Forget Being “Big Boned”—Are Your Bones Fat?

It turns out fat doesn't show up just on your belly or under your chin—it's actually in your skeleton.

Forget-Big-Boned--Are-Your-Bones-Fat-197985785-Puwadol-JaturawutthichaiPuwadol Jaturawutthichai/shutterstockDo you have flabby bones? If you’re obese, you might. And it can cause your bones to be weaker than normal.

The solution, according to a new study, is to exercise. Beyond all the benefits of exercise you already know well, working out can also improve bone quality within a few weeks of beginning a workout regimen, as it burns fat in the bone marrow.

The study, published in the Journal of Bone and Mineral Research, revealed that obese individuals, who typically have worse bone quality, may derive greater health benefits from exercise than their lean peers.

For their work, the team of researchers fed obese mice a high-fat diet for three months, and fed control mice a normal diet. Though research in mice cannot be directly translated to the human condition, the findings prove valuable, considering the types of stem cells that produce bone and fat in mice are the same as those that produce bone and fat in humans.

Both groups of mice were exercised on running wheels for a six-week period. “Mice love to run so this is easy to do,” said lead author Maya Styner, MD, a physician and assistant professor of endocrinology and metabolism at the University of North Carolina at Chapel Hill. In allowing them to run as much as they desired, the team found that both the lean mice and the obese mice ran similar daily distances and times, with each mouse running an estimated five miles per day.

After the experiment, the researchers analyzed the animals’ body composition, marrow fat, and bone quantity, using various imaging and molecular techniques. The team found that the obese mice started out with more fat cells and larger fat cells in their marrow, but after exercising for six weeks, they showed a significant reduction in the overall size of fat cells as well as overall amount of fat in their marrow. In fact, their marrow fat post-exercise looked almost identical to the marrow fat of the lean mice who exercised.

The running turned out to be a powerful fat-burner and bone-builder for the obese mice, with their number of fat cells dropping by more than half in the ones that exercised, compared to obese mice that were sedentary. (There was no reported change in fat cells among the lean mice.) “We found that the fat within the bone is responsive to running and decreases in size—like abdominal fat, and that this goes along with significantly improved bone density,” Dr. Styner told Reader’s Digest. “We found evidence that there is an increase in the use of fat calories in bone during exercise and that the obese mice benefited even more than the lean mice.”

According to Dr. Styner, such results suggest that marrow fat is capable of being burned off through exercise, significantly benefiting bone health. “This study demonstrates that for bone health and strength, obese exercisers get the most benefit compared with lean exercisers, as obese exercisers build more bone than lean exercisers,” she says.

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