Good workout. A new study helps explain the link between exercise and weight loss.

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Good workout. A new study helps explain the link between exercise and weight loss.

Muscle Molecule Spurs Fat Cells to Slim Down

Just in time for all those New Year’s resolutions to exercise more, scientists have a better idea of how the body turns pain into gain. Exertion stimulates muscles to release a molecule that modifies fat cells, turning them into calorie-burning machines, a research team has found.

Exercise works the muscles but affects cells throughout the body, even in the brain. An important player in this process is a protein called PGC-1α. In exercising muscles, it activates genes that ramp up energy use. But its impact extends beyond these tissues. The protein somehow indirectly prompts, for example, white fat—the energy-storing variety that pads our hips and stomachs—to switch on genes that are characteristic of brown fat, a form that burns calories. PGC-1α doesn’t travel outside muscle cells, so researchers aren’t sure how its influence spreads, however.

By sifting through the secretions of PGC-1α-making muscle cells, Robert Gerszten of Harvard Medical School in Boston and colleagues have nabbed one molecule that might be doing the protein’s bidding: β-aminoisobutyric acid (BAIBA). They found that BAIBA induces white fat cells to become more like brown fat cells, altering their gene activity patterns. And it stimulates other cell types, stoking fat metabolism in the liver, the team also reveals today in Cell Metabolism.

These effects may translate into a healthier metabolism. When mice lapped up water laced with the molecule, the rodents lost weight and were better at absorbing glucose.

Does BAIBA produce similar modifications in humans? The researchers analyzed blood samples from more than 2000 subjects in the famous Framingham Heart Study, which has been probing the causes of cardiovascular disease for more than 60 years. The team found low BAIBA levels in people who had risk factors for heart disease and diabetes, such as high insulin and high cholesterol. In contrast, after couch potatoes taking part in a different study began an exercise program, the concentration of BAIBA in their blood jumped 17%, the researchers determined.

These findings suggest that BAIBA is PGGC-1α’s molecular emissary. But BAIBA isn’t the only such messenger. Two years ago, a group that included some of the authors on the current paper identified another example: the protein irisin. But because exercise triggers complex effects in multiple tissues and organs, “it’s no surprise that other factors could be found here,” says metabolic physiologist Christopher Newgard of Duke University Medical Center in Durham, North Carolina, who wasn’t connected to either the irisin or BAIBA research. “This paper is noteworthy, and this factor deserves further attention.” One question scientists should focus on, he says, is whether levels of BAIBA fall as people become obese.

It’s too early to say whether BAIBA can be developed into a drug that would help people lose weight or fend off metabolic diseases like diabetes and cardiovascular disease. “We are going to study it extensively in animals to see if there are any odd side effects we haven’t picked up,” Gerszten says. In the meantime, if you want to keep your New Year’s resolution, you should probably hold on to that gym membership.

Posted in Biology, Health