Regulation of hunger and satiety in man.

From the perspective presented in this minireview, it is clear that a variety of psychological and physiological factors interact to regulate feeding behavior. The hunger-satiety cycle involves preabsorptive and postabsorptive humoral and neuronal mechanisms. Psychological, social and environmental factors, nutrients and metabolical processes and gastric contractions originate hunger signals. Eating, in turn, activates inhibitory signals to produce satiety. Because of the delay between the swallowing of food and the digestion of food, the satiety mechanism requires a short-term signal to prevent over-eating. This short-term satiety signal is activated by psychological factors (such as sensory-specific satiety), chemical senses (taste and smell) and mechanical factors related to the process of swallowing and gastric distension. The long-term satiety is then activated by the chemoreception of nutrients and peptides by the gastrointestinal system (including the liver), the CNS and by intrinsic CNS mechanisms. The fine regulation of feeding behavior through these mechanisms will ensure the maintenance of normal energy metabolism. It is important to note, however, that despite all the efforts that have gone into the study of peripheral and central mechanisms of ingestive behavior--expressed in thousands of publications related to the anatomy, chemistry and metabolism, physiology and behavioral aspects of feeding--we will lack an understanding of the interactions among signals within a system or among different systems.