America's Obesity Crisis:Eating Behavior: Why We Eat

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Although anorexia and obesity look nothing alike in clinical terms, there are similarities. People with both disorders tend to organize their days around eating and allow food to loom too large in their lives. "People who are anorexic and people who are overweight often begin to get phobic about food," says Dr. William Davis, of the Renfrew Center in Philadelphia, which treats patients with eating disorders. Food for them is much more than a source of nourishment; it can become a substitute for self-esteem and a vehicle for exercising--or losing--control over the body.

But scientists who have studied both groups say that underneath these similarities are two very different syndromes. "Obesity is at its base a metabolic disorder," says Dr. Lee Kaplan, director of the Obesity Research Center at Massachusetts General Hospital. Anorexia and bulimia, he maintains, "are primary psychiatric disorders."

The human body is designed to eat, and eating stops under normal circumstances only when the body senses it has enough energy for its immediate needs and enough stored away for future tasks. "It's hard to lose weight because the body wants to gain it back," says Kaplan. "In a competition between willpower and the body, the body always wins."

Except when an eating disorder has hijacked the process. Anorexics and bulimics are more successful at losing weight than people on diets because they have managed to throw this basic drive to eat into reverse. Through sheer force of will, anorexics convince their body that it doesn't need food. "Anorexics are able to do things that are clearly beyond what a normal person is capable of doing," says Kaplan. "Theirs is extreme behavior often driven by an inappropriate and distorted body image."

By contrast, people who gain weight are following the body's natural urge to hoard calories. Slight changes in the way you burn and store calories can lead, over time, to piling on the pounds. And while some of the factors responsible for these changes are within your control--how much you exercise or whether you take a second helping of ice cream--most are either inherited or the inbred responses of an organism that is designed to protect itself from starvation. Stress, sleep deprivation and long days packed with constant activity have a tendency to accumulate weight. "If we took away cars and television and computers, and stopped eating fast food, but were still exposed to the other stresses of modern life, I don't think we would eliminate obesity," says Kaplan. "We might dampen it, but we wouldn't eliminate it altogether."

And that's why treatments for obesity differ so much from those for anorexics. People who starve themselves tend to respond better to therapies and behavior-modification approaches that address their distorted body image and underlying emotional issues. People with overeating problems are often successfully treated with a more physiological approach, usually through diet and exercise and, sometimes, medications that curb appetite or burn calories more efficiently.