FRIDAY, Sept. 4 (HealthDay News) -- For dieters, the benefits of exercise may go beyond calories burned, a new study suggests.
Exercise may ward off weight gain after dieting by reducing appetite, preventing fat cells from accumulating and by prompting the body to burn calories from fat before burning calories from carbohydrates, reducing feelings of hunger, research finds.
The study was published recently in the American Journal of Physiology -- Regulatory, Integrative and Comparative Physiology.
Researchers put obesity-prone rats on a high-fat diet for 16 weeks, during which time they ate whatever they wanted and did not exercise.
Later, rats were put on a low-fat, low-calorie diet to shed 14 percent of their body weight. Rats were then kept on the diet for eight weeks to maintain their lower weight.
During the maintenance phase, half the rats exercised on a treadmill while the other half were sedentary.
Afterward, rats were permitted to eat as much low-fat food as they wanted. One group continued to exercise while the other didn't.
After two months, the rats that exercised regained less weight, burned more fat in the morning and more carbohydrates later in the day, accumulated fewer fat cells and gained less abdominal fat compared to the sedentary rats.
Since less energy is needed to store fat than to store carbohydrates, burning carbohydrates first burns less calories overall, according to researchers from the University of Colorado Denver.
In rats that exercised, burning fat first may also help to dampen feelings of hunger.
Exercise also protected against the increase in fat cells that often occurs when weight is regained. While the sedentary rats accumulated new fat cells soon after they started regaining the weight, the rats that exercised didn't.
New fat cells increase fat storage capacity in the abdomen, according to the study. The increase in fat cells may also help explain why sedentary rats ended up heavier than even before they dieted.
Though weight gain seems to be clear-cut -- when more calories are consumed than calories burned, you gain weight -- research is showing that a person's body weight, appetite and metabolism are determined by an interplay of physiological, psychological, cognitive and lifestyle factors.
Previous research found that many dieters regain weight because calorie restriction can cause physiological signals, such as hunger, to go into overdrive, triggering overeating and weight gain.
Exercise may help in maintaining weight loss by altering what's known as "defended" weight, or the body weight each person's physiology and metabolism seeks to maintain, and may also make diets easier to follow, according to the study.The study also calls into question a widely accepted belief that the number of fat cells cannot be altered by dietary or lifestyle changes, researchers said.
The National Institute of Diabetes and Digestive and Kidney Diseases has more on obesity.
SOURCE: American Physiological Society, news release, Sept. 2, 2009