Hunger regulation. Hunger is known to be regulated in the short term by two groups of cells (called nuclei) in the hypothalamus of the brain, the ventromedial hypothalamic (VMH) and lateral hypothalamic (LH) nuclei.
The injury (destruction) produces effects on motivated behavior opposite to those produced by the electrical stimulation of the nucleus itself. Damage to a rat’s LH causes the rat to stop eating (become aphasic) and eventually starve even with plenty of food.
However, the electrical stimulation of LH makes you eat. Conversely, damage to a rat’s VMH causes it to overeat (become hyperphagic). (If an adult female rat of one species weighs 350 grams, a hyperphagic rat of the same species can weigh more than 1000 grams.) Electrical stimulation in the VMH nucleus itself causes the power to fail.
Long-term regulation of hunger is less well known, but one theory, the set point theory, suggests that the body has a weight regulation system, which establishes a “set point” that regulates body weight in the long term.
This theory could explain hunger motivation, for example, why a hyperphagic rat, despite being very overweight, finally stops eating. Although the mechanism of the setpoint is not known, one view is that regulation involves an interaction with the level of body fat. If you increase your body fat, you eat less frequently and increase activity; the opposite is true if body fat decreases.
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Other changes can also affect hunger, such as changes in glucose (blood sugar) and hormone levels. For example, the hormone insulin lowers the level of glucose in the blood, causing hunger and thus increasing eating behavior. Additionally, external cues can affect eating behavior, such as the sight or aroma of food or the sight of other people eating.
Food problems in hunger motivation. Theoretical explanations of eating behavior are still being studied, particularly with the increasing emergence of eating disorders such as anorexia nervosa and bulimia nervosa. (Most people with eating disorders are women, a phenomenon perhaps explained by societal expectations that the ideal woman should be very thin.)
In anorexia nervosa, the individual suffers from hunger caused by repeated calorie restrictions. Eventually, the disorder can be fatal (as it was for singer Karen Carpenter). A person with bulimia nervosa continues to overeat and then purges, causing vomiting or using laxatives, to eliminate ingested food. This behavior is also ultimately harmful to health. Obesity, another flaw in hunger regulation, is found in people of all ages and genders.