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6
Energetics and Climate with Emphasis on Heat: A Historical Perspective

Elsworth R. Buskirk1

INTRODUCTION

This historical review presents some considerations for supplying military personnel with appropriate nutrition as they operate in different climates. Attention is paid to some of the pertinent investigations undertaken related to energy turnover in the 1930s through the 1960s, with a few comments regarding interpretation of results based on more current knowledge.

EARLY APPRAISALS

Many of the earlier appraisals of the nutritional needs of U.S. Armed Forces personnel were published as reports of the various agencies involved. For the purposes of this presentation, the following agencies are identified:

  • Quartermaster Food and Container Institute for the Armed Forces, Chicago, Illinois

  • U.S. Army Medical Research and Nutrition Laboratory, Fitzsimmons General Hospital, Denver, Colorado

  • Aero Medical Laboratory, Wright Air Development Center, United States Air Force, Wright Patterson Air Force Base, Ohio

1  

Elsworth R. Buskirk, Noll Laboratory for Human Performance Research, College of Health and Human Development, The Pennsylvania State University, University Park, PA 16802



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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations 6 Energetics and Climate with Emphasis on Heat: A Historical Perspective Elsworth R. Buskirk1 INTRODUCTION This historical review presents some considerations for supplying military personnel with appropriate nutrition as they operate in different climates. Attention is paid to some of the pertinent investigations undertaken related to energy turnover in the 1930s through the 1960s, with a few comments regarding interpretation of results based on more current knowledge. EARLY APPRAISALS Many of the earlier appraisals of the nutritional needs of U.S. Armed Forces personnel were published as reports of the various agencies involved. For the purposes of this presentation, the following agencies are identified: Quartermaster Food and Container Institute for the Armed Forces, Chicago, Illinois U.S. Army Medical Research and Nutrition Laboratory, Fitzsimmons General Hospital, Denver, Colorado Aero Medical Laboratory, Wright Air Development Center, United States Air Force, Wright Patterson Air Force Base, Ohio 1   Elsworth R. Buskirk, Noll Laboratory for Human Performance Research, College of Health and Human Development, The Pennsylvania State University, University Park, PA 16802

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations TABLE 6-1 Environmental Temperature, Physical Fitness, and Calculated Average Nutrient Intake, U.S. Troops in Pacific Compared with U.S. Troops in North America Information Hawaii Guadalcanal Guam Iwo Jima 38th Division, Luzon Infantry Battalion, Colorado Training Camps, U.S.* Mean temperature, °F +72 +85 +81 +78 +83 +65 Various Score in fitness test 55 57 70 76 81 71 nd Nutrient intake, average per man per day Kcal per day 3400 3400 3500 3500 3200 3900 3790 Carbohydrate, g 460 450 480 470 430 520 408 Fat, g 124 129 124 129 120 147 178 Protein, g total 110 110 115 115 100 125 125 Protein, g animal 68 65 68 65 58 74 nd * nd = data not available. SOURCE: Adapted from Johnson and Kark (1946) based on original data from Howe and Berryman (1945) on 455 messes in U.S. training camps, 1941–1943.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations U.S. Army Medical Research Laboratory, Office of the Surgeon General, Fort Knox, Kentucky Quartermaster Climatic Research Laboratory, United States Army, Lawrence, Massachusetts U.S. Army Quartermaster Research and Development Center, United States Army, Natick, Massachusetts U.S. Army Research Institute of Environmental Medicine, United States Army, Natick, Massachusetts Those interested in perusing the various investigations conducted by personnel from these agencies should consult their respective report series because not all summaries of the sponsored work have appeared in the open scientific literature. It is hoped that many of the reports remain on file. Between 1941 and 1946, reliable data were collected of food intakes for physically fit, active ground troops who chose their foodstuffs from the rations provided in temperate, mountain, desert, jungle, arctic, and subarctic areas in North America, Europe, and Asia. Dietary surveys and Army ration trials had been conducted intermittently throughout World War II. Johnson and Kark (1947) summarized these data and presented a brief critical review of the nutrition of U.S. and Canadian soldiers in 1946 based on their more comprehensive report prepared for the U.S. Army's Quartermaster Food and Container Institute for the Armed Forces (Johnson and Kark, 1946). Their summarized nutrient intake data from several studies appear in Table 6-1. A somewhat abbreviated table was subsequently published in 1947 (Johnson and Kark, 1947) (Table 6-2). They clearly demonstrated the inverse relationship of caloric intake with mean local temperature as ascertained from the dietary surveys and ration trials. Groups of from 50 to 200 men were represented in each study. A consistent reduction in voluntary kcal intake per °F over the range-20° to 100°F was found. Their regression equation was: kcal per day = 4660-15.9 T (°F) where T is the mean external temperature. The higher the mean environmental temperature the lower the voluntary kcal intake, and the lower the mean environmental temperature the higher the voluntary kcal intake. Johnson and Kark (1947) concluded that the large difference in caloric intake could not be explained by differences in basal metabolic rate (a difference of 10 to 20 percent at most), body weight, or type of activity because they contended the ground troops carried out similar tasks in each environment. Unfortunately, they had little data to confirm no differences in physical activity by the troops at the several garrisons. Nevertheless, Johnson and Kark stated that the caloric expenditure for a given task was greater in the cold than in warm climates because of the ''hobbling effect'' of arctic clothing and equipment. They also concluded that more body heat

