Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, March 9, 1995 TAG: 9503090100
SECTION: NATIONAL/INTERNATIONAL PAGE: A-1 EDITION: METRO
SOURCE: Associated Press
DATELINE: BOSTON NOTE: BELOW LENGTH: Medium
The hardest part of a diet is keeping off the weight. Now researchers believe they know why: The body simply burns up less energy after a weight loss.
Indeed, it turns out that a newly slender person uses considerably fewer calories than does someone exactly the same size who has always been slim. Even exercise does less good after a diet.
The result of this parsimony is almost inevitable. After a diet, people eat reasonable meals, get modest exercise and still grow fat. Even though they think they are watching their diets - and probably are - they still eat more than they need.
This does not mean keeping weight off is impossible, only that it is very, very difficult. It requires eating no more calories than are burned, and that means a lifelong commitment to modest eating and regular exercise.
While it may seem like grim news for overweight people, Dr. Rudolph Leibel sees a bright side.
``It suggests that the maintenance of body weight is a biological phenomenon, not solely a voluntary activity,'' he said.
In other words, obesity is not necessarily a badge of gluttony and sloth. It's natural.
Leibel and his colleagues at Rockefeller University in New York believe they have found an internal control that tries to keep body fat at a reasonably constant level. This level differs from person to person, and no one knows how an individual's fat target gets set.
The body does this by adjusting its metabolism - the rate at which it burns up calories - in response to both weight loss and gain. When someone takes pounds off, the metabolism slows. When they put it on, their metabolism burns food more quickly.
Either way, the body tends to try to get back to a particular level of fatness, what some diet experts call the set point.
The latest work results from a study of 18 overweight volunteers and 23 people who had never been obese. The results, published in today's issue of the New England Journal of Medicine, show that the fat and the lean alike respond to weight changes the same way.
When they lose 10 percent of their body weight, their bodies compensate by burning up 15 percent fewer calories than would be expected. When they increase their weight by 10 percent, they use up 15 percent more calories than would be expected.
About 60 percent of the body's energy is used to keep the heart pumping, the lungs breathing, the cells working and other internal housekeeping, what's called the resting metabolism. Another 10 percent is used for digestion. The final 30 percent is the energy burned up in physical activity.
The researchers found that when people gain weight, they burn up more calories during physical activity than would be expected for people their size. But their resting metabolisms are the same.
When they lose weight, however, the energy consumed by both their resting metabolism and exercise go down. Somehow, their muscles become more efficient.
by CNB