The gastrointestinal tract makes a signiยฎcant contribution to the essential processes whereby energy and micronutrients are made available in a controlled fashion to the body. The taste and smell of food and gastric emptiness can provoke ingestion, while gastric distension and absorption of nutrients may signal cessation of ingestion. The former processes are often called hunger' and the latter satiety'.
Tasting food appears to contribute to satiety by modulating the proportions of different nutrients that are ingested. Speciยฎc mechanisms appear to exist which control separately the intake of foods with widely differing tastes (Hetherington et al., 1989). Food entering the stomach and causing gastric distention is a powerful satiety signal. Patients who vomit after eating as a result of bulimia nervosa sometimes enter a cycle of repeated overeating and vomiting which suggests a failure of satiety due to repeated emptying of the stomach. Rats in which the stomach is drained during feeding show severely impaired satiety suggesting that the passage of food through the oral cavity cannot, alone, inhibit food intake (Antin et al., 1975).
Certain putative satiety signals such as cholecystokinin (CCK) are thought to exert their action, at least partially, through the inhibition of gastric emptying and the resulting gastric distension that is provoked (Moran and McHugh, 1982). The inhibitory effect of CCK on feeding is observed at birth in rats when gastric, but not brain, CCK receptor systems have developed (Robinson and McHugh, 1995). CCK has been found to be reduced in bulimia nervosa (Geracioti and Liddle, 1988;Devlin et al., 1997) and increased (Alderdice et al., 1985) or normal (Abell et al., 1987) in anorexia nervosa. It may therefore contribute respectively to under-and over-eating in these conditions.
The small intestine has an important role in controlling food intake. Nutrients reaching the ileum have a powerful inhibitory effect on eating European Eating Disorders Review