BOSTON – June 21, 2013 – Joslin Diabetes Center scientists have demonstrated through two new studies of mice and humans that exercise can train fat to behave differently than the fat that develops.

“Our results showed that exercise doesn’t just have beneficial effects on muscle, it also affects fat,” said Kristin Stanford, Ph.D., a post-doctoral fellow at Joslin Diabetes Center, who presented the results at the American Diabetes Association’s 73rd annual Scientific Sessions. “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.”

The American Diabetes Association and the National Institutes of Health funded these studies, which also exhibited that mice who ran on an exercise wheel for 11 days and men who underwent 12 weeks of training on an exercise bicycle experienced a browning of their subcutaneous white adipose tissue (SCWAT) that appears to have led to overwhelming changes in the way that fat behaved in the body. The browner fat was found to be more metabolically active than the white fat that is produced from sedentary behavior. In order to determine whether the browner fat could affect how the body uses glucose, researchers transplanted the trained mouse fat into high-fat, sedentary mice and discovered that those mice showed increased glucose tolerance and insulin sensitivity for at least 12 weeks following transplantation.

Since this type of transplantation has only been performed in mice, it is still unknown if the browner fat is having the same impact in humans. However, Joslin researchers are aware of the positive benefits of exercise for the body as a whole.

“We know that exercise is good for us,” explained Laurie Goodyear, Ph.D., Senior Investigator on the study, Head of the Section on Integrative Physiology and Metabolism at Joslin and an Associate Professor of Medicine at Harvard Medical School. “But what we’re showing here is that fat changes dramatically in response to exercise training, and it is having good metabolic effects. This is not the fat that’s around your middle, which is bad fat and can lead to diabetes and other insulin resistant conditions. It’s the fat that’s under the skin, the subcutaneous fat that adapts in a way that appears to be having important metabolic effects.”

The studies suggested that the browner fat was associated with increased glucose uptake, improved body composition, decreased fat mass and increased insulin sensitivity in mice. 

“Our work provides greater motivation than ever to get out there and exercise,” said Stanford.

These studies indicate that regardless of weight loss results, exercise is still training fat to become more metabolically active. This means that people who exercise are still improving their overall metabolism, and therefore, they are improving their overall health.