To explore the effects of years of regular exercise on fat tissue, researchers compared two groups of adults with obesity — 16 people who reported exercising at least four times a week for at least two years, and 16 who had never been physically active on a regular basis.
Each exerciser was matched to a non-exerciser of the same sex who had the same body fat percentage and weight.
Investigators analyzed samples of belly fat tissue from just under the skin and found that the fat from exercisers displayed some key differences compared with their sedentary peers:
- More capillaries (small blood vessels), which can also improve fat tissue’s ability to manage and store fat, along with more beneficial proteins that help with fat metabolism
- Lower inflammation, shown by fewer inflammatory cells called macrophages
- Reduced fibrosis, meaning that the fat tissue was healthier and less rigid
These results show that exercising regularly for an extended period of time seems to change fat tissue. If or when physically active people experience weight gain, it translates to more “healthy” fat in the midsection, rather than “unhealthy” fat around the organs (called visceral fat) or in the organs themselves, like the liver or heart.
Many people are confused or underwhelmed by the idea that they will be able to “store fat more effectively” or even think it’s a bad thing, says Jeffrey Horowitz, PhD, a professor of movement science at the School of Kinesiology at the University of Michigan in Ann Arbor.
“We’re not saying that exercise will cause people to gain more weight or fat. It’s important to note that increasing the capacity to store fat does not equate to gaining fat, which requires consuming more calories than you are expending,” says Dr. Horowitz.
Fat’s Role in How the Body Functions
The primary function of fat is to safely store extra energy that can be readily used by the body when needed, explains Laura den Hartigh, PhD, a researcher and assistant professor of medicine at UW Medicine Diabetes Institute in Seattle.
Having fat that is able to efficiently store that energy is a good thing, because if any excess energy cannot be stored properly within fat, it is likely to be stored in and around other organs, like the heart, liver, and muscle, says Dr. den Hartigh, who wasn’t involved in the research.
“These organs are not properly equipped to handle excess lipids (fats), which can lead to inflammation, insulin resistance, and high blood lipid levels, ultimately increasing a person’s risk of developing heart disease or diabetes,” she says.
Healthy fat tissue, which can store fat more effectively by expanding when needed, will protect these other internal organs from having too much extra fat, explains den Hartigh.
Healthier Fat May Reduce the Risk of Chronic Diseases
One disease caused by unhealthy fat accumulation is nonalcoholic fatty liver disease — now called metabolic dysfunction–associated steatotic liver disease (MASLD) — according to the authors. People who are overweight or have obesity are at higher risk for the disease, which happens when excess fat builds up in the liver. It’s estimated that about 25 percent of Americans have the condition.
Overall Health and Healthy Fat Are More Important Than BMI and Body Fat Percentage
This study shows that a person’s body weight and fat mass are less important than how healthy our body and fat are, says den Hartigh.
“Fat needs to be metabolically flexible in order to be healthy, and this study showed that those who regularly engage in aerobic exercise have more flexible fat, with a higher capacity to store and metabolize excess energy,” she says.
Horowitz says that exercise needs to be reframed as a way to be healthy, and not just as a way to help with weight loss.
Physical Activity Provides Benefits That Go Beyond the Scale
This study provides more evidence of why living a physically active lifestyle is good for us, even if we don’t get down to our high school body weight or whatever the weight loss goal is, Horowitz says.
“Many times people who exercise regularly and don’t hit those goals throw up their hands and say, ‘Oh, I guess I’m not just one of those people,’ and they think — incorrectly — that the activity isn’t really making a difference. But you are ‘one of those people,’ because you’re reaping the benefits,” says Horowitz.
While weight is an important issue, he adds, it’s a separate issue.
“By maintaining a physically active lifestyle, you’re improving your heart health, you’re helping manage blood sugar, you’re strengthening your bones and muscles, and this study shows you’re also improving the health of your fat tissue, which could reduce the risk of many chronic diseases,” says Horowitz.
This is excellent news, and another health benefit to encourage people to get regular physical activity, says Harry Stafford Jr., MD, a primary care sports medicine doctor at Duke Health in Durham, North Carolina, who was not involved in the study.
“We know patients who exercise do better than patients that don’t for multiple reasons. In many cases, people who are active will have a lower body weight, but this shows that there are benefits even when those results don’t show on a scale,” he says.
