For the first time, scientists may be able to explain dieters' complaints that no matter how hard they try, they can't keep off lost weight.
Researchers at the New York Obesity Research Center at Rockefeller University report today on 10 years of painstaking research that show that the body goes to remarkable lengths to maintain the weight it had at the start of dieting. It does so by slowing metabolism--reducing the number of calories required for breathing, maintaining body temperature, circulating blood and digesting food--while increasing the efficiency of muscles so that fewer calories are burned during exercise.
The results, which appear in the New England Journal of Medicine, were obtained in special hospital laboratories where the researchers could measure every calorie consumed by subjects and every calorie spent. The findings indicate that the individual who loses weight faces a lifelong battle to maintain that loss.
"You can't simply go on a diet and eradicate the (obesity) problem," said Dr. Jules Hirsch of Rockefeller. "People who lose weight are going to continue to have this underlying problem" that will lead to regaining the weight unless they eat less than researchers had previously believed, increase their physical activity, or both.
The study suggests that a dieter who does not exercise will have to consume 15% fewer calories than researchers had previously believed to maintain the reduced weight. Those who do exercise can eat a little more.
"You are going to have to increase activity levels and maintain them," said Dr. Van Hubbard, chief of the nutritional services branch at the National Institute of Diabetes and Digestive and Kidney Disease. "This physical activity doesn't have to be performed in health clubs or in aerobic exercise, however. It can just be more walking, more taking of stairs, more moving around in general."
The new results and other studies also should help to change the attitude of physicians, employers and others who castigate obese people for overeating and lack of willpower, Dr. William I. Bennett of Cambridge Hospital wrote in an accompanying editorial. Dieters, he said, "will not be helped by relentless moralizing and easy solutions reflecting a theory of gluttony that does not stand up to the available evidence."
Obesity is a major health problem in the United States that continues to increase. Today, one in every three people in the country is overweight, compared to one in four in 1980.
Obesity has a substantial impact on public health, markedly increasing the incidence and severity of diabetes, hypertension, heart disease, cancer, arthritis and other disorders. The United States spends more than $400 billion annually in health costs directly related to obesity, according to the C. Everett Koop Foundation, a public health organization founded by the former surgeon general.
In attempts to lose weight, Americans spend as much as $50 billion every year, most of it wasted, according to experts. "Tens of millions of people are dieting at any one time, spending billions on weight loss programs, yet few reduce their body fat to a healthy level and even fewer maintain the weight loss beyond two or three years," said Dr. Judith S. Stern of UC Davis, who chaired a 1994 National Academy of Science panel evaluating weight loss programs.
The 18 obese volunteers and 23 volunteers of normal weight who participated in the Rockefeller study were hospitalized for periods ranging from weeks to months. While hospitalized, each was given a liquid diet containing a precise number of calories and combination of nutrients for as long as required to reduce their weight by 10%. The number of calories was then adjusted to find the amount required to maintain the weight loss, and that level was maintained for an additional eight weeks. Sophisticated techniques were used to measure how many calories they burned while at rest or while exercising.
Using similar techniques, researchers at Rockefeller and elsewhere had previously shown that the body's food requirement diminished during a diet. "But people believed that once you achieved a new, lower weight plateau, those requirements would return to normal," said Dr. Rudolph L. Leibel, who co-led the study with Hirsch. "That's not what we found."
In both the obese and normal weight groups, they found that each patient's so-called basal metabolism--the energy required to keep the body going when at rest--was lower than it was before the weight loss. More dramatically, the energy required for physical tasks was reduced even more. In short, they required less food to accomplish the same tasks.
To illustrate the effect, Leibel contrasted a hypothetical man who had weighed 150 pounds all his adult life and another 150-pound man who had formerly weighed 165 pounds. The man who had lost weight, he said, would have to eat 15% fewer calories to maintain that weight than the man who had always weighed 150 pounds.
Interestingly, the effect worked in the opposite direction as well. A 10% increase in body weight was accompanied by a 15% increase in food intake necessary to maintain the new weight. "This is a subtle difference," Leibel said. "It wouldn't have been observed" in people who were not hospitalized.
The results support the now widely accepted idea that each individual has a genetically determined set point, a metabolically "desired" weight that the body goes to great lengths to maintain. Researchers are looking for ways to change the set point permanently, he added, but have been unsuccessful.
The researchers also observed that at least in terms of controlling weight, what a person eats is irrelevant. "A low-fat diet may be healthful for a number of other reasons," Leibel said, "but a calorie of fat and a calorie of carbohydrate count the same in weight reduction." Unfortunately, 500 calories of junk food is not nearly as filling as 500 calories of vegetables. Food high in fat also tastes better, so you are more likely to eat more, he added.
"The take-home message," he said, "is that (obesity) is not a question of willpower or behavior. Maintenance of a new body weight will require indefinite attention to caloric intake. You will have to restrict calories . . . 15% more than we thought before. And you are also going to have to get more exercise."