You know you'll lose weight if you exercise, but have you ever given any thought to why?

Thanks to a group led by a University of Florida Health researcher, we know quite a bit more about how the hormone irisin helps convert calorie-storing white fat cells into brown fat cells that burn energy. Irisin is the compound that surges when the heart and other muscles are exerted, and now we know that it also inhibits the formation of fatty tissue. The study is the first of its kind to examine the mechanisms of irisin’s effect on human fat tissue and fat cells.

How does irisin do what it does? The hormone appears to work by boosting the activity of genes and a protein that are crucial to turning white fat cells into brown cells, the scientists learned.  And by significantly increasing the amount of energy used by those cells, it has betrayed the role it plays in burning fat.

Likewise, the researchers learned that irisin suppresses fat-cell formation. Among the tested fat-tissue samples, irisin reduced the number of mature fat cells by 20 to 60 percent compared with those of a control group. That suggests irisin reduces fat storage in the body by hindering the process that turns undifferentiated stem cells into fat cells while also promoting the stem cells’ differentiation into bone-forming cells, the researchers said.

The data was gleaned from fat cells donated by 28 patients who had breast reduction surgery. The scientists exposed the samples to irisin and found a nearly fivefold increase in cells that contain a protein known as UCP1 that is crucial to fat “burning.”

“We used human fat tissue cultures to prove that irisin has a positive effect by turning white fat into brown fat and that it increases the body’s fat-burning ability,” said Li-Jun Yang, M.D., a professor of hematopathology in the University of Florida's College of Medicine’s department of pathology, immunology and laboratory medicine.

The group's findings have been published in the American Journal of Physiology — Endocrinology and Metabolism.

Now that we have tapped into the compound that that actually burns and suppresses fat in the human body, does that mean a weight-loss elixir is on the horizon? Yang doesn't completely count out the idea of turning irisin into a prescription medication, she said that is uncertain and remains a long time away.

“Instead of waiting for a miracle drug, you can help yourself by changing your lifestyle. Exercise produces more irisin, which has many beneficial effects including fat reduction, stronger bones and better cardiovascular health,” Yang said.