This article examines how the depletion and replenishment of various energy stores give rise to periodic eating and how constant body-energy levels are maintained over time.

Measures of the energy expended throughout the 24-hour feeding pattern in rats indicate that two different energy stores (one of small capacity and one of large) determine two superimposed feeding periodicities: one from meal to meal (prandial), the other from day to night (nycthemeral). The article reviews how experimental overrepletion or overdepletion of gastrointestinal content, blood glucose, or body fats affect food intake. These data suggest that gastrointestinal content determines both meal size and meal-to-meal periodicity. Other evidence indicates that glucose uptake rate in tissues, which is modulated by fat synthesis and fat mobilization, affects the periodic onset of feeding and the difference between nocturnal and diurnal postprandial satiety.

There follows an examination of the neuroendocrine bases for the interacting mechanisms governing energy input and output balance and of the role of the ventromedial hypothalamus in body-fat regulation and the lateral hypothalamus in feeding.