“We’re all told to exercise. In the end, presumably the effects will all come down to a series of molecules.” – Bruce Spiegelman, cellular biologist at Harvard Medical School.
What exactly is irisin? Irisin induces browning of white adipose tissues in vivo and protects against diet-induced obesity and diabetes. Bruce Spiegelman first discovered the hormone, named for the Greek messenger goddess Iris. The hormone has been applied in some animal studies, designed to increase energy expenditure after physical exercise and promote healthy metabolism. But now it is being tested with human blood applying a more sophisticated, regularly used analytical technique.
Why is brown fat so important? Read our previous article for more information.
Experiments to measure irisin in individuals who exercise have caused some bitter scientific disputes, leading some to believe that humans don’t produce it at all – until now.
In the study, the researchers discovered that exercise increases the body’s production of a metabolism-regulating protein, which in turn stimulates expression of a protein that can produce the new hormone, which is located in the outer membranes of muscle cells.
To dig deeper into details regarding the link between irisin and exercise, the study compared sedentary and active subjects. 6 people who had been on a 12-week aerobic exercise regimen had an average of 4.3 nanograms of irisin per milliliter of blood serum. 4 people with no such training had only about 3.6. While it’s not clear how the hormone affects cells and tissues at those levels, Spiegelman and other experts conclude that the serum concentration of insulin, which is an important regulator of blood sugar, is in a similar range.
The fact that irisin is produced at dramatically lower levels in humans than in other animals also can’t be ignored. “I’m still suspicious,” says biochemist Harold Erickson at Duke University in Durham, North Carolina. University of Oslo nutritional biologist Christian Drevon, who took part in the study suggesting lower human production of irisin, says the new approach could be an “improved method” for detecting the protein if validated in other labs. But he sees no convincing evidence that irisin is sensitive to exercise.
“That’s only because the exercise component of the study is weak,” Drevon says, with other researchers agreeing. The differences between trainees and sedentary people could be due to anything else other than irisin, they caution, and the experiment should have observed the same subjects both before and after exercise. Spiegelman concedes that the new work wasn’t a rigorous exercise study, but he says his lab will continue to probe the effects of irisin on the human brain, bone, and fat tissues. This only means that more research needs to be done before conclusive evidence can be produced.
While the studies need to be fine tuned, scientists are still plugging away at body related research and how exercise can affect us in positive ways. Who’s to say that Irisin isn’t the next big hormone that should be tested? As science progresses so does our view on health and fitness.