One consensual belief, at least among nonscientists, is that hot foods have a greater thermogenic effect. Accordingly, people seek hot foods when they are cold, and cold foods, if any, when they are hot. Turning this prescription around, the conclusion emerges that hot foods ought to have a greater suppressive effect on appetite than cold foods.
Because warming a food tends to enhance its flavor and aroma (Trant and Pangborn, 1983), one might expect that hotter, more palatable food will generate increased intake initially, with perhaps a subsequent caloric compensation—or perhaps not, depending on the strength of compensatory pressures. Actually, one should be careful about assuming that accentuating the flavor will make the food more palatable; some things—notably beverages such as water—are more palatable when cool (Szlyk et al., 1989). And if the food is unpalatable to begin with, warming it may make it taste worse! Holding intake constant, one might expect hot food to suppress appetite by suppressing gastric emptying rate, just as exposure to cold environments speeds gastric emptying, as shown above. Or hot food might suppress appetite by raising body temperature and inducing satiety.
No significant effect on subsequent intake of cheese sandwiches or on sensations of hunger or fullness was observed when experimental subjects were given a fixed portion of V8 juice served at 1°C or 60° to 62°C (Rolls et al., 1990). The cold juice, while not affecting intake, did reduce reported desire to eat, in male subjects only, and reduced thirst as well. No clear explanation is available for the ambiguously suppressive effect of a cold beverage on mens' appetites.
Notwithstanding these sparse and nondefinitive data, there is a strong consensus among retailers and their customers that cold foods are preferred when the ambient temperature is high (unpublished data from consumer survey, 1991). The summer sales peak for ice cream would seem to depend more on the "ice" than on the "cream." In the words of one restaurateur, ''cold menu items make them [the customers] feel even cooler.'' Soup and bakery item sales are slow in the summer.
The effect of food temperature on eating in humans may be powerful, if as yet undemonstrated; in other species, it appears to be negligible. Rats who were served cold (12°C), normal (29°C), or hot (48°C) pellets showed only a weak and insignificant tendency to eat more of the hotter food. As with humans, one is entitled to wonder whether hotter food might smell or taste better, enhancing appetite, while also providing more energy and suppressing appetite. Intriguing studies in ruminants (Bhattacharya and Warner, 1968; Gengler et al., 1970) indicate that if the rumen is heated by the addition of warm water or by heating coils, intake may decline by as