Exercise has many benefits for the body and mind but how the body triggers some of these benefits--like improving our metabolism--is unknown.
Earlier this year, researchers at Harvard Medical School identified a new hormone produced during exercise that helps turn energy-storing white fat into energy-burning brown fat. In doing so, it improved glucose control, insulin levels and led to weight loss.
The discovery has exciting potential for many metabolic health problems including obesity, metabolic syndrome and type 2 diabetes.
White vs. Brown Fat
White fat--commonly referred to as body fat--accumulates throughout the body but most notably around the hips, thighs, buttocks and midsection. Its purpose is to store fat until it is needed for energy later.
Brown fat is virtually the opposite in that these cells are full of mitochondria that burn fat.
In the Harvard study, the researchers found that exercise, in both mice and humans, stimulates a chain reaction that leads to the production of a previously unknown hormone they named “irisin.”
This hormone makes white fat act like the metabolically active brown fat which burns more calories.
Irisin levels rose by 65% in mice after three weeks of free-wheel running. In humans, 10 weeks of regular endurance exercise doubled irisin levels.
Irisin also improved glucose tolerance and insulin balance, suggesting that it may be helpful in treating diabetes.
To confirm that irisin was responsible for these benefits, the researchers injected a small amount of irisin into the muscles of sedentary adult mice that were obese and pre-diabetic. After 10 days of treatment, the mice had better blood sugar control and insulin levels and had lost a little weight—all without exercise.
Then the researchers conducted yet another test to prove their theory. They injected antibodies to stop the production of irisin in the mice and then put them through an exercise regimen. After 10 days, there were none of the previous improvements seen with the exercise program.
So does this mean that irisin may be “the ultimate diet pill” giving you a fat-incinerating metabolism without breaking a sweat? We’re still a long way from knowing that for sure. But even if it did help you burn fat, all the other benefits of exercise—including muscle strength, tone and endurance will still require physical effort.
Nonetheless, the irisin discovery clearly has therapeutic potential.
Harvard Medical School
Los Angeles Times