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 shows that the body goes to remarkable lengths to maintain the weight you started your diet with.
It does so by slowing metabolism -- reducing the number of calories required for breathing, maintaining body temperature, circulating blood and even 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 and spent by subjects.
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 a regaining of the weight unless they eat less, increase their physical activity or both, he said.
The study suggests that a dieter who does not exercise will have to consume 15 percent fewer calories than researchers had previously believed in order to maintain the reduced weight. Those who do exercise can eat a little more.
The new results and other studies also should help to change the attitude of physicians, employers and others who castigate the obese for their overeating and lack of willpower, Dr. William I. Bennett of the Cambridge Hospital wrote.
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, and one that continues to grow. Today, one in every three people in this country is overweight, compared with one in every four in 1980.
The 18 obese volunteers and 23 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 percent. 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 the course of 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 Dr. 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.
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.
The researchers also observed that, at least in terms of controlling weight, what a person eats is irrelevant. "A low-fat diet may be healthy for a number of other reasons," Dr. Leibel said, "but a calorie of fat and a calorie of carbohydrate count the same in weight reduction."