satiety and cold induces hunger—adds to the confusion in this area. In general, more attention should be paid to whether the effect of heat on appetite suppression is expressed in terms of smaller meals (presumptive satiety effects) or less frequent meals (presumptive hunger effects); of course, these alternatives are not perfectly independent of one another. The frustratingly speculative nature of the foregoing discussion, in fact, is a reflection of the fact that "in most cases the measurement of postprandial heat [has been] undertaken with a totally different objective than that of assessing its effects on food intake" (Rampone and Reynolds, 1991). Thus, the call for more research may be extended to all aspects of endogenous heat production as a moderator of appetite.
Lack of adequate food induces cold. Keys et al. (1950) found that their semistarved volunteers complained of the cold even in warm summer weather. One might be tempted to suggest underfeeding troops in hot climates in order to minimize their problems with heat. Although a somewhat reduced intake is probably desirable and inevitable, given the various regulatory pressures that are activated automatically, deliberate food restriction below what the troops naturally desire would probably not be desirable, owing to all the negative effects of maintaining a suboptimal body weight. Metabolism is, if anything, speeded up in the heat and intake is reduced; the net effect is likely to be significant weight loss, and if that weight loss occurs in the absence of a resetting of the BW set-point, the result is likely to be a substantial energy deficit.
Most humans are not built to operate optimally in extremes of temperature. If faced with severe heat, people may reduce their intake and rely on metabolic processes to dissipate as much heat as possible, but this ultimately represents a loss of energy that might well interfere with other demands placed on them (for example, demands for intense activity). The solution, it would seem, is to avoid severe heat and function in a climate where thermoregulation is not a difficult challenge. Hot environments by definition provide such a challenge, but the best solution may be to find ways to keep cool, or at least thermoneutral, other than—or in addition to—reducing intake.
The ability to dissipate heat depends on various factors, not the least of which is physique. Bergmann's rule states that 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 (Beller, 1977). Allen's corollary to Bergmann's rule gives a heat-