The more we exercise, the better able we are to burn more fat, a finding that could ultimately lead to a pill that could mimic the effects of exercise.


Exercise boosts metabolism and lasts even after the workout ends.

People who are fitter burn fat more efficiently during exercise.

Potential applications include targeted fitness programs, better sports drinks and even a magic exercise pill.

Exercising boosts your ability to burn fat by anywhere from 50 percent to more than 1,000 percent, depending on how fit you are to begin with and how long you exercise, found a new study. What's more, this accelerated burn lasts long after the workout ends.

The study was the first to look in detail at how exercise affects more than 200 molecules in the body that are related to metabolism. Besides helping explain why exercise is good for us, the findings might lead to better tests for assessing fitness, new ways to diagnose heart problems, and better nutritional supplements that replenish what's lost during heavy exercise.

Eventually, the work might even inspire a magic exercise pill.

"This notion of changing metabolism by exercising is something that is very much confirmed by our paper," said Gregory Lewis, a cardiologist at Massachusetts General Hospital and Harvard Medical School. "Even after a 10-minute bout of exercise, when people's heart rate is back to normal and their blood pressure is back to normal and they're going about other activities, the metabolites that change during peak exercise persist for at least an hour afterwards."

"By virtue of taking the stairs at work or doing the treadmill for as little as 10 minutes, you're altering your metabolism for a significant period of time that extends beyond that period of exercise," Lewis said. "You're going from a fuel-storage to a fuel-burning state."

Along with a large group of colleagues, Lewis challenged 70 people to run on a treadmill to the point where they felt like they couldn't go on anymore. Blood samples were taken before the challenge, right when the runners reached their peak of exertion, and about an hour later. Sessions lasted an average of 10 minutes. Another eight people did the same kind of test on an exercise bike.

In the blood samples, scientists looked at a panel of more than 200 molecules that have something to do with metabolism. These metabolites included building blocks and breakdown products, like amino acids, sugars and vitamins. It also included reporter molecules like glucose, which reflects the breakdown of carbohydrates. Blood tests in standard exercise studies usually measure just seven metabolites.

Results, which appear today in the journal Science Translational Medicine, showed that both bikers and runners experienced changes in more than 20 metabolites, including a few that have never been associated with exercise. Some went down significantly. Others went up.

One of the most interesting shifts involved glycerol, which is a marker of fat metabolism. Glycerol levels rose during bouts of exertion in all of the exercisers. But how high the levels spiked varied from 50 percent in people who were lowest on the fitness spectrum to 100 percent in fitter participants. In a group of 25 athletes who ran the Boston Marathon, glycerol levels increased by more than 1,100 percent. In all of the groups, levels were still elevated an hour later.

The researchers don't yet know whether some people are born with metabolisms that respond better to exercise. But if it turns out that a fitness regime could help people burn fat more efficiently, the new work could lead to more accurate recommendations for exercise and new nutritional supplements. It could also address the long-standing question of how exactly exercise reduces the risk of heart disease and cancer, lengthens lives and promotes brain health.

"It's a huge question, because if we had a better idea of why exercise promotes long-term health and longevity, we could potentially get better at telling people what type of exercise to do and how to exercise," said Daniel Rader, a preventative cardiologist at the University of Pennsylvania.

"Perhaps most evocative of all, if we knew the pathways involved, we could potentially develop new drugs that target those pathways and mimic the effects of exercise," he added. "That's not to say that we could take pills instead of exercise, but it is to say that."