All Fat is Not Bad: Study Shows Exercise Creates “Good Fat”

June 21, 2013

Two new studies of mice and humans suggest that exercise can train fat to behave differently than the fat that develops from sedentary behavior, and that this "good fat" may elicit metabolic improvements in other tissues, according to research presented today at the American Diabetes Association's 73rd Scientific Sessions®.

The studies, funded by the American Diabetes Association and the National Institutes of Health, found that mice that ran on an exercise wheel for 11 days and men who underwent 12 weeks of training on an exercise bicycle underwent a browning of their subcutaneous white adipose tissue (SCWAT) that appears to have led to profound changes in the way that fat behaved in the body. The browner fat was more metabolically active than the white fat that results from sedentary behavior. 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 found that those mice showed increased glucose tolerance and insulin sensitivity for at least 12 weeks following transplantation.

“Our results showed that exercise doesn’t just have beneficial effects on muscle, it also affects fat,” said Kristin Stanford, PhD, a postdoctoral fellow at Joslin Diabetes Center in Boston. “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.”

Whether the browner fat is also having this impact in humans is not known at this point, since this type of transplantation study cannot yet be done in humans.

“We know that exercise is good for us,” added Laurie Goodyear, PhD, a Joslin section head who is senior investigator on the study and an associate professor at Harvard Medical School. “But what we’re showing here is that fat changes dramatically in response to exercise training and 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,” Stanford said.

These studies suggest that even if you’re not losing weight, exercise is still training your fat to be more metabolically active; even if you don’t see the results on the scale, you are still improving your overall metabolism and therefore your health.

About the American Diabetes Association

Nearly half of American adults have diabetes or prediabetes; more than 30 million adults and children have diabetes; and every 21 seconds, another individual is diagnosed with diabetes in the U.S. Founded in 1940, the American Diabetes Association (ADA) is the nation’s leading voluntary health organization whose mission is to prevent and cure diabetes, and to improve the lives of all people affected by diabetes. The ADA drives discovery by funding research to treat, manage and prevent all types of diabetes, as well as to search for cures; raises voice to the urgency of the diabetes epidemic; and works to safeguard policies and programs that protect people with diabetes. In addition, the ADA supports people living with diabetes, those at risk of developing diabetes, and the health care professionals who serve them through information and programs that can improve health outcomes and quality of life. For more information, please call the ADA at 1-800-DIABETES (1-800-342-2383) or visit Information from both of these sources is available in English and Spanish. Find us on Facebook (American Diabetes Association), Twitter (@AmDiabetesAssn) and Instagram (@AmDiabetesAssn)