. "6. Energetics and Climate with Emphasis on Heat: A Historical Perspective." Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press, 1993.
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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 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-