Many of us may not realize that body fat can be metabolically healthy, or the other way around, regardless of a person’s weight or shape.
“Healthy fat is not about how much fat” someone has, said Jeffrey Horowitz, a professor at the University of Michigan who studies exercise and metabolism. It’s about how well that fat works, he said. “A person who has healthier fat is much better off than someone with the same body fat percentage but whose fat is unhealthy.”
The main thing that differentiates healthy from dysfunctional fat, Horowitz continued, is the size of the fat cells. “The more small fat cells, the better,” he said.
And, notably, you don’t have to lose weight or fat to make the body fat you already have metabolically healthier.
Why does the size of fat cells matter?
Large fat cells, he said, are already full of fat. They can’t store much more and tend to leak some of their overloaded contents into the bloodstream in the form of fatty acids. From there, the fatty acids are released and lodged in other organs, such as the heart, muscles or liver. Fatty, well-marbled livers, muscles, or hearts are undesirable (unless, perhaps, you raise steers).
Small fat cells, on the other hand, can expand, essentially sipping fat from your blood. You want the fat to stay inside the fat cells, Horowitz said.
Healthy fat cells also contain lots of active mitochondria, the energy centers of any cell. Mitochondria convert oxygen and food into cellular energy. In general, the more mitochondria, the healthier and more resilient any cell, including fat cells, will be.
Finally, healthy adipose tissue is packed with blood vessels, to carry oxygen and nutrients to fat cells, along with battalions of other cells, most of them immune-related, that help fight inflammation. Without sufficient blood supply and immune protection, adipose tissue often becomes inflamed and scarred, releasing substances into the bloodstream that initiate similar, unhealthy inflammation in other parts of our bodies, even in people who are not overweight.
How exercise can reshape your fat cells
Until recently, however, scientists weren’t sure if or to what extent our fat might change. Namely, they knew that healthy adipose tissue could deteriorate, becoming filled with large, leaky cells, dysfunctional mitochondria, and inflammation.
But it was not clear whether this process could be reversed or slowed down. Some encouraging studies in recent years with rodents suggested that physically active animals harbored metabolically healthier body fat compared to sedentary rodents, even if they were all overweight by rodent standards.
But we are not laboratory mice, and many questions remain about the malleability of our body fat.
A to study However, published in June brought glimmers of clarity. In the study, researchers at the University of Copenhagen in Denmark took biopsies of abdominal fat from sedentary young men, sedentary older men, and physically active older men, most of them frequent and long-term cyclists.
Fat cells from sedentary older men showed relatively poor mitochondrial health, with fewer mitochondria than fat from young men and less energy produced by each mitochondria. But the fat cells of physically active men contained many mitochondria, even more than in the fat tissue of young men, so their fat cells were generally better supplied with energy. Their fat tissue also showed fewer signs of early inflammation than fat from inactive men, regardless of their age.
“Physical training meant more mitochondria and better-functioning mitochondria” and, in essence, healthier fats, said Anders Gudiksen, a professor of cell biology at the University of Copenhagen, who led the study.
But for anyone who hasn’t had the foresight to be a cyclist for life, another new study offers hope that starting exercise now, no matter how sedentary you’ve been, could quickly improve your fat guy’s fitness.
for the new to studypublished in the Journal of Physiology and supervised by Horowitz, researchers took biopsies of fat tissue from 36 sedentary men and women with obesity and then had them ride a stationary bike at a moderate pace for 45 minutes or more intensely for interval training. 20 minutes four times a week for 12 weeks.
The volunteers’ diets were carefully monitored so that they did not lose weight. Otherwise, Horowitz said, the changes in your fat tissue could be due to weight loss, not exercise.
But without losing pounds, the volunteers who exercised still regained their weight. They ended up with substantially more small fat cells, as well as more capillaries to nourish those cells. Their fat tissue also contained fewer biochemical markers of inflammation and fewer symptoms of scarring and hardening around the fat cells.
These effects were seen whether the volunteers rode moderately or intensely. “The intensity didn’t matter,” Horowitz said, just that they were active.
In the short term, these alterations should make adipose tissue better able to absorb and store the excess calories someone eats with large meals during the holidays, Horowitz said, a scenario that doesn’t necessarily mean weight gain. This fat is usually stored temporarily and is soon converted into energy for other tissues, such as muscle. But in the meantime, he said, it’s best to store that fat in fat cells, not the liver or arteries.
The long-term implications of exercise and fat revolve around inflammation, Horowitz said, and whether metabolically healthy fat contributes to a metabolically healthy body, and perhaps especially, whether people are obese.
We need more research to fully understand what constitutes healthy fat, he said, and the types and amounts of exercise that best build or maintain it. But it already seems clear, she said, that movement benefits fat as well as the rest of your body, offering one more reason to bike, walk, jog, swim or however you choose to be active today.
Do you have a fitness question? Email [email protected] and we may answer your question in a future column.
