Duh

Exercise is good for you. Here's another reason, in case you didn't believe everything everyone's been saying for the last 40 years. Exercise turns bad, white fat cells into brown fat cells (which aren't just big clumps of stuff that take up space, but are active and use energy and metabolize), once thought to cease to exist in the human body after babyhood. I never knew "babyhood" was a word. But it makes sense. It's because exercise promotes the creation of something called PGC-1 alpha, recently dubbed "irisin," a protein that continues to benefit the body even once exercise has ceased.

http://well.blogs.nytimes.com/2012/01/11/exercise-hormone-helps-keep-us-healthy/?ref=health

But how muscle cells “talk” to fat, what they tell the fat and what role exercise has in sparking or sustaining that conversation have been mysteries — until, in the new study, scientists closely examined the operations of a substance called PGC1-alpha, which is produced in abundance in muscles during and after exercise.

“It seems clear that PGC1a stimulates many of the recognized health benefits of exercise,” said Bruce Spiegelman, the Stanley J. Korsmeyer professor of cell biology and medicine at the Dana-Farber Cancer Institute and Harvard Medical School, who led the study. Mice bred to produce preternaturally large amounts of PGC1a in their muscles are typically resistant to age-related obesity and diabetes, much as people who regularly exercise are.

But never fear, you who are exercise averse or immobilized from disease or injury -

In upcoming experiments, Dr. Spiegelman plans to study whether injections of irisin imitate some of the metabolic benefits of exercise in people who, because of disease or disability, cannot work out. He also hopes to elucidate just how much and what types of exercise produce the greatest natural irisin increases in healthy people.