Not all of our fat is bad; in fact the metabolically active type commonly called "brown fat" is good for us. It promotes the burning of calories to maintain our core body temperature – while "white fat," on the other hand…just makes you fat. The good news is that exercise might actually help train white fat to become brown fat. New research presented at the American Diabetes Association meeting on June 21, 2013, showed that 10 healthy men who exercised for 12 weeks on a stationary bicycle converted some of their white fat stores to a healthier profile. A second study showed that the brown fat taken from active mice that ran on an exercise wheel for 11 days and transplanted into sedentary mice led to improvements in glucose tolerance and insulin sensitivity that lasted for at least 12 weeks after the transplants. Everyone is born with plenty of brown fat - it keeps body temperature stable in infants, but these new studies suggest that exercise can help create brown fat that has positive effects on health and may help prevent diabetes. "It's clear that when fat gets trained, it becomes browner and more metabolically active. We think there are factors being released into the bloodstream from the healthier fat that are working on other tissues," said researcher Kristin Stanford, Ph.D. of the Joslin Diabetes Center in Boston.
“All Fat Is Not Bad: Study Shows Exercise Creates ‘Good Fat’”, American Diabetes Association, press release, accessed June 24, 2013. http://www.marketwire.com/press-release/all-fat-is-not-bad-study-shows-exercise-creates-good-fat-1804671.htm