In HER 39 years, Claudia Hallblom has, by her own estimation, lost and regained about 1,000 pounds.
Her success at losing weight was always driven by a goal, such as looking nice for her graduation or wedding. Her tactics usually included strict calorie-counting. But success on the scales was always fleeting. Sooner or later, she would revert to her old habits and no longer feel motivated to change.
"I didn't know how to lose weight and keep it off," the Downey woman says.
Most people can lose weight. But few can maintain their new weight for long. Researchers are now tackling that problem, and what they're learning is disconcerting. The human body, it seems, is designed to sabotage weight loss at every turn -- once a body has been fatter, it wants to get back to the weight that it used to be. Physiology is cruelly changed in two ways: The body needs fewer calories to maintain itself, but its craving for food is more intense.
Becoming overweight, in other words, is like being issued a credit card with an uncomfortably high balance that you'll probably end up paying off forever. Making sure the pounds stay off means pitting one's willpower against a swarm of biological processes involving the brain, hormones, metabolism and fat storage.
"There is a big shift toward understanding long-term weight maintenance," says Paul MacLean, associate professor of medicine at the University of Colorado, Denver. "We have a huge number of diet books and diet programs, and if you do them, you can lose weight. The big problem is keeping it off. The recent estimates are that 5% to 10% of people are successful at keeping weight off on a long-term basis."
But before you throw up your hands and reach for the Twinkies, consider this: Scientists think the truth will set us free -- that understanding the stubborn biological processes at work will lead to ways to fight back and outsmart them.
Exercise, it's known, buffers the post-diet body against regaining weight, in ways that researchers are just starting to comprehend. Certain foods, scientists believe, may help stave off weight regain too. And medications now in development target some of the biochemistry thought to be linked to packing the pounds back on.
"There are strong physiological adaptations to weight loss that promote weight regain," MacLean says. "The good news is we know a big part of the problem and why we haven't been successful over the past several decades."
The energy gap
Human biology -- for obvious adaptive reasons -- is designed to protect against weight loss and potential starvation. And after a period of obesity, the body may permanently alter the way weight is regulated by more aggressively stimulating appetite and signaling the body to protect fat stores.
Metabolism has changed: the body now needs about eight fewer calories per day for each pound of weight that was lost. That means someone who loses 40 pounds will require about 320 calories fewer each day than they did before the weight loss. This difference in energy needs before and after weight loss has been dubbed the "energy gap" by University of Colorado professor James O. Hill, director of the Center for Human Nutrition in Denver.
Appetite hormones change too. The hormone leptin, for example, is a major appetite regulator -- it tells the body to stop eating and store fat after meals. Some people may be genetically prone to having lower leptin levels, making them more prone to obesity. But studies also show that, after a weight loss, leptin levels are lower than what they used to be. That means appetite is less easily quelled. It's like a car that has suddenly lost its brakes.
Another hormone, ghrelin, stimulates food intake -- levels in the brain fall lower after a meal. However, after a weight loss, ghrelin levels in the blood generally increase, and the fall-off after mealtimes isn't as marked.
"You lose 10% of your body weight. All of a sudden all these systems kick in to try to keep you from losing weight," says Dr. Ken Fujioka, director of nutrition and metabolic research at the Scripps Clinic in San Diego. "People are mad at themselves or depressed after they regain the weight. But I explain: It's not you. Biology has kicked in now. . . . You are hungry all the time. You think about food all the time."
The brain isn't the only thing acting to promote weight regain. MacLean's research suggests that the central nervous system collects and interprets signals from the intestines and peripheral tissues, such as fat stores in the abdomen, to fight weight loss or regain pounds that were lost.