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Exercise makes your fat healthier

November 7, 2016 (Updated: August 16, 2018)
Lily Moran

This might scramble your sense of what your body’s made of…but let me introduce you to brown fat. Along with white fat, we’re born with fat that’s brown. It does wonderful work for us—burning calories, helping improve insulin and blood sugar levels, reducing the risks for type 2 diabetes, and adding huge benefits to exercise.

What is brown fat, and why is it good?

Our white fat serves essentially as a fuel depot, storing calories to use when needed. Brown fat plays a more active role. It’s loaded with mitochondria that burn those calories when we need energy.

We lose almost all of our brown fat as we age. That’s too bad, because the more we learn about it, the more promising it looks—on a number of major health fronts.

So new research on brown fat brings good news. It seems we can bring brown fat back into play—especially when the play is exercise.

A home-made, fat-fighting health hero?

Let me also introduce you to a hormone called irisin. It’s a relatively recent discovery that showed up in the muscle tissue of lab mice when they exercised.

A breakthrough study by the University of Florida in 2012 followed up on that discovery, and showed that when lab mice were injected with a prepared irisin formulation:

  • Irisin turned some of their white fat into the more active, calorie-burning brown fat
  • Irisin also seemed to keep the mice from becoming obese, even when they were fed a high-fat, high-calorie diet that should have puffed them up like little muffins

So it just had to be asked—what if irisin has the same effect on people as on mice? What if it makes white fat just…disappear? What if it reduces type 2 diabetes risk? What if it prevents obesity, even in the face of a high-fat, high-calorie diet?

Who could pass up the chance to chase those answers down?

Let the research roll.

For man or just mouse?

Of course, it first had to be determined whether irisin is even present in humans. Maybe the mice are keeping it for themselves?

Then, if it’s available and active in humans, would it affect human fat cells the same way as it did mouse fat cells?


  • One study found traces of irisin in sedentary people—but lots of irisin in people who exercised often.
  • Another study found that people with lower body mass indexes (BMIs), tended to have more brown fat. Low BMI is often associated with exercise, among other factors.

These confirmed that humans can produce irisin—and suggested a strong connection between exercise and increased levels of irisin.

But did it prove that irisin can do in people—convert white fat to brown—what it did in mice?

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One more step toward realizing a promise

Another study looked at both white and brown human fat from tissue extracted during surgery.

Some of the white fat cells were mature. Others were younger—essentially stem cells that could grow into mature fat cells or other types of tissue.

The researchers exposed both white and brown fat cells to varying strengths of irisin. They then looked for signs that the white fat was becoming brown fat.

And there the signs were—especially in the white fat cells that were exposed to moderate or high doses of irisin. Those cells began to act brown, becoming significantly more metabolically active—ready, willing, and able to burn calories, instead of retaining calories.

In other words, the study gave us significant evidence that irisin prompted “browning” of white fat. Which simultaneously led to increased metabolic energy and decreased formation of new white fat.

There was more:

  • Many of the young stem cells in the fat that was exposed to irisin became the kind of cell that matures into bone, rather than maturing into white fat cells.
  • In the end, the irisin-treated tissue contained about 40 percent fewer mature fat cells than tissue unexposed to the hormone—which showed no change.

Conclusion: yes, irisin can “disappear” existing white fat, and keep new white fat from developing.

Recommendation: exercise—it produces irisin

We’re still in the early days of learning about irisin. We’ve studied only human tissue samples, not live humans. So there’s still much we don’t know:

  • What types of exercise produce the most irisin?
  • How much irisin is enough?
  • If exercise produces irisin, and irisin reduces white fat, why do so many studies show that exercise alone rarely results in significant weight loss?

Dr. Li-Jun Yang, a professor of hematopathology at the University of Florida and an author of the breakthrough irisin study, is convinced that there’s a major payoff down the road.

While we travel that road, gathering more data on brown fat, irisin, and where they might do the most good, Dr. Yang says, “My advice is, exercise as much as you can. We know it’s healthy and now we’re beginning to understand better why.”

I couldn’t agree more.

So please, those of you trying to get healthier by exercising, but not seeing any weight loss, don’t be discouraged. If pounds are not lost, all is not lost—by a long shot.

These new insights into brown fat and its importance tell us that exercise can still do you a world of immediate and long-term good.


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