Exercise is not just for weight loss and sport anymore. Recent studies show that as well as positively boosting our muscles, it changes quality of our fat. Just as we better understand cholesterol and the different effects of various fats, we’re beginning to grasp the fact that both good and bad fat are present within the body.
We also have evidence that exercise influences how fat in the body behaves. Two new studies of mice and humans, sponsored by the American Diabetes Association (ADA) and the National Institutes of Health and presented at the ADA’s 73rd Scientific Sessions, indicate that exercise turns on a host of metabolism-boosting genes in fat that improve glucose tolerance and mitigate the effect of a fatty diet.
“Most of the research has focused on how exercise or exercise training can affect skeletal muscle,” notes Laurie Goodyear, Ph.D., of the Joslin Diabetes Center in Boston. “Exercise doesn’t just affect muscle, it doesn’t just affect the heart, it actually affects probably every tissue in the body.”
Of Mice And Men
In one of these studies, mice ran on an exercise wheel for 11 days straight. In the other, physically fit men rode an exercise bike one hour per day, five days per week, for 12 weeks. In both cases, scientists found a browning of the subcutaneous white adipose tissue (SCWAT), the fat located under the muscles and not between muscle and skin. (The fat under your skin, the fat you can see, is a dangerous form of fat implicated in heart disease and diabetes.) In addition to the cardiovascular and muscular health benefits of exercise, the studies showed that exercise actually changes the quality of body fat, shifting the way it behaves.
In the animal study, researchers transplanted brown fat from the exercising mice into fat, sedentary mice who were filled with white fat. As a result, the brown adipose tissue made positive changes in the sedentary mice. For 12 weeks after they received the brown fat transplant, the sedentary mice enjoyed better glucose tolerance and insulin sensitivity. And when the fat mice were fed a high-fat diet that would have otherwise sharply increased their blood sugar, their blood sugar levels remained “significantly lower… suggesting the transplanted subcutaneous white adipose tissue exerted endocrine effects,” the researchers said.
These studies suggest that fat does not have to stay in a permanently harmful state. Instead, its gene expression can be changed. It can be trained to produce positive effects when you exercise and, thus, become good fat.
This change involves positive changes in metabolism, mitochondrial biogenesis, oxidant stress and signaling, and membrane transport. These changes, in turn, boost glucose tolerance, improve body composition, decrease fat mass and decrease the negative effects of a fatty diet.
Exercise may induce fat cells to secrete proteins that act as a signal for other tissues. “It’s clear that when fat gets trained,” notes Stanford, “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.”
This is great news for those who don’t exercise and eat a questionable diet: Simply exercising and getting your heart rate going faster for a time every week can lead to healthful changes in your body fat. Moreover, even if you don’t lose weight, your exercise regimen still improves your metabolism.