Researchers discover a fat-burning hormone—you may already have it, from the Harvard Health Letter

A hormone released by muscles during exercise transforms white fat cells in the body into brown fat cells, reports the June 2012 Harvard Health Letter. The hormone, known as irisin, also appears to help prevent or overcome insulin resistance, a condition that leads to type 2 diabetes.

White fat cells simply store fat. Brown fat cells, in contrast, actually burn fat. And brown fat cells keep burning fat even after you've stopped exercising.

"Irisin travels throughout the body in the blood and alters fat cells," explains Dr. Anthony Komaroff, editor in chief of the Harvard Health Letter. "If your goal is to lose weight, you want to increase the number of brown fat cells and decrease white fat cells."

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