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations TABLE 6-2 Body Weight; Kcal Consumption; and Ratio of Protein, Fat, and Carbohydrate Eaten by Representative Groups of Ground Troops in Different Environments     Mean Body Average Kcal Intake Percentage of Kcal Provided by: Place and Troops Environment Weight (kg) per Man per Day Protein Fat Carbohydrate Canada, mobile force "Musk Ox" Arctic and subarctic 73.0 4400 11 40 49 U.S.A., ground troops Temperate 69.0 3800 13 43 44 Colorado Rockies infantry, Temperate mountain (9000 feet) 69.5 3900 13 34 53 Pacific Islands ground troops, Tropics 70.0 3400 13 33 54 Luzon, infantry Tropics 65.5 3200 12 34 54   SOURCE: Adapted from Johnson and Kark (1947).

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations was required in cold than in warm environments to maintain thermal balance. A review of Johnson and Kark's additional table clearly shows that the percentage of protein voluntarily chosen was essentially the same in each environment (Table 6-3). Percent fat intake in the warm environments was somewhat less than that in the cold and percent carbohydrate intake somewhat higher. Johnson and Kark's overall conclusion in regard to rations was that essentially the same rations can be supplied regardless of environment, but the colder the environment the more calories are needed. In addition, they emphasized that caloric requirements are in large measure determined by the physical activity in which troops are engaged and that their summary should be regarded as the setting of standards for dietary allowances. The conclusions of Johnson and Kark, for the most part, appear to be as valid today as when presented in the 1940s. Nutritional knowledge has advanced, food supplies—including military rations—have changed, but many of the tasks required of armed forces personnel still require physical effort, which is the major factor associated with differences in caloric needs. Of consequence, however, is that clothing has been improved, providing better protection in the cold and better potential for allowing heat loss in hot environments. Clothing items are also generally lighter in weight, and various vehicles have somewhat diminished personal load carrying. As a follow-up to the across-climate comparisons of Johnson and Kark, Quartermaster Research and Development Command and Medical Nutrition Laboratory personnel collaborated on a series of studies in desert, temperate, and arctic environments (Buskirk et al., 1956; Iampietro et al., 1956; Welch et al., 1957a,b, 1958). Caloric intake decreased as ambient temperature decreased, but the regression slope was considerably less than that of Johnson and Kark, when either moderate or relatively heavy work was performed. In fact, the regression slope was also considerably less than that emphasized in 1950 by the Committee of Caloric Requirements of the Food and Agricultural Organization (FAO) of the United Nations (1950): The existence of an approximately linear relationship between calorie expenditure and mean annual external temperature was assumed. It is recommended tentatively that for every 10° departure in mean annual temperature from the reference temperature of 10°C, requirements should be adjusted by 5 percent of requirements at the reference level, the 5 percent being subtracted for higher temperatures and added for lower temperatures. The regressions found in the collaborative study were approximately 4 kcal per °C for both moderate and relatively heavy work. The comparative slopes for FAO were approximately 15 kcal per °C and for Johnson and Kark were 30 kcal per °C. Of interest was that kcal intake was essentially

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations TABLE 6-3 Voluntary Average Nutrient Intake of North American Ground Troops Who Remained Healthy, Fit, and Efficient in Different Environments Information U.S. Training Camps Camp Carson Trials Exercise "Musk Ox" Guam Garrison Luzon 38th Infantry Division Type of troops All Infantry Motorized Garrison Combat Type of ration U.S. garrison U.S. B supplemented Canadian arctic U.S. B supplemented U.S. New C Duration of time on ration, weeks Indefinite 8 12 Indefinite 12 Environment Temperate Mountain, summer Arctic, winter Moist tropics Moist tropics Average intake per man per day kcal 3800 3900 4400 3500 3200 protein, g total 125 125 120 115 100 protein, g animal nd* 75 70 70 60 fat, g 180 145 190 125 120 carbohydrate, g 410 520 520 480 430 percent kcal 43 34 40 32 34 percent kcal, carbohydrate 44 53 49 55 54 percent kcal, protein 13 13 11 13 12 * nd = data not available. SOURCE: Adapted from Johnson and Kark (1946).

