Appetite is the desire to
eat food, sometimes due to
hunger. Appealing foods can stimulate appetite even when hunger is absent. Appetite exists in all higher life-forms, and serves to regulate adequate energy intake to maintain
metabolic needs. It is regulated by a close interplay between the
digestive tract,
adipose tissue and the
brain. Appetite has a relationship with every individual's behavior. Appetitive and consummatory behaviours are the only processes that involve energy intake, whereas all other behaviours affect the release of energy. When stressed, appetite levels may increase and result in an increase of food intake. Decreased desire to eat is termed
anorexia, while
polyphagia (or "hyperphagia") is increased eating. Dysregulation of appetite contributes to
anorexia nervosa,
bulimia nervosa,
cachexia,
overeating, and
binge eating disorder.