Casey Kristin Frye
Jan 11, 2012

Irisin hormone mimics benefits of exercise with brown fat

In modern America, it is not unusual for a restaurant chain to sell triple patty, greasy, drool-inducing burgers, replete with bacon and condiments, for just a few dollars. Meanwhile, most citizens lead a sedentary lifestyle, working office jobs that require no more physical activity than moving fingers around to type on a keyboard and use a mouse. After driving home or taking public transportation, they relax in comfy, snack-packed homes where the couch beckons them to sit in front of a television.  Is it any wonder, then, that America has one of the highest obesity rates in the world?

Sure, we all try to eat a healthy, low calorie, high fiber diet and/or increase our physical activity, all in the name of losing that stubborn fat, but it never seems to work. Fat, whether it clings unyieldingly to our bodies or clogs our arteries, seems to present a never-ending supply of bad news … or does it?

White fat, scientifically known as white adipose tissue, is responsible for causing flabby arms and a belly that hangs below the belt. In other words, white fat is what stores the extra calories we consume. There is another fat, however, that is considered good. Just as bad LDL cholesterol has its good counterpart, HDL cholesterol, white fat has its good counterpart in brown fat.

Though it is hard to believe that there could be such a thing as "good fat," brown adipose tissue differs from white fat because it has large amounts of mitochondria and capillaries. Its evolutionary purpose is to generate heat to keep the body warm by burning excess calories, which are primarily stored in the form of white fat. Bears are a solid example of this. Before hibernating, a bear will stuff its body with calories. Then, while it slumbers in its cave, the bear’s brown fat will burn away the white fat.

While brown fat is abundant in newborns, adults have relatively small amounts of brown fats. Wouldn't it be nice if we could gain a bit more of this good fat?

Luckily, researchers at the Dana-Farber Cancer Institute have discovered a naturally present hormone that can turn white fat into brown fat, for those of us who wish to lead less lazy lifestyles.

This newfound hormone, irisin, whose namesake is the Greek messenger goddess Iris, has been proven to have a direct influence over adipose. This hormone is why exercising is so beneficial to our bodies; an increase in exercise yields higher amounts of irisin.

When the hormone was injected into mice, there was a notable response. Not only did irisin stimulate the conversion of white fat into brown fat, it also improved how quickly glucose was removed from the blood.

Scientists wanted to see just how effective irisin could be in mimicking the benefits of exercise, so they injected significant amounts into mice who were overweight and prediabetic. Much to their surprise, the mice had greater control over their blood and insulin levels, and experienced a decrease in weight.

"It's exciting to find a natural substance connected to exercise that has such clear therapeutic potential," said the study’s first author, Dr. Pontus Bostroöm. He also commented that while irisin does mimic exercise, it cannot fully replace a workout regimen.

This hormone seems too good to be true, so there has to be some adverse side effect, right? Wrong! According to the study, there were no reports of toxicity or harmful side effects. Scientists who took part in the study affirmed this was to be expected; they say their predictions were correct because irisin’s presence and level increase can all occur naturally.

Scientists are confident that an irisin drug will speed to the clinical trial stage within the next two years not only because mice protein models are identical to humans, but also because irisin occurs naturally in the body.

Until then, research is being continued to see how beneficial, if at all, the hormone will be in treating metabolic and neurodegenerative diseases such as diabetes, insulin resistance, obesity and Parkinson’s disease.