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Fit People Burn Fat Faster

Blood Molecules Reveal 'Metabolic Signatures' of Fitness, Heart Disease
By
WebMD Health News
Reviewed by Laura J. Martin, MD

June 2, 2010 -- Small molecules in the blood not only reveal the "metabolic signature" of fitness, but hint at how new sports drinks or drugs might help people more effectively burn fat.

Using new technology, Massachusetts General Hospital researchers Gary Lewis, MD, Robert Gerszten, MD, and colleagues tracked more than 200 small molecules in the blood.

The molecules are the end products -- metabolites -- produced as the body goes about its business of converting sugars, fats, proteins, and amino acids into energy.

When Lewis's team looked at the metabolite profiles of relatively healthy, middle-aged, overweight men and women before and after a prescribed 10-minute exercise stress test, they got a surprise. Those who were more fit had a very different metabolite profile than those who were not fit, revealing a "metabolic signature" of fitness.

"People who are more fit are able to mobilize the fuel source in fat better than those who are less fit," Lewis tells WebMD. "That is a very interesting finding. Certain individuals will burn fat much more robustly than others."

That goes tenfold for marathon runners. When the researchers analyzed blood metabolites in 25 people who had just run the Boston Marathon, they found that they had gone into an intense fuel-burning mode that consumed fat a thousand times more effectively. Interestingly, those with above-average finish times had fewer harmful metabolites in their blood than those who finished with below-average times.

The increased ability to burn fat and other fuels, even in normal people, continued for at least an hour after they stopped exercising. And fat burning wasn't the only positive effect. Exercise also acted like an antioxidant, reducing oxidative stress in the body.

Opposite findings come from studies of sedentary people. Lewis says their metabolic profile indicates that their bodies get better and better at storing up fat reserves.

"With exercise you tap into all these fuels in the body and put yourself into a fuel-burning mode," Lewis says. "Unfortunately, the balance in a lot of people is tipped toward over-storage mode and away from this marked metabolic response seen in even a short bout of exercise."

Fitness in a Bottle?

It's not yet clear from the studies what it is that makes a person more fit.

"What we still are sorting out is, are these fit people inherently different based on genetics -- people who are meant to be lean and who when they walk across the street burn more fat? Or by going to the gym three times a week, have they been able to alter their metabolism to burn fat more robustly?"

A tantalizing hint comes from further studies suggesting that the metabolites seen after exercise aren't just by-products of fuel burning. They may play an active role in promoting fitness.

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