act as a brake on the feeding centers and make people want to stop eating. The feeding and satiety centers are extremely complicated mechanisms. They may be disturbed by such causes as emotional pressures and physical characteristics. For example, emotional pressures such as great disappointment cause some people to stop all physical activity. At such times, these people eat more than they usually do--and gain weight. Other people move around more and eat much less--and lose weight. Some scientists believe that overfeeding infants causes them to develop too many fat cells. They claim that these cells store fat so readily that such people are likely to be obese for the rest of their lives. Physical Inactivity is a leading cause of obesity among all age groups, but especially among children and teen-agers. Most obese young people do not eat more than young people of normal weight. But they are so inactive that, even with a moderate appetite, they eat more than they need--and accumulate excess fat. Exercise uses up many calories, and the more vigorous the activity, the more calories are used. A 150-pound (68-kilogram) person walking at an average speed of 3 1/2 miles (5.6 kilometers) per hour will use up 502 calories--the number of calories in a malted milk shake--in 97 minutes. That person will use up the same number of calories in 61 minutes by riding a bicycle, or in 26 minutes by running. The number of calories used is proportional to a person's weight. If you weigh 75 pounds, for example, you will use up half as many calories as a 150-pound person by doing the same exercise for the same length of time. The appetite of active people can increase if they become very active. If they become inactive, their appetite will not necessarily decrease. Appetite does not go below a minimum level even if activity drops. Heredity. Scientists have learned much about the relationship between heredity and obesity in animals, especi...
