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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 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.


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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