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations the same in all climates when calculated on the basis of body weight plus clothing and equipment weight manually transported. A kcal intake of 47 to 49 kcal per kg per day was found for moderate work in the three climates. During relatively heavy work, kcal intake increased from 60 to 62 kcal per kg per day (Welch et al., 1958). They concluded that the differences in energy expenditure among environments are largely accounted for by differences in body weight plus weight of clothing and equipment carried during the performance of duties in the respective environments. A recent field study showed that troops operating in a warm environment and performing moderate work loads consumed an average of between 44.3 and 47.2 kcal per kg per day (Rose and Carlson, 1986), values that agree with those found by Welch et al. (1958). ENERGY EXPENDITURE: SUBMAXIMAL EXERCISE An issue that has been investigated over the years with mixed results is the impact of heat on metabolic rate, both during rest and during exercise. A variety of hypothesized causes for different responses of the metabolic rate to exercise in the heat have been proposed and are listed in Table 6-4. The case for a relatively elevated metabolic rate was put forth by Consolazio et al. (1961, 1963, 1970) (Tables 6-5 and 6-6). The primary explanation of the relatively higher energy expenditure in hot compared to cooler environments was the energy expenditure associated with the production and secretion of sweat. Consolazio et al. expanded on the observations of Dill et al. (1931) and Welch et al. (1958). Results from the latter study appear in Table 6-7. Although the differences across climates and locations in the TABLE 6-4 Differences Among Studies: Hypothesized Causes of Different Responses in Metabolic Rate to Exercise in the Heat Physical condition of subjects Extent of heat acclimatization Skill Duration of exercise Exercise intensity Environmental heat stress Type Intensity Hydration state Febrile state Clothing worn Equipment carried

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations TABLE 6-5 Mean Oxygen Uptake during Rest, Moderate Activity, and Heavy Activity by Young Men (n = 7) in a Room Maintained at Different Temperatures   Mean Oxygen Uptake (ml per minute) Intensity of Activity 21.1°C (70°F) 29.4°C (85°F) 37.7°C (100°F) Percent Rest 273 282 304* 11.4 Moderate† 521 525 590* 13.3 Heavy‡ 1422 1404 1570* 11.7 * p ≤ 0.05, i.e., effect of 100°F > 85°F or 70°F. † Fifty minutes on cycle ergometer. ‡ Fifty minutes on cycle ergometer at 120 watts. SOURCE: Adapted from Consolazio et al. (1963). study by Welch et al. were nonsignificant, there appeared to be a trend for a higher energy expenditure during walking in a hot desert environment when expressed either as kcal per hour or kcal per kg per hour, where kg represents total weight transported. However, more recent studies have failed to find significant differences (Klausen et al., 1967; Rowell et al., 1969; Sen Gupta et al., 1977; Shvartz et al., 1977; Young et al., 1985). Shvartz et al. (1977) clearly indicated little difference in metabolic rate with ergometer exercise prior to heat acclimation (see Table 6-8). Sen Gupta et al. (1977) raised the possibility that although total energy expenditure during submaximal exercise was not different when the exercise was TABLE 6-6 Oxygen Uptake by Young Men (n = 7) Performing Different Types of Exercise* in a Desert Environment, Yuma, Arizona   Oxygen Uptake (ml per minute) Exercise Type Sun (37.8°C) Shade (37.8°C) Indoors (26°C) Bicycle 1 754† 683† 641 Bicycle 2 813† 751† 681 Treadmill 1156 1197† 1110 Resting 340† 322 314 * Two separate cycle ergometer rides that are indicated here as bicycle 1 and 2. † p < 0.05. SOURCE: Adapted from Consolazio et al. (1970).

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations TABLE 6-7 Partition of Energy Expenditure in Three Climates in 1955   Climate Task Cold, Ft. Churchill Canada (-22.5°F) Temperate, Natick Massachusetts (72°F) Hot, Yuma Arizona (90.5°)   8* 8* 11* Walking (3.41 mph, level terrain) kcal per hour 413 318 350 kcal per kg per hour† 4.82 5.12 5.26 Resting and sedentary activity, kcal × kg0.7 per hour‡ 4.58 4.62 4.40 * Number of subjects. † Body weight plus weight of clothing. ‡ Includes dietary-induced thermogenesis. SOURCE: Adapted from Welch et al. (1958). conducted in a hot or comfortable environment, the partitioning of energy expenditure was different, that is, less aerobic expenditure and greater anaerobic expenditure in the hot environment (Table 6-9). The results were subsequently confirmed by Dimri et al. (1980). The hypothesized explanation for this partitioning was the diversion of a significant amount of blood from the muscles to the skin for thermoregulation in hot environments. Although TABLE 6-8 Mean Oxygen Uptake Responses to Exercise Before (B) and After (A) 8 Days of Heat Acclimation   Mean Oxygen Uptake (ml per m2 per minute)   41W, 23°C 82W, 23°C 41W, 39.4°C Group B A B A B A Trained (n = 7) 623 570* 1075 960* 634 569* Untrained (n = 7) 668 577* 1061 985* 680 586* Unfit (n = 7) 615 531* 1050 932* 618 520* Control (n = 5) 625 578 1068 1030 611 615 NOTE: Heat acclimation regimen = 3 hours of exercise per day at 41 watts, Tdb = 39.4°C, Twb = 30.3°C, where Tdb = dry-bulb temperature and Twb = wet-bulb temperature. * p ≤ 0.05. SOURCE: Adapted from Shvartz et al. (1977).

