Regulation of Food Intake
Even if it appears otherwise, food intake is generally regulated with great precision. The weight of a nor-mal human is relatively constant over a long period. Studies show that if animals are starved for some time and then permitted to eat as they wish, they only increase their food intake until they regain their lost weight.1Similarly, if an animal is force-fed to make it obese and then is allowed to eat freely, the food in-take is diminished until the excessive weight gained is lost. The area of the brain known as the hypothal-amus is responsible for regulating the appetite.
The hypothalamus has two areas—the feedingcenter and the satiety center. Stimulation of thefeeding center increases food intake, and stimulation of the satiety center reduces food intake. The interac-tion of both centers regulates how much an individ-ual eats. It has been shown that the cells in the sati-ety center become less active if the glucose level in the blood reaching the center is low. This, in turn, makes the feeding center more active and more food is taken in. Some other signaling molecules in the blood that affect the hypothalamus and decrease ap-petite are the hormones glucagon, epinephrine, and leptin (hormone from fat cells). Certain signaling molecules, such as growth hormone, glucocorticoids, insulin, and progesterone, produce an increase in ap-petite. Many of the drugs given in weight reduction programs effect the appetite by affecting the food centers in the hypothalamus.
In addition to the hypothalamus, other areas in the brain determine what is eaten. Researchers have shown that lesions in certain areas of the temporal lobe of the brain can make it difficult for an individ-ual to distinguish between edible and inedible and to have a tendency to orally explore all kinds of objects.
Regulation of food intake is a complex process. Other areas of the body other than the brain also have an effect on food intake. Food in the gut can in-hibit food intake. It is believed that the amount of fat in the body sends feedback to the brain in some man-ner that controls the appetite. It is also well known that contractions of the empty stomach—hunger pangs—stimulate appetite. Another major factor for food intake in humans is the culture, environment, and past experiences relative to the taste, sight, and smell of food. Research is underway to explain the actual cause of eating disorders.