Hunger regulation. Hunger is now known to be regulated on a short‐term basis by two clusters of cells (called nuclei) in the hypothalamus of the brain, the ventromedial hypothalamic (VMH) and the lateral hypothalamic (LH) nuclei (Figure 1).
The Hypothalamic Nuclei
Lesioning (destruction) produces effects on motivated behavior that are opposite those produced by electrical stimulation of the same nucleus. Damage to a rat's LH causes the rat to stop eating (become aphagic) and eventually starve to death even with an abundance of food. Electrical stimulation of the LH, however, causes it to eat. Conversely, damage to a rat's VMH causes it to overeat (become hyperphagic). (If an adult female rat of a species weighs 350 grams, a hyperphagic rat of the same species can weigh over 1,000 grams.) Electrical stimulation in the same VMH nucleus produces cessation of eating.
Long‐term regulation of hunger is less understood, but one theory, the set‐point theory, suggests that the body has a weight regulatory system, which establishes a “set‐point” that regulates body weight on a long‐term basis. This theory could explain, for example, why a hyperphagic rat, even though very overweight, finally stops eating. While the set‐point mechanism is not known, one view is that the regulation includes an interaction with the level of body fat. If body fat increases, eating is less frequent and activity increases; the converse is true if body fat decreases.
Other changes can also affect hunger, such as changes in glucose (blood sugar) and hormone levels. For example, the hormone insulin diminishes the blood glucose level, producing hunger and thus increasing eating behavior. In addition, external cues may affect eating behavior, for example, the sight or aroma of food or the sight of other people eating.
Eating disorders. Theoretical explanations of eating behavior are still being explored, particularly with the increasing occurrence of eating disorders such as anorexia nervosa and bulimia nervosa. (The majority of individuals with eating disorders are female, a phenomenon possibly explained by society's expectations that the ideal female must be very thin.)
In anorexia nervosa, the individual suffers starvation caused by repeated calorie restriction. Ultimately, the disorder can be fatal (as it was for singer Karen Carpenter). A person afflicted with bulimia nervosa goes on eating binges and then purges, inducing vomiting or using laxatives, to get rid of the ingested food. This behavior also is ultimately detrimental to health. Obesity, another failure of hunger regulation, is found in individuals of all ages and genders.