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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations
exposed to the cold is faster gastric emptying (Logue, 1986). Logue notes that rats exposed to the cold initiate more meals but do not eat more at a given meal. Presumably, gastric emptying rate does not affect the initial repletion rate of the stomach, and consequently the size of the meal, but does affect the length of time until the stomach again "demands" repletion, and consequently the frequency of meals. The faster the stomach empties, the sooner the next meal must begin. To extrapolate to the presumably reduced gastric emptying rate in animals exposed to the heat, one might speculate that the slowing of the digestive process is a means of muting the thermic effect of food.
Casual inquiry yields a broad consensus that BW declines in the summer and rises in the winter. This seasonal variation is sometimes thought to be accompanied by a corresponding variation in appetite, although interestingly, people appear to be less cognizant of how much they eat than of how much they weigh. The thermoregulatory viewpoint considered above would seem to predict a decline in appetite in the summer heat as a means of ensuring that endogenous heat does not threaten one's thermoregulatory capacity. What remains uncertain—even if the appetitive shift occurs—is whether the shift in body weight is regulated or not. That is, does BW set-point shift downward in the hot months, dragging appetite with it? Or does appetite decline on its own, as a thermoregulatory tactic, while BW set-point remains high?
The need for less internal heat in the summer seems to be an adequate physiological rationale for lowered summer appetite. Other reasons may be suggested, however—notably, that people wear less clothing in the summer for thermoregulatory reasons and therefore become more concerned with their physical appearance. A bathing suit demands a slim physique, and perusal of popular magazines suggests that much of the springtime is devoted to shaping up for summer.
Among those who are exposed to summer heat involuntarily, reduced appetite would be expected. Solid evidence in support of this expectation is not abundant, if only because it has not been systematically collected. We know that the farmed polecat reduces its intake and weight during the summer months (Korhonen and Harri, 1986).
The most salient outcome of this literature search—other than consensual agreement with the general proposition that heat impairs appetite—is the dearth of actual experimental research on human consummatory response to variations in heat. It is somewhat reassuring, then, to note that retailers corroborate the consensual impression, often with hard data (sales