and Cabanac (1989) recently demonstrated that the postprandial thermogenic effect of food intake has both a cephalic and a gastrointestinal phase. The cephalic effect (which was evident in subjects who did not even swallow the food but merely chewed and spit it out) was stronger than the subsequent gastrointestinal effect following consumption. Some researchers (Penicaud et al., 1986) argue that temperature control has primacy over food intake control.
Osmotic factors have also been shown to affect food intake (see discussion in Chapter 15). Ingestion or intubation of hypertonic solutions results in decreased food intake in rats (Ehman et al., 1972; Kozub, 1972). This reduction in intake is a protective mechanism that is demonstrated under conditions of total water deprivation, which drastically reduces eating in most species (Thompson, 1980). It appears that, to a large extent, decreased food intake in unacclimatized subjects in tropical climates may be mediated by hypertonicity associated with initial dehydration and may improve as acclimatization occurs (Bass et al., 1955).
Chapter 10 provides a discussion of the evolutionary aspects of survival in hot environments. For example, a bulkier shape minimizes heat loss, because the bulkier animal has a relatively smaller ratio of skin surface to metabolically active bulk and skin surface determines heat dissipation (Belief, 1977). Physical anthropologists (see Belief, 1977, for a review) have long noted a correspondence between physique and climate. The fact that linear physiques generally do better in the heat may be seen as an evolutionary selection principle. The endomorphy of a population, however, is not correlated with mean annual temperature so much as with mean January temperature (in northern latitudes) (Beller, 1977). It is quite possible that adaptation to one sort of challenge may prove to be contra-adaptive in some other sense. Animals and people who maintain a body weight below the set-point show aberrant eating patterns, hyperemotionality (including irritability), distractibility, and a reduced sex drive (Nisbett, 1972).
Body temperature increases under acute stress, which may elevate the thermoregulatory set-point—or simply add metabolic heat. Normal eaters in both laboratory and field settings respond to stress by decreasing their food intake. Not only does the stress of a hot environment involve the need for