The physiological psychology of hunger: a physiological perspective.

Hunger and satiety are usually discussed from the perspective of the central nervous system. In this paper we instead find the foundation for an understanding of hunger in the basic biochemical and physiological processes of energy metabolism. Such considerations suggest that the stimulus for hunger should be sought among changes that occur in the supply of metabolic fuels rather than in the utilization of specific nutrients or in the levels of fuel reserves. This line of reasoning diverts attention from the brain, which is not usually subject to dramatic fluctuations in its fuel supply, and focuses instead on the intestines, adipose tissue, and liver, the three peripheral organs that are most involved in the production or delivery of metabolic fuels. We propose that the stimulus for hunger derives from information provided to the brain by the liver in the course of normal hepatic function. More specifically, the stimulus for hunger may be associated with an alteration in oxidative metabolism within the liver, with food intake reversing that change. This view of hunger conforms closely to the fundamental features of caloric homeostasis and makes unnecessary such traditional hypothetical constructs as hunger and satiety centers, glucostat, lipostat, and body weight set point.