The Theory of Losing Weight

If you are on a diet and reached your goal, chances are good that when you stop dieting you will regain all the weight you lost. After several weeks on a low-calorie diet—900 calories or fewer—the body conserves energy by slowing the speed at which it bums calories. The slow-down explains in part why your weight loss may cease after a few weeks.

When you eventually return to eating a normal amount of food, your body may continue to bum calories at the slower rate, storing the remaining calories as fat. So if you are on a strict diet, your body may need fewer calories to maintain the same weight; losing weight becomes more difficult.

Doctors know that as you gain weight the fat cells in your body (most of us average 30 billion of them) become enlarged. But there is a limit to how big a fat cell can get, and very fat people develop additional fat cells-sometimes more than 100 billion. It now appears that you can add fat cells at any point during your life, although the number you have is influenced by a combination of history of dieting and your genetic make-up.

Fat cells are different from other cells. They are made mostly of fat instead of protein, and apparently they never go away, even after dieting. Instead, they merely shrink. Dr. Junes Hirsch of Rockefeller University has examined the body tissue of very fat people who have lost weight, and found that it resembles that of starvation victims. Perhaps, he supposes, it is the billions of undersize, "hungry" cells that drive many formerly fat people off their diets.

New research suggests that your hungry cells aren't the only signal senders that attempt you toward the refrigerator. Another criminal may be the hormone insulin. Insulin turns sugar and fat into fuel for the body. In addition, some researchers believe that high levels of insulin are a factor in hunger and appetite—and may drive you to overeat.

Exercise helps maintain your weight and seems to bring insulin levels down, says Dr. Donald S. Robertson, a medical director. "Any weight-loss program must fail," he says, "unless it incorporates a certain amount of exercise."