Irisin: What You Need to Know About the 'Exercise Hormone'

For many scientists and SoulCyclists, the Holy Grail of Biology is a weight-loss hack that makes all that sweating obsolete. That’s why when the discovery of Irisin, a beneficial hormone released during exercise, was first reported in 2012, many scoffed. It struck many pilates instructors and distance runners as improbable that a single molecule could do so much to alter our moods and bodies. The hormone was dismissed as a myth until last week when it was isolated. It’s back and it appears to be real.

A team from Harvard Medical School just published a study that “unequivocally” proves irisin’s existence and indicates that it increases the flow of blood, which leads to weight loss, improved cardiovascular health, and sharper cognition. That’s laudable science, but there’s no reason to expect Crunch Fitness to go out of business any time soon.

Irisin is thought to work by converting bad “white fat” — the stubbornly unburnable that gloms onto hips and stomaches — into “brown fat,” which the body burns up regularly to stay warm. The original study reporting its existence offered proof that mice and humans burned more calories as their Irisin levels increased. No changes in activity level or food intake were necessary to create observable results. Again, it’s not surprising that many scientists remained doubtful.

There’s no shortage of weight loss scams out there that claim to eliminate the need for humans to exert any physical effort ever, so it’s hard to blame the skeptics. As soon as Irisin came to the public’s attention, backlash was inevitable. Reports claimed the hormone didn’t affect humans and that efforts to measure it in the blood weren’t effective.

But Bruce Spiegelman, who led the Harvard study, stands by his ballsy claim that the elusive hormone is out there, lurking like a cryptid in our ventricles. “There is no next level of analysis,” he told The Scientist. “This is down to, literally, the atomic level.”

To detect irisin in the blood, Spiegelman’s team eschewed the less conclusive commercial kits used by other studies for tandem mass spectrometry, an incredibly sensitive method that allowed them to make their claim as close to irrefutable as a couch cowboy could hope.

The next step is to prove that Irisin does what we hope it does. While Speigelman’s study didn’t look into the original claims showing that increasing hormone levels in the body led to more calorie burn, there’s now renewed interest in finding out — to put it lightly. Anyone more interested in watching Netflix than circuit training should follow the next set of trials closely. This could be the ultimate fitness win, the one that doesn’t require anyone to break a sweat.