mg 1.6 1.2 1.5 1.5 1.1 1.1 Riboflavin (B2) mg 1.9 1.4 1.7 1.7 1.3 1.3 Niacink mg NE 21 16 19 19 15 15 Vitamin B6 mg 2.2 2.0 2.0 2.0 1.6 1.6 Folacin µg 400 400 200 200 180 180 Vitamin B12 µg 3.0 3.0 2.0 2.0 2.0 2.0 Calcium mg 800–1200i 800–1200i 1200 800 1200 800 Phosphorus mg 800–1200i 800–1200i 1200 800 1200 800 Magnesium mg 350–400i 300i 350 350 280 280 Iron mg 10–18i 18i 10 10 15 15 Zinc mg 15 15 15 15 12 12 Iodine µg 150 150 150 150 150 150 Sodium mg See notel See notel 500m 500m 500m 500m

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations a MRDA for moderately active military personnel, ages 17 to 50 years, are based in part on the Recommended Dietary Allowances, ninth revised edition, 1980. The MRDAs are currently under revision. b For the RDAs, the allowances, expressed as average daily intakes over time, are intended to provide for individual variations among most normal persons as they live in the United States under usual environmental stresses. Diets should be based on a variety of common foods in order to provide other nutrients for which human requirements have been less well defined. See text for detailed discussion of allowances and of nutrients not tabulated. Values are taken from the RDAs, tenth edition (NRC, 1989b). c Energy allowance ranges are estimated to reflect the requirements of 70 percent of the moderately active military population. One megajoule (MJ) equals 239 kcal. d Dietary fat calories should not contribute more than 35 percent of total energy intake. e From Table 3–5 from the RDAs, tenth edition (NRC, 1989b) by using the assumption of light to moderate activity for each age and gender group. These figures were calculated using the World Health Organization (WHO, 1985) equations for resting energy expenditure multiplied by an activity factor as described in the text (NRC, 1989b) pp. 25–33. f Protein allowance is based on an estimated protein requirement of 0.8 g per kilogram (kg) desirable body weight. By using the reference body weight ranges for males of 60 to 79 kilograms and for females of 46 to 63 kilograms, the protein requirement is approximately 48 to 64 grams for males and 37 to 51 grams for females. These amounts have been approximately doubled to reflect the usual protein consumption levels of Americans and to enhance diet acceptability. g One microgram of retinol equivalent (µg RE) equals 1 microgram of retinol, or 6 micrograms beta-carotene, or 5 international units (IU). h As cholecalciferol, 10 micrograms of cholecalciferol equals 400 IU of vitamin D. i High values reflect greater vitamin D, calcium, phosphorus, magnesium, and iron requirements for 17-to 18-year olds than for older ages. j One milligram of alpha-tocopherol equivalent (mg TE) equals I milligram d-alpha-tocopherol. k One milligram of niacin equivalent (mg NE) equals I milligram niacin or 60 milligram dietary tryptophan. l The safe and adequate levels for dietary sodium intake of 1100 to 3300 mg published in the RDAs (NRC, 1980) are currently impractical and unattainable within military food service systems. However, an average of 1700 milligrams of sodium per 1000 kilocalories of food served is the target for military food service systems. This level equates to a daily sodium intake of approximately 5500 milligrams for males and 4100 milligrams for females. [Note: This comment is based on the ninth edition of the RDAs (NRC, 1980). The MRDAs are currently under revision in light of the 1989 publication of the tenth edition of the RDAs (NRC, 1989b).] m Estimated minimum requirements for healthy persons. No allowance has been included for large, prolonged losses from skin through sweat. There is no evidence that higher intakes confer any health benefit. SOURCE: Adapted from Table 2-1, MRDA for selected nutrients, p. 2-4 (AR 25-40, 1985) and National Research Council Recommended Dietary Allowances (1989b), p. 284, and Tables 3-4, 3-5, and 11-1; pp. 29, 33, and 253.