Exercise May Lower Risk of Diabetes and Obesity

A new study led by a team of researchers from Harvard Medical School and the Dana-Farber Cancer Institute, and published this week in the journal Nature, finds that a recently detected hormone called “irisin” which the body produces as a response to exercise may have the effect of reducing an individual’s risk of health issues such as obesity and diabetes, as well as changing regular white fat into the more beneficial brown fat.

Muscle Mice

The longstanding belief among scientists is that muscle cells exert an influence on biological processes in other parts of the body, not just the muscles themselves, and that the cells actually have a form of biochemical communication with fat.  However, the exact nature of the communication – including just what the cells “say” to the fat, and to what extent the communication is triggered or maintained by exercise – have long been uncertain, at least until the researchers looked closely at the behavior in rodent and human muscle cells of PGC1-alpha, a substance already known to be created by exercise in the muscles, and found that it can further stimulate exercise’s already considerable benefits.  They specifically bred mice whose muscles churned out unusually high levels of PGC1-alpha, and those mice were found to have a very strong resistance to aging-related diabetes and obesity, similar to the way that humans who get frequent exercise are resistant.

In the study, the team found that an increased muscle level of PGC1-alpha also triggers an increase of Fndc5, a protein which the biology field has long since detected without ever quite being able to figure what its purpose was.  The team observed that the protein actually broke up in several parts, including an unidentified hormone which the scientists named iris in honor of the Greek goddess of messengers, Iris.

While most matter that is born in a muscle tends to remain there, irisin instead uses the bloodstream to travel to fat cells, and in doing so, carries those aforementioned messages in the form of biochemical signals, the result of which is to turn white fat into brown fat.

The more commonly known white fat cells function as inert, unchanging, and often unsightly caches for fat, which brown fat cells are actually active on a metabolic level, using oxygen, needing energy and (perhaps most importantly) burning calories.  Up until 2009, brown fat was believed to be entirely depleted after infancy, but in recent years studies have been showing that adults do carry brown fat, though it varies from person to person.

Variance

And that variance may be dependent on the levels of irisin released during exercise.  Nature reports that the team also removed white fat cells from their study mice and injected the samples with irisin.  The cells began to show signs of browning, and the respiratory rates of the cells also showed signs of increasing, indicating that they were in fact burning more energy.

Studies on actual humans also showed an increase in irisin levels after a several-week program of intense jogging, and that the irisin was structurally identical in both mice and humans, thus implying that it’s a biologically crucially substance, hence remaining unchanged over eons.