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations TABLE 6-9 Mean Changes in Aerobic-Anaerobic Fractions of Oxygen Utilization During Fixed Submaximal Exercise for 5 Minutes in Comfortable and Hot Conditions   Mean Change in O2 Utilization (± SD)   Comfortable Environment (Tdb 29.0°C, Twb 21.3°C) Very Hot Environment (Tdb 36.5°C, Twb 28.5°C) Level of Significance Total (liters) 7.60 ± 1.21 8.06 ± 0.87 n.s. Aerobic (liters) 5.60 ± 6.50 5.27 ± 0.68 p < 0.05 Percentage of total 73.97 ± 6.50 65.40 ± 2.99 p < 0.02 Anaerobic (liters) 2.00 ± 0.62 2.78 ± 0.33 p < 0.01 Percentage of total 26.03 ± 6.50 34.60 ± 2.99 p < 0.02 NOTE: Exercise intensity = 600 kg per min, cycle ergometer; Tdb = dry-bulb temperature; Twb = wet-bulb temperature. SOURCE: Adapted from Sen Gupta (1977). this hypothesis might apply to short periods of exercise such as the 5-minute bouts used by Sen Gupta et al. (1977), it would undoubtedly not apply to longer bouts of exercise, for example, 1 to 8 hours or more when a balance in muscle and skin blood flow would be necessary to sustain the exercise. A relatively elevated anaerobic metabolism and higher blood lactate concentrations would not be present. Thus, the conclusion of Sen Gupta et al. "that during submaximal work in heat, the metabolism becomes more anaerobic and there is reduction in in submaximal and maximal workloads as the heat stress increases" must be qualified at least with respect to duration of submaximal exercise. Overall, whether energy expenditure is modified during exercise in the heat depends on the circumstances and conditions. Brief intense exercise in a hot environment may elevate energy expenditure by evoking anaerobic processes, but the increment in daily energy expenditure is likely to be negligible. Thus, the earlier investigators posed the problem, but in terms of meeting the daily kcal needs of troops working in a hot environment, the submaximal exercise they perform has no greater impact than if they performed the same tasks in a more comfortable environment. The possible reasons for either an increase or a decrease in metabolic rate in hot environments are listed in Tables 6-10 and 6-11. A careful appraisal of each military situation would reveal which factors are most important to consider while also bearing in mind the possible causes of different responses previously set forth in Table 6-4.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations TABLE 6-10 Possible Reasons for an Increase in Metabolic Rate in Hot Environments Lack of acclimatization Inefficient physical activity, psychomotor stress Q10 effect, elevated body temperature Greater sweat gland activity Tachycardia Increased pulmonary ventilation Increased anaerobic metabolism Increased RQ Increased O2 debt Increased lactate Increased muscle glycogen utilization Increased blood glucose utilization Lessened skeletal muscle blood flow NOTE: Q10 = adjustment in metabolic rate in relation to temperature change; RQ = respiratory quotient. TABLE 6-11 Possible Factors That Would Tend to Reduce Metabolic Rate in Hot Environments Complete acclimatization Lower basal metabolic rate Reduced physical activity, particularly intense activity Lighter-weight clothing Decreased appetite and associated dietary-induced thermogenesis ACCLIMATIZATION/ACCLIMATION A finding that has been repeatedly documented is that unacclimatized personnel suffer the consequences when suddenly exposed to stressful environments, whether the environmental stress is heat, cold, or altitude. The psychological and physical stresses associated with combat only complicate the adverse situation. At issue is inadequate acclimatization, which with sudden exposure to heat, not only perpetrates physiological strain but lessens initiative and appetite, which negatively affects nutritional status including water balance. The acclimatization process with exposure to hot environments proceeds rapidly, being virtually complete in the working soldier within 10 days (Adolph, 1947; Buskirk and Bass, 1957; Dill, 1938). During this time, body weight is invariably lost due to undernutrition, but the weight may be subsequently regained in toto or in part. Johnson (1946), in his review, concluded that following acclimatization, dietary require-