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations TABLE 1-2 Comparison of the Estimated Safe and Adequate Daily Dietary Intake Ranges of Selected Vitamins and Minerals from the Military Recommended Dietary Allowances (AR 25–40, 1985) That Are Based in Part on the Ninth Edition of the Recommended Dietary Allowances (RDAs) (NRC, 1980) with the Values from the Tenth Edition of the RDAs (NRC, 1989b) Nutrient Unit From MRDAsa From RDAsb Vitamins Vitamin K µg 70–140 65, 80c Biotin µg 100–200 30–100 Pantothenic Acid mg 4–7 4–7 Trace Elementsd Fluoride mg 1.5–4.0 1.5–4.0 Selenium µg 50–200 55, 70c Molybdenum mg 0.15–0.50 0.075–0.250 Copper mg 2–3 1.5–3.0 Manganese mg 2.5–5.0 2.0–5.0 Chromium µg 50–200 50–200 Electrolytes Potassium mg 1875–5625 2000 Chloride mg 1700–5100 750 a MRDAs = Military Recommended Dietary Allowances. Data in this portion of the table are based in part on the Recommended Dietary Allowances , ninth edition, 1980, Table 10, "Estimated Safe and Adequate Daily Dietary Intakes of Selected Vitamins and Minerals." Estimated ranges are provided for these nutrients because sufficient information upon which to set a recommended allowance is not available. Values reflect a range of recommended intake over an extended period of time. b RDAs = Recommended Dietary Allowances. Because there is less information on which to base allowances, these figures were not given in the main table of RDA and were provided in the form of ranges of recommended intakes. c First number is the RDA for women aged 19–50; the second number is the RDA for men of the same age range. With the publication of the tenth edition of the RDAs, vitamin K and selenium were moved into the summary chart for recommended, age and gender-based dietary allowances. d Since the toxic levels for many trace elements may be only several times usual intakes, the upper levels for the trace elements given in this table should not be habitually exceeded. SOURCE: MRDA values adapted from Table 2-2, p. 2-5 (AR 40-25, 1985); RDA values adapted from Table 11-1, p. 253; Summary Table: Estimated Safe and Adequate Daily Dietary Intakes of Selected Vitamins and Minerals, p. 284, and the Recommended Dietary Allowances, tenth edition, 1989, Summary Table, p. 285 (NRC, 1989b).

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations ancy. Most investigators have only calculated the aerobic metabolic rate during submaximal exercise, ignoring the contribution of anaerobic metabolism to total metabolic rate. Although both increases and decreases have been observed in metabolic rate in the heat, it does not appear that the presence or absence of heat acclimatization has an effect on metabolic rate (see Chapters 3 and 6 for further discussion). Muscular activity produces an enormous amount of heat, with the amount of heat production directly related to the intensity of exercise (Nadel et al., 1977). The amount of heat production generated by the increased energy metabolism of skeletal muscle during exercise may be as much as 100 times that of inactive muscle. The mechanisms for dissipating this heat are generally well regulated. Although heat loss occurs through evaporation of sweat and by conduction; convection, and radiation, evaporation of sweat is clearly the most effective avenue of heat loss during exercise. The sweat glands are capable of secreting up to 30 grams of sweat per minute, removing approximately 18 kcal of heat in the process. Sweat rate is directly associated with exercise intensity (Maughan, 1985; Nadel et al., 1977). Gastrointestinal Functioning It has been reported (see Chapter 4) that gastric emptying and intestinal motility decrease as core temperature increases during exercise and in hypohydration. Some, but not all, investigators have also observed reductions in intestinal absorption of nutrients under these conditions. Most of the studies on the effects of exercise and heat on gastrointestinal function have been carried out in endurance athletes such as marathon runners. Gastrointestinal symptoms under these conditions are often severe, although transient. They include cramps, belching, gastrointestinal reflux, flatulence, bloody stools, vomiting, diarrhea, and nausea. Mechanisms for these effects are discussed in Chapter 4. The relevance of these findings to the range of physical activity in the military is not at all clear, and the findings appear transient when associated with extreme physical activity. Instances of levels of physical activity in the military approaching those of highly competitive endurance athletes would appear to be the exception rather than the rule. CHANGES IN NUTRIENT REQUIREMENTS FOR HOT ENVIRONMENTS Fluid and Dehydration The requirement for water in a hot environment depends on the amount of fluid loss, which in turn depends on such factors as exercise intensity,

