But for mere mortals -- folks who are simply trying to keep their weight in check or stave off heart disease -- adding calories right after burning them up could negate the benefits of the sweat, researchers say.
"If people are going to go out and exercise to benefit their health, they should not be eating back the calories immediately upon finishing, or within a couple of hours of finishing," said Barry S. Braun, director of the Energy Metabolism Laboratory at the University of Massachusetts Amherst. "In order to maintain the benefits, you need to be in this calorie deficit."
"Athletes are always advised to do exactly the opposite," he continued. "That's great for athletes, but for the other 99.9% of the world, that's probably the wrong thing."
Braun is co-author of two papers appearing in the Journal of Applied Physiology, Nutrition and Metabolism and one paper published in the Journal of Applied Physiology that detail the findings.
Ten young, overweight men and women participated in each experiment.
For the first study, volunteers were asked to walk on a treadmill for an hour a day, burning about 500 calories each time. Half of the group were given a high-calorie carbohydrate drink immediately after their workout while the other half abstained.
Exercise increased insulin efficiency by 40% in those who did not eat afterwards. But the benefit was completely wiped out for those who had a high-carb drink after sweating.
These results had the researchers wondering if the type of calorie would make any difference.
For the second study, volunteers cycled for 75 minutes. Immediately after exercising, half of the participants ate a meal high in carbohydrates while the other half ate a meal low in carbohydrates but containing the same number of calories.
The ability of insulin to clear sugar from the blood was greater among people who ate the low-carb meal, the researchers found.
"It seems as though giving people back carbohydrates blunts or diminishes this exercise benefit," Braun said.
The third study was all about timing. Participants were given identical meals before, immediately after or three hours after cycling for 75 minutes.
The effectiveness of insulin was about the same no matter what the time, the study revealed.
"That really didn't make a whole lot of difference, which surprised us," Braun stated. "What did seem to matter was whether you ate back calories, and whether those calories were mostly carbohydrates."
SOURCES: Barry S. Braun, Ph.D., associate professor, kinesiology, and director, Energy Metabolism Laboratory, University of Massachusetts, Amherst; Jim White, R.D., personal trainer, registered dietitian and national spokesman, American Dietetic Association, Virginia Beach, Va.; 2008 and December 2005 Journal of Applied Physiology; 2007 Journal of Applied Physiology, Nutrition and Metabolism
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