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations ments are qualitatively similar in hot and temperate areas but may remain quantitatively lessened in tropical climates by the sustained high loss of sweat and anorexia. The question of whether heat acclimatization (outdoors or in the field) or acclimation (indoors or in laboratories) has an effect on metabolic rate during rest and exercise has been studied intensively with mixed results. Some pertinent studies are cited from among the many in the literature. Robinson et al. (1945) and Eichna et al. (1950) found that heat acclimation lowered the metabolic rate associated with exercise in the heat by 4 to 8 percent. Shvartz et al. (1977) studied, using cycle ergometry, several groups of men who varied widely in physical fitness and were exposed to 8 days of heat acclimation. Despite interindividual differences in physical fitness, the postacclimation oxygen uptakes were invariably slightly less in all of the environments studied including a 39.4°C (103°F) environment (see Table 6-8). Sawka et al. (1983) reevaluated the problem. They concluded that heat acclimation, if it had an effect at all, slightly lowered metabolism associated with performance of exercise in the heat. The conclusion was based not only on their studies of 42 subjects of both genders, but on a review of the literature as well. Young et al. (1985) arrived at essentially the same conclusion (see Table 6-12). Presumably, the small reduction in metabolism is caused by the lesser respiratory and cardiac work caused by more efficient evaporative cooling, peripheral circulation, regulation, and the lowering of body temperature, although as Sawka et al. (1983) have pointed out, the role of such factors is TABLE 6-12 Statistical Analysis for Comparison of Main Effects of Heat Acclimation and Environment on Respiratory Measurements of Young Men (n = 13) Variable Acclimation Environment , liters per minute Pre > post* Cool > hot* RER† Pre > post* Cool < hot*   NS Cool < hot* NOTE: Environments: Cool—21°C, 30 percent relative humidity; hot—49°C, 20 percent relative humidity. Exercise: 30 minutes of cycle ergometry at 70 percent ; NS = not significant. * p ≤ 0.05 † RER = respiratory exchange ratio. SOURCE: Adapted from Young et al. (1985).

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations not clear-cut. They suggested further research to investigate the possible role of modification of motor unit recruitment patterns and muscular efficiency—the latter related to phosphorylation efficiency and contractile-coupling efficiency. Heat acclimatization/acclimation is a valuable physiological adaptation, but the process plays only a minor role in modifying energy turnover and caloric requirements. APPETITE Appetite tends to be adversely affected among unacclimatized personnel who are abruptly exposed to a hot environment, a finding that has been recognized for some time. Taylor in 1946, quoted by Mitchell and Edman (1951), suggested the following: Hot weather presents no particular problems other than taste, custom and supply. Palatability is essential to combat the prevalent anorexia as assurance of good nutrition. Kark et al. (1947) recommended maintaining appetite through variety, familiarity, and high quality. In providing rations for soldiers at least three considerations are of prime importance. First, a considerable variety of food items should be issued. Second, the food items should be much the same as soldiers are accustomed to in ordinary life, but emphasis should be placed on acceptable foods of high biological value. Third, caloric deficits must be avoided. Although appetite, hunger, and satiety are complex processes, they must be addressed with regard to hot environments. Hard work in the heat, particularly for the unacclimatized, challenges ration providers and food preparers to offer in sufficient quantity safe, appealing food of good nutritional quality. RESTING METABOLISM/DIETARY-INDUCED THERMOGENESIS One of the thoughts perpetuated in the 1930s through the 1950s was that the specific dynamic action (SDA) of foods—now commonly identified as the thermic effect of food or dietary-induced thermogenesis—contributed significantly to daily kcal turnover. Swift and French (1954) reviewed the various studies and concluded that the impact of specific dynamic effect (SDE) was overemphasized, but that it remained a significant minor factor, in the range of 2 to 8 percent of ingested energy. When people consume mixed meals, the relative SDE impact of protein, carbohydrate, or fat becomes indistinguishable. In an early evaluation of basal metabolism in the tropics, MacGregor

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations and Loh (1941) showed that basil metabolic rate (BMR) declined in certain normal individuals, but not in others. The depression in BMR in those affected appeared to reach a maximum before the end of the first year of residence and was maintained after 2 years in the tropics. Military training for 3 months in the same environment appeared to have no influence on the interindividual patterns of response. Neither alterations in diet nor weight loss accounted for the interindividual differences. The authors concluded that the continued relatively high temperatures and possibly humidities were responsible for the depression of BMR in those susceptible. The environmental conditions in Singapore where the work was done averaged 28.3°C (83°F) during the day and 24.4°C (76°F) at night with frequent high humidity. Others have also reported an impact of environmental temperature on BMR or resting metabolism (for example, Galvao, 1950; Mason, 1934). To further such observations, an experiment was designed to evaluate the changes in resting metabolism during the day when food and exercise are taken as usual (Buskirk et al., 1957). Comparisons were made across climates varying from a cold (arctic) to a hot (desert) environment. It was concluded that specific dynamic action or dietary-induced thermogenesis assessed by periodic measurements of oxygen consumption was primarily responsible for the upward trend in energy turnover at rest during the day. A small ''diurnal'' elevation in oxygen consumption occurred during fasting, with or without exercise. Climate per se did not appear to influence the pattern of resting metabolism. DIETARY DEFICIENCIES Dietary deficiencies produce various symptoms; however, evidence of gross nutrient deficiency is usually delayed for a considerable period of time unless the deficiency is water, carbohydrate, or total kcal. Johnson summarized the more prominent effects of gross nutrient deficiencies, and his listing was modified by Young (1977) and then adapted here (see Table 6-13). Water deficiency has an almost immediate effect, whereas kcal and carbohydrate deficiency effects are seen in a matter of days. Protein and fat deficiencies produce symptoms within weeks and months, respectively. Based on this early information, attention was paid to water, kcal, and carbohydrate deficiencies in a variety of early studies involving hard work by soldiers in either temperate or warm/hot environments (Grande et al., 1957; Taylor and Keys, 1958). The combination of hypohydration and undernutrition was shown to be particularly compromising with respect to physical performance. Significant nitrogen loss in urine and sweat associated with weight loss and, presumably, skeletal muscle hypotrophy was observed. The nitrogen losses found by Grande et al. (1957) are reported in Table 6-14. Should such nitrogen loss continue, troops would be physically com-