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations exercise duration, environmental conditions (dry heat versus humid heat), state of training and heat acclimatization, sex, and age (see Chapter 5). The increased heat production of exercise, an increased sweat rate, and inadequate hydration predispose soldiers in hot environments to dehydration. Along with exercise intensity, sweat rate is related to environmental conditions, clothing, and acclimatization state (Shapiro et al., 1982). In hot, dry conditions, water loss from the skin and respiratory surfaces can be as much as 2 to 3 liters per hour (Wenger, 1988). In hot, moist (humid) conditions, sweat losses are measurably less than in hot, dry conditions. In a study that measured physiologic changes and sweat losses in healthy young men during hyperthermia induced by humid heat in an environmental chamber, total sweat losses averaged 7 liters per 24 hours (Beisel et al., 1968). However, humidity per se does not appear to affect core (rectal) temperature (Morimoto, 1967). In terms of military apparel, the nuclear-biological-chemical (NBC) protective clothing worn by many military personnel prevents the normal dissipation of body heat because of the cloth's lack of moisture permeability and its insulating properties. As a result, body temperature may rise excessively, producing high levels of sweat (1 to 2 liters per hour) that cannot evaporate effectively because air turnover is reduced, and caution must be taken (Muza et al., 1988; Pimental et al., 1987). If the fluid involved in excessive sweat loss is not replaced, total body water, along with the total blood volume, will be decreased. A water loss as small as 1 percent of body weight will induce changes such as increased heart rate during rest and exercise, and decreased performance. However, a 1 percent loss is difficult to discern relative to what might be regarded as initial water balance. Thus, it is hard to attribute physiological changes to a 1 percent loss, but such changes can be readily observed at losses of 2.0 to 2.5 percent. A 10 percent loss of body weight through dehydration3 is life-threatening (Adolph, 1947). Water loss from the blood leads to a decrease in sweat rates and skin blood flow (Sawka and Pandolph, 1990; Wyndham, 1977), which results in less evaporative cooling and a risk of heat stroke (Wyndham, 1977). The normal compensatory response to exercise and heat stress is increased peripheral blood flow to maximize heat dissipation and prevent hyperthermia. However, in dehydrated individuals with greatly diminished blood volume, skin blood flow is reduced to maintain cardiac output and blood pressure. Reductions in blood volume can result in a reduced flow of blood to organs during exercise and reduced venous flow in return. This reduced venous return to the heart decreases stroke volume and causes a compensatory increase in the heart rate to maintain cardiac output and blood pressure. 3   The term dehydration is used here to refer to the process of losing body water, while the term hypohydration will be used to denote the result of the dehydration process.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations This reflex increase in heart rate, however, is not sufficient to compensate for the decrease in stroke volume (Rowell et al., 1966); consequently, maximal cardiac output is reduced. Several studies have shown that cardiovascular performance is compromised following thermal or exercise-induced hypohydration ≤(2 percent body weight loss) (Armstrong et al., 1985; Costill et al., 1976; Pitts et al., 1944; Saltin, 1964). Cardiac output is reduced by almost 2 liters per minute with decreased blood volume (Fortney et al., 1983; Nadel et al., 1980). This reduction in cardiac output can almost entirely account for decreases in as a result of hypohydration (Rowell et al., 1966; Saltin, 1964). Significant reductions in physical work capacity have been seen in wrestlers after hypohydration-caused weight loss (Herbert and Ribisl, 1972), as well as in runners after diuretic-induced weight loss (Armstrong et al., 1986). The acute heat stress in hot climates that causes and is caused by dehydration has been associated with several factors. It can be precipitated by an increase in resting and submaximal exercise metabolic rates (Consolazio et al., 1961, 1963; Dimri et al., 1980; Fink et al., 1975), increases in plasma or muscle lactate levels (Dill et al., 1930; Dimri et al., 1980; Fink et al., 1975; Nadel, 1983; Robinson et al., 1941; Young et al., 1985), and glycogenolysis during submaximal exercise. Effect of Gender Early studies that investigated dehydration and exercise in heat and humidity found differences in sweat rate and endurance, with women sweating less than men for a given thermal stress (Fox et al., 1969; Wyndham, 1965). These studies were initially interpreted as evidence that women were not as capable as men in coping with heat stress. More recent studies comparing the effects of exercising in heat and humidity in men and