Appetite

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.

Cannon and Washburn (1912) proposed that eating begins when we have an empty stomach. They suggested that the walls of an empty stomach rub against each other to produce what are commonly called "hunger pangs". Some skeptics called Cannon's explanation of hunger "the rumble theory". However, observations of surgical patients indicated that there was more to the onset of eating than hunger pangs. Removal of the stomach did not abolish hunger pangs, and these patients reported the same feelings of hunger and satiety that they had experienced before surgery (Inglefinger, 1944). (The patients' stomachs had been removed because of cancer or large ulcers, and their esophagi had been attached directly to their small intestines). Although the patients ate small frequent meals because they had no stomachs to hold food, their reports of feelings of hunger and their total food intake were essentially normal.

Depletion of the body's store of nutrients is a more likely cause of hunger. The primary fuels for the cells of our body are glucose (a simple sugar) and fatty acids (compounds produced by the breakdown of fats). If the digestive system contains food, these nutrients are absorbed in the blood and nourish our cells. But the digestive tract is sometimes empty; in fact, it is empty when we wake up every morning. There must be a reservoir that stores nutrients to keep the cells of the body nourished when the gut is empty. Indeed, there are two reservoirs: a short-term reservoir and a long-term reservoir. The short-term reservoir stores carbohydrates, and the long-term reservoir stores fat.

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