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations TABLE 6-13 Rate of Onset of Deficiency Syndromes in Working Men Exposed to Complete Deficiency of One or More of the Important Nutrients Nutrient Times Before Earliest Effects on Performance Appear in Complete Deficiency Deficiency Syndrome and End Result Water A few hours Easy fatigue, poor performance, eventual exhaustion of dehydration Kcal 2 or 3 days Easy fatigue, poor performance Carbohydrate Several days Easy fatigue; poor performance; eventually, nutritional acidosis Protein Probably several weeks Late result, nutritional edema Fats Many months Earliest effects not known   SOURCES: Adapted from Johnson (1943) and Young (1977). promised. Unpublished investigations from the University of Minnesota in the 1950s revealed that a loss of 125 g nitrogen was associated with measurable physiological deterioration, including a significant reduction in walking endurance and aerobic power. A review of the effects of prolonged semi-starvation has been set forth in a classic study by Keys et al. (1950). A further discussion of negative nitrogen balance based on the experience of those working at the University of Minnesota was prepared by Taylor and Keys (1958). Undernutrition is always a problem in military operations for various reasons, among them psychological stress, supply problems, food prepara TABLE 6-14 Cumulative Nitrogen Excretion (Urine and Sweat) During 16 Days on a 1000-kcal Carbohydrate Diet     Control Mean Weight (kg) Nitrogen Excreted, g (± SD) N Water Allowance   Urine Sweat Urine + Sweat 6 900 ml per day 75.4 136.72 ± 10.13 5.02 ± 0.39 141.74 ± 20.44 6 1800 ml per day 73.0 109.94 ± 21.18 5.09 ± 0.48 115.03 ± 21.45 13 Ad libitum 69.1 83.79 ± 14.14 5.41 ± 1.39 89.20 ± 14.74   SOURCE: Adapted from Grande et al. (1957).

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations tion problems, and coping with threats and emergencies. A group led by Sargent and Johnson at the University of Illinois spent considerable time and effort in the 1940s and 1950s working on undernutrition (as well as more normal nutrition). They established fundamental physiological, nutritional bases for an all-environment survival ration (Sargent and Johnson, 1957): Maximal feasible kcal content provided by a balanced mixture of first-class protein, carbohydrate, and fat. The goal should be 2,000 kcal per man per day, of which protein should provide 15 percent of kcal, carbohydrate 52 percent of kcal, and fat 33 percent of kcal. Water allowance as liberal as possible, with a goal of three quarts per man per day for hot weather, and no less than one quart per man per day under any circumstances. An optimal osmotic intake, neither too large nor too small. The goal should be 700 milliosmols per day, provided by the sum of protein and minerals. Within limits set by the recommended proportions of protein, carbohydrate, and fat, minimal ketogenicity, minimal specific dynamic action, and maximal water of oxidation. Although the focus was on adequate carbohydrate supply during the 1940s and 1950s, largely to avoid the debilitating effects of ketosis, there was also concern about adequate protein and preservation of body tissue including skeletal muscle mass. Mitchell and Edman (1949, 1951) said about protein: Considering all evidence, it may be concluded that protein requirements may be slightly increased in the tropics by some 5 to 10 grams daily ... Laboratory experiments show that protein requirements may be increased slightly by (a) a stimulation of tissue catabolism if pyrexia occurs, and (b) by sweat losses of nitrogen uncompensated by diminished losses in the urine. Consolazio and Shapiro (1964) found in the summary of their studies of men exercising under different climatic conditions that protein intake in the hot climate exceeded the National Research Council's recommended allowance of 100 g per day. In contrast to the conclusion of Mitchell and Edman (1949, 1951), Consolazio and Shapiro felt that increased protein intake in the heat was due not to an innate desire for protein, but to the relatively greater caloric intake. Recently, Paul (1989) suggested that because protein and amino acids contribute from 5 to 15 percent of energy for prolonged exercise—with the higher values perhaps associated with glycogen depletion—adequate protein intake is important when exercising in the heat. He pointed out that urine and sweat urea increase during prolonged, relatively intense exercise. Nevertheless, there appears to be no evidence that protein

