A Mechanism of Regulation of Food Intake *

Regulation of food intake is a term which includes all of the reactions through which an animal (i) maintains a constant intake while environmental and metabolic conditions are constant, and (ii) adjusts its intake whenever environmental or metabolic conditions are altered. What an animal eats and how much are usually thought to be determined by the energy requirements of the body; but every careful observer who has conducted feeding experiments knows that there are many circumstances in which the amount of food eaten is not related to energy expenditure. For example, most mammals will not eat when they are deprived of water, because the demand for energy is secondary to preventing dehydration. They also fail to eat when placed in a hot environment with free access to water and food. There is, therefore, no simple correlation between energy needs and food intake which is valid under all conditions, and it is our purpose now to present the hypothesis that the important factor in regulation of food intake is not its energy value, but rather the amount of extra heat released in its assimilation. Our data do not exclude the possibility that there are other bases for this regulation; as there are several factors in regulation of respiration (CO2 tension, pH, 02 tension, etc.), so there may be more than one factor in regulation of feeding. Yet the intake of energy as food seems to a large extent to be regulated indirectly via the heat liberated in assimilating food, much as oxygen intake is regulated via carbon dioxide concentration and pH of the blood. Other theories of hunger, appetite, and satiety, based on Cannon's9 and Carlson's'0 studies of sensation from the stomach, do not account in a quantitative way for regulation feeding, nor explain the observation that animals eat different amounts of different diets. The ability of animals to change their intake when the composition of food is altered suggests that animals recognize some quality in food, and that this quality may be correlated with regulation of the amount of food eaten. This quality we have arbitrarily called the intrinsic food factor, and we have concluded that it may be identical with the specific dynamic action, since it cannot be any one of the more obvious dietary constituents, including the caloric value of the food. Following feeding, the heat production is greater than before the food