Exercise makes cells burn extra energy—that's one way it helps control weight. It also generates a newly discovered hormone, called irisin, that transforms energy-storing white fat cells into energy-burning brown fat cells. Irisin also appears to help prevent or overcome cellular changes that lead to type 2 diabetes.
"Irisin travels throughout the body in the blood and alters fat cells," explains Dr. Anthony Komaroff, editor in chief of the Harvard Health Letter, in the June 2012 issue. "If your goal is to lose weight, you want to increase the number of brown fat cells and decrease white fat cells."
Fat "color" makes a difference
White adipose tissue, more commonly known as body fat, is the tissue that dimples thighs, enlarges waists and derrieres, and pads internal organs. Each white fat cell stores a large droplet of fat. Brown fat, in comparison, is chock full of energy-burning mitochondria. Its main function is to generate body heat by burning fat.
Babies are born with brown fat, but it was thought to gradually disappear. In 2009, several studies showed that adults still have brown fat cells lurking in their bodies. Earlier this year, a team led by Dr. Bruce Spiegelman, professor of cell biology and medicine at Harvard Medical School, identified irisin in mice and humans. His team also showed how irisin transforms white fat cells into brown ones, at least in mice. The same thing is likely to happen in humans, too, but that remains to be worked out.
This transformation helps the body burn more energy during exercise. The effect lingers, since brown fat cells keep burning fat even after you've stopped exercising. In addition, Spiegelman's work showed that irisin also helps prevent or overcome insulin resistance, which leads to type 2 diabetes.
No need to wait
The possibility of creating a new medication based on irisin for weight loss or type 2 diabetes may have pharmaceutical companies already mapping out the long, expensive process for bringing a new drug to market. But you can make your own irisin today, for free, by exercising. And even if irisin's effects aren't quite as potent in humans as they are in mice, you are still getting all the other benefits that exercise has to offer.