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations intakes in excess of from 1 to 1.5 g per kg body weight offer any advantage to the mature military person. One possible disadvantage of high protein intakes is the obligatory urine volume required to excrete protein breakdown products, including urea. A PERSPECTIVE The comment of D. B. Dill (1985), a former colleague who was well versed in the desert environment, provides a fitting reminder to the readers of this brief historical review. In the hot desert even a well trained human can sprint only about half the distance one would guess before collapsing. One should respect the incredible intensity of the desert, protect oneself with shade, spare water, slow movement, equally-minded partners, then enjoy and relish its beauty. Unfortunately, military personnel engaged in combat or under the threat of combat may not have the luxury of contemplating beauty, but they nevertheless must deal with the "incredible intensity of the desert." 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.F., and associates 1947 Physiology of Man in the Desert. New York: Interscience Publishers. Buskirk, E.R., and D.E. Bass 1957 Climate and Exercise. Technical Report EP-61, U.S. Army Quartermaster Research and Development Center, Natick, Mass. Buskirk, E.R., M. Kreider, R. Brebbia, N. Morana, F. Daniels, B.E. Welch, J.B. Mann, W. Insull, Jr., and T.E. Friedemann 1956 Caloric Intake and Energy Expenditure in a Sub-Arctic Environment. Report No. EP-33, U.S. Army Quartermaster Research and Development Center, Natick, Mass. Buskirk, E.R., P.F. Iampietro, and B.E. Welch 1957 Variations in resting metabolism with changes in food, exercise and climate. Metabolism 6:144–153. Consolazio, C.F., and R. Shapiro 1964 Energy requirements of men in extreme heat. Pp. 121–124 in Environmental Physi-