women continue to find differences in sweat rate. Gender differences in response to thermal stress (body core temperature, acclimatization, etc.) however, appear to result from differences in aerobic power, due to disparities in body weight-to-mass ratio or level of physical fitness (Armstrong et al., 1990; Avellini et al., 1980; Dill et al., 1977; Grucza et al., 1985; Havenith and van Middendorp, 1990; O'Toole, 1989; Paolone et al., 1978; White et al., 1992; Chapter 5, this volume). Avellini et al. (1980) compared acclimation to work in humid heat in an environmental chamber in men and women with similar aerobic capacities and surface-area-to-mass ratios. The women were tested both pre-and postovulation. Prior to acclimation, the women sweated less than the men, their endurance was greater, and their rectal temperature and heart rate did not increase to the level seen in men. After acclimation, rectal temperature and heart rates were similar, although there was an increased difference in sweat

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations ing the day for the same individual. Some soldiers also reported self-medication to prevent defecation while on 3-to 4-day missions. Food Preferences As might be expected, foods that were commercially labeled—even though they were not as heat stable and in certain cases showed evidence of some deterioration—were preferred to the field ration (MRE). Apparently, soldiers had greater confidence—in terms of meeting their appetite and nutritional needs—in foods that seemed to be the same (including packaging) as those they had consumed at home. This was particularly true for flavored beverage powder. A significant concern of soldiers was the compatibility of foods in each MRE. For example, an MRE that contained a slice of ham as an entree did not come with cheese, which would have been preferable for making a sandwich. It instead was packaged with peanut butter. Likewise, peanut butter and jelly were not packed together in any MRE pouch because they were both considered "spreads." To overcome this problem, soldiers would "rob" one MRE pouch to obtain the other spread and then discard the remaining contents. Because the Desert Shield operation lasted from summer to winter, it was necessary to provide foods appropriate to the prevailing climatic conditions. In the summer, the amount of beverage bases provided in each MRE pouch was not adequate to flavor all the water that was consumed. (Soldiers deemed it necessary to flavor the water because of its unpalatability.) Individuals were drinking from 8 to 9 bottles per day; thus, three beverage bases were needed to flavor 1 1/2 liters of water per bottle. Likewise, during the colder season, the soldiers all wanted cocoa, which had been discarded during the summer. Because cocoa was not included in every MRE pouch, often a hot drink choice was not available with each meal. Concomitantly, in order to have a hot drink, soldiers in the field who did not have access to kerosene heaters needed hot tabs.6 This had a direct effect on the acceptability of the rations. In 130°F weather, soldiers did not want a hot meal but rather the MRE entrees that were intended to be eaten without heating. In essence, they would have preferred entrees that were cool or cold. Social/Psychological Aspects of Eating The use of individual MREs decreased socialization because there was no need for a field kitchen and a common mess. To soldiers with little access to information about what was going on in the war, this practice 6   Hot tabs are small portable elements for warming ration components. They are included only with rations that require heating.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations decreased morale, because the opportunity for bringing the unit together on at least a daily basis was not available. Thus, the use of MREs, in decreasing social interaction, acted as a psychological stressor. Caffeine consumption changed dramatically depending on the situation of the troops, and the use of smokeless tobacco increased as a result of light (fire) discipline and the fire hazards associated with smoking. It was reported by the two observers that these changes affected eating patterns but no quantitative information was available. In addition, the use of meal shifts changed normal times of meals and the types of food associated with certain meals, as well as the desire, among some soldiers, to have a meal. Nutrition Understanding The observations presented concerning Desert Shield and Desert Storm reinforced the committee's belief that a broad program of educating