The Associated Press

TORONTO People who exercise and then reach for extra snacks may not lose weight, but they still alter their body chemistry in a way that burns up more fat, a researcher reports.

Dr. Jorge Calles, an endocrinologist at the University of Vermont, offered what he called the first carefully controlled study to show that fat burning increases significantly with exercise even if people overeat.

It's well known that people burn more fat if they begin to exercise and also keep their food intake constant.

Calles reported his findings Tuesday at the Seventh International Congress on Obesity.

The study supports the idea that exercising can help people lose weight. That might seem obvious, but it has been the subject of debate among obesity specialists, Calles said.

"There's no question about the cardiovascular benefits, and no question exercise is helpful for people with diabetes," Calles said. "But for treatment of obesity, there is a debate.

"We are beginning to show that indeed exercise can be beneficial."

Dr. Richard Atkinson, an obesity specialist at the University of Wisconsin, said that individual variations in fat burning help explain why some people seem to be able to eat a lot without gaining weight, while others put on weight much more easily.

Calles' findings are an important part of the argument that exercise can help people lose weight, said Atkinson, who also attended the conference.

Calles' study involved 20 people. Some were overfed 1,000 calories per day without being allowed to exercise, while others were overfed and assigned to do just enough exercise to compensate for the excess calories.

In those who were over fed without exercise, the amount of fat burned dropped from the equivalent of 518 calories per day to 97 calories per day. The burning of carbohydrates rose.

In those who were overfed and who exercised, fat burning rose from the equivalent of 406 calories per day to 685, while the burning of carbohydrates fell.

In a separate study, John Blundell and colleagues at the University of Leeds in England found that exercise can produce a suppression of appetite that can lead to weight loss. But they also found that people who exercise must also watch the fat content of their diets, because high-fat foods can completely overwhelm the beneficial effects of exercise.

Blundell and his colleagues then offered subjects a choice of either high-fat foods or high-carbohydrate foods after exercising. In an encouraging sign, they found that the subjects had no special preference for high-fat foods after they had exercised.

Calles acknowledged that the numbers of people in his study were small. Read Next Article