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations ology and Psychology in Arid Conditions: Proceedings of the Lucknow Symposium. Liège, Belgium: United Nations: UNESCO. Consolazio, C.F., R. Shapiro, J.E. Masterson, and P.S.L. McKinzie 1961 Energy requirements of men in extreme heat. J. Nutr. 73:126–134. Consolazio, C.F., L.O. Matoush, R.A. Nelson, J.A. Torres, and C.J. Isaac 1963 Environmental temperature and energy expenditures. J. Appl. Physiol. 18:65–68. Consolazio, C.F., H.L. Johnson, and H.J. Krzywicki 1970 Energy metabolism during exposure to extreme environments. Unnumbered report. U.S. Army Medical Research and Nutrition Laboratory, Fitzsimmons General Hospital. Denver, Colo. Dill, D.B. 1938 Life, Heat and Altitude. Cambridge, Mass.: Harvard University Press. 1985 The Hot Life of Man and Beast. Springfield, Ill.: Charles C. Thomas. Dill, D.B., H.T. Edwards, P.S. Bauer, and E.J. Levenson 1931 Physical performance in relation to external temperature. Arbeitsphysiologie 4:508–518. Dimri, G.P., M.S. Malhotra, J. Sen Gupta, T.S. Kumar, and B.S. Aora 1980 Alterations in aerobic-anerobic proportions of metabolism during work in the heat. Eur. J. Appl. Physiol. 45:43–50. Eichna, L.W., C.R. Park, N. Nelson, S.M. Horvath, and E.D. Palms 1950 Thermal regulation during acclimation in a hot dry desert type environment. Am. J. Physiol. 163:585–597. Food and Agricultural Organization of the United Nations 1950 Caloric Requirements. Report of the Committee on Calorie Requirements. Washington, D.C.: United Nations. Galvao, E.G. 1950 Human heat production in relation to body weight and body surface. J. Appl. Physiol. 3:21. Grande, F., J.T. Anderson, and H.L. Taylor 1957 Effect of restricted water intake on urine nitrogen output in man on a low calorie diet devoid of protein. J. Appl. Physiol. 10:430–435. Howe, P.E., and G.H. Berryman 1945 Average food consumption in the training camps of the United States Army (1941–1943). Am. J. Physiol. 144:558–594. Iampietro, P.F., J.A. Vaughn, A. MacLead, B.E. Welch, J.G. Marcinek, J.B. Mann, M.P. Grotheer, and T.E. Friedemann 1956 Caloric intake and energy expenditure of eleven men in a desert environment. Report No. EP-40. U.S. Army Quartermaster Research and Development Center, Natick, Mass. Johnson, R.E. 1943 Nutritional standards for men in tropical climates. Gastroenterology 1:832–840. 1946 Applied physiology. Ann. Rev. Physiol. 8:535–558. Johnson, R.E., and R.M. Kark 1946 Feeding Problems in Man as Related to Environment. An Analysis of United States and Canadian Army Ration Trials and Surveys. Chicago, Ill.: Quartermaster Food and Container Institute for the Armed Forces. 1947 Environment and food intake in man. Science. 105:378–379. Kark, R.M. 1954 Studies on troops in the field. Pp. 193–195 in Nutrition Under Climatic Stress, H. Spector and M.S. Peterson, eds. Washington, D.C.: National Academy of Sciences.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations Kark, R.M., H.F. Aiton, E.D. Pease, W.B. Bean, C.R. Henderson, R.E. Johnson, and L.M. Richardson 1947 Tropical deterioration and nutrition. Clinical and biochemical observations on troops. Medicine 26:1–40. Keys, A., J. Brozek, A. Henschel, O. Mickelsen, and H. Taylor 1950 The Biology of Human Starvation, vols. 1–2. Minneapolis, Minn.: University of Minnesota Press. Klausen, K., D.B. Dill, E.E. Phillips, and D. McGregor 1967 Metabolic reactions to work in the desert. J. Appl. Physiol. 22:292–296. MacGregor, R.G.S., and G.L. Loh 1941 The influence of a tropical environment upon the basal metabolism, pulse rate and blood pressure in Europeans. J. Physiol. (London) 99:496–509. Mason, E.D. 1934 The basal metabolism of European women in South India and the effect of change in climate on European and South Indian women. J. Nutr. 8:695. Mitchell, H.H., and M. Edman 1949 Nutrition and Resistance to Climatic Stress, with Reference to Man. Chicago, Ill: Quartermaster Food and Container Institute for the Armed Forces. 1951 Nutrition and Resistance to Climatic Stress with Particular Reference to Man. Springfield, Ill.: Charles C. Thomas. Paul, G.L. 1989 Dietary protein requirements of physically active individuals. Sports Med. 8:154–176. Robinson, S., E.S. Turrell, H.S. Belding, and S.M. Horvath 1945 Rapid acclimatization to work in hot climates. Am. J. Physiol. 140:168–176. Rose, M.S., and D.E. Carlson 1986 Effects of A-ration meals on body weight during sustained field operations. Report No. T2-87. Natick, Mass.: U.S. Army Research Institute of Environmental Medicine. Rowell, L.B., G.L. Brengelman, J.A. Murray, K.K. Kraning, and F. Kusumi 1969 Human metabolic responses to hyperthermia during mild to maximal exercise. J. Appl. Physiol. 26:395–402. Sargent, F., and R.E. Johnson 1957 The Physiological Basis for Various Constituents in Survival Rations. Part 4. An Integrative Study of the All-Purpose Survival Ration for Temperate, Cold and Hot Weather . Wright Air Development Center Technical Report 53–484. Wright-Patterson Air Force Base, Ohio: Wright Air Development Center. Sawka, M.N., K.B. Pandolf, B.A. Avellini, and Y. Shapiro 1983 Does heat acclimation lower the rate of metabolism elicited by muscular exercise. Aviat. Space Environ. Med. 54:27–31. Sen Gupta, J., P. Dimri, and M.S. Malhotra 1977 Metabolic responses of Indians during submaximal and maximal work in dry and humid heat. Ergonomics 20:33–40. Shvartz, E., Y. Shapiro, A. Magazanik, A. Meroz, H. Bernfeld, A. Mechtinger, and S. Shibolet 1977 Heat acclimation, physical fitness, and responses to exercise in temperate and hot environments. J. Appl. Physiol. 43:678–683. Swift, R.W., and C.E. French 1954 Energy Metabolism and Nutrition. New Brunswick, N.J.: Scarecrow Press. Taylor, H.L., and A. Keys 1958 Criteria for fitness and comments on negative nitrogen balance. Ann. N.Y. Acad. Sci. 73:465–475.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations Welch, B.E., L.M. Levy, C.F. Consolazio, E.R. Buskirk, and T.E. Dee 1957a Caloric intake for prolonged hard work in the cold. Report No. 202. U.S. Army Medical Nutrition Laboratory, Denver, Colo. Welch, B.E., J.G. Marcinek, E.R. Buskirk, and P.F. Iampietro 1957b Caloric intake and energy expenditure of eight men in a temperate environment. Report No.196. U.S. Army Medical Nutrition Laboratory, Denver, Colo. Welch, B.E., E.R. Buskirk, and P.F. Iampietro 1958 Relation of climate and temperature to food and water intake in man. Metabolism 7:141–148. Young, D.R. 1977 Physical Performance Fitness and Diet. Springfield, Ill.: Charles C. Thomas. Young, J.J., M.N. Sawka, L. Levine, B.S. Cadarette, and K.B. Pandolf 1985 Skeletal muscle metabolism during exercise is influenced by heat acclimation. J. Appl. Physiol. 59:1929–1935.