soldiers with regard to the ration and its contents, and how it would influence their desire to maintain or change body weight, was needed on the unit level. Many soldiers apparently read the packaging labels on their foods; this could be a vehicle for additional information and education. It may be appropriate to determine the need, if any, for a general policy regarding vitamin and mineral supplementation. Many soldiers reported their consumption of supplements from personal supplies or packages that were requested from home. The CMNR recommended in an earlier review of the MREs and T rations (NRC, 1986) that the distribution of vitamin and mineral supplements was unnecessary and ill-advised if the rations were well fortified by meeting the MRDAs and if the soldiers ate the rations in sufficient quantities to meet their caloric needs. Summary The following recommendations, gleaned from anecdotal comments of soldiers in the field during Operations Desert Shield and Storm, were discussed informally at the workshop: (1) pouch bread should be available at every meal, if at all possible; (2) more eat-on-the-go-type foods are necessary, such as cookie bars or snack items that could be saved and eaten later; (3) food items within the individual MREs should be packaged together so that they form complementary alternative foods, such as sandwich ingredients; (4) although salt packets are rarely used, other condiment packets such as pepper or mustard should be provided to add variety to the meal; (5) MREs should be unitized, along with sundry packs, supplement packs, and other such items, so that each pallet has a variety when it is moved forward to the field of operation. Although, it must be recognized that the decision to fortify certain foods within the MRE places the onus on the soldier to eat

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations that specific item in order to meet the MRDA, practice in the field indicates that this was not always achieved. CONCLUSION The magnitude of the stress imposed by exercise in hot environments depends on an individual's nutritional status and his or her ability to regulate metabolic events and dissipate heat. Increased heat production, increased sweat losses, and inadequate hydration predispose soldiers in hot environments to dehydration. It is of paramount importance that hydration be preserved to maintain performance. Although it is generally recognized that some losses of minerals and vitamins occur during intense exercise in hot environments, available information suggests that the present MRDAs are adequate for achieving optimal work performance and preventing overt clinical deficiencies. The absence of sensitive, reliable indicators of many nutritional inadequacies limits the detection of subtle changes in dietary practices on health and performance. The interrelationships of exercise in hot environments and nutrient requirements, as influenced by eating behavior, age, gender, and body composition, are unclear. These factors clearly deserve additional investigation. There is substantial evidence that food intake decreases markedly as the environmental temperature increases, which probably reflects the need to control thermogenesis. It thus becomes prudent to provide palatable, nutrient-rich foods that reduce the monotony of eating during extremely hot conditions. Quoting E. R. Buskirk (Chapter 6): ''Finally, as the nutritional situation during the recent operations of Desert Shield and Desert Storm is reviewed, a comment by R. M. Kark (1954) comes to mind: 'Field studies have shown that physical deterioration in soldiers may be due to inadequate nutrition, but perhaps what is more important, they have shown that loss of military efficiency through inadequate nutrition is most often due to inadequate planning, catering or supply, and to inadequate training or indoctrination.... Maintaining good nutrition is like maintaining freedom of speech or democracy. You need eternal vigilance to make it work.''' REFERENCES Adolph, E.I. 1947 Physiology of Man in the Desert. New York, N.Y.: Interscience. Aidasher, A.A., B.I. Kim, O.A. Kolesova, V.L. Reznik, and V.V. Subach 1986 Indices of the nutritional status of workers in the oil and gas production industry adapting to the extreme conditions of an arid zone. (in Russian) Vopr. Pitan. May–June (3):25–28. Andersson, B., and B. Larsson 1961 Influence of local temperature changes in the preoptic area and rostral hypothalamus on the regulation of food and water intake. Acta Physiol. Scand. 52:75–89.

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