Do It by Exercise

Most fat men do not exercise enough -- sometimes on the theory that exercise will only make them hungrier.

For many, this may be wrong, reports Dr. Jean Mayer in Science. By a quirk of body chemistry, the brain's appetite-regulating centers can create the opposite effect -- if you exercise enough, you may eat less and get thinner.

Dr. Mayer, a top nutritionist at Harvard's School of Public Health, believes that his theory applies widely to U.S. men who now weigh an average seven pounds more than they did 50 years ago, even though they consume less calories -- they have cut down on exercise even more than on food.

The old assumption that there is a straight-line relationship between energy expenditure and appetite is an over simplification, says Dr. Mayer. Appetite is controlled by two parts of the brain's hypothalamus. One is a hunger center, the other a satiety center. When energy output is in the middle range, the centers balance neatly, switching one another on and off. But not so at the ends of the activity scale.

When a man is physically overworked to the limits of endurance, says Mayer, he loses appetite, eats less and loses weight. Reason: the hunger center cannot keep up with the body's energy output. Conversely, if a man sits at a desk all day, he may stay hungry. One possible reason: messages to the satiety center do not get through. This phenomenon has long been exploited by farmers who keep animals cooped up to fatten them.

In a study of Boston schoolgirls, Dr. Mayer found that obese girls ate less than normal-weight girls of the same age and height. But the obese girls expended only one-third as much energy. Mayer agrees that obesity has no single, simple cause; such hereditary factors as metabolism and body build, as well as reaction to stress, are also involved. But there is one universal way to control obesity--exercise.

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