Long-term exercise makes fat better at burning calories, but doesn’t turn it brown

Written by 
Jessica Moore
woman swimming on her back

Brown fat is good, white fat bad. That’s the impression given by recent metabolism research focused on how to make white fat, which stores energy, more like the rarer brown fat, which burns energy. However, a new study from the Florida Hospital Translational Research Institute for Metabolism and Diabetes (TRI-MD), an affiliate of Sanford Burnham Prebys Medical Discovery Institute (SBP), suggests that with regular exercise even white fat can be cajoled into burning more calories.

“Our findings reveal that even though exercise doesn’t turn white fat ‘beige’—that is, make some of it behave similarly to brown fat—it still has beneficial effects on metabolism in that tissue,” said Lauren M. Sparks, Ph.D., adjunct professor in the Integrative Metabolism Program at SBP in Lake Nona and an investigator at the TRI-MD. She led the research, recently published in the journal Obesity.

Prior to this investigation, not much was known about how exercise shapes the way human fat cells burn energy. One study suggested that endurance training does not change metabolism in white fat, but the experiments only assessed markers of ‘browning’. Sparks’ team aimed to examine the question more comprehensively by looking not only at browning markers, but also heat generation and the means by which most cells use energy—oxidizing fuels in mitochondria.

The researchers, including SBP’s Steven R. Smith, M.D., scientific director of the TRI-MD, compared the abdominal fat of people who work out at least four hours per week at moderate to vigorous intensity to that of sedentary individuals. The levels of mitochondrial oxidation markers were higher in the fat of active people compared with the inactive group, the scientists found, However, markers of heat generation and conversion to ‘beige’ fat were similar between the groups.

“This work highlights the importance of studying metabolism in humans,” Smith said. “Because exercise training in rodents does cause white fat to burn calories as heat, these animals may not be ideal models for answering these kinds of questions.”

“Understanding the effects of exercise on metabolism at the molecular level is critical,” Sparks said. “It connects the dots between physical activity and disease, and it could help refine exercise programs that help people with metabolic problems such as type 2 diabetes and obesity get healthier.”

The paper is available online here.