Did you know that fat cells can be either white or brown and that each type has a different function?

White fat is the type we typically think of when we think of fat cells.  This white fat has, as one of its primary jobs, the ability to insulate us.  This is the fat many of us don’t like when we look in the mirror.

Brown fat, on the other hand, has the unique ability to generate heat and therefore burns energy.  A study from several years ago found that when these brown fat cells were destroyed, mice became obese.  So, is there a way to increase this brown fat?  (One interesting way to increase brown fat is simply by being cold; this causes so-called thermogenesis and therefore energy expenditure.)

Harvard researchers began a (newly published) study with the belief that something besides “just” exercise expends energy.  What they found was a hormone (irisin) that increases as a result of exercise (running, specifically).  Irisin, it turns out, transforms white fat cells into brown fat cells; that is, this hormone turns fat cells from insulators to cells that actually burn calories!

What’s really cool about this is that when injected into mice, irisin changes white fat cells to brown.  What results is:

  • increased energy expenditure
  • improvements in obesity, and
  • better glucose (blood sugar) control (which might help those with diabetes)

To summarize:

  • Exercise increases irisin levels.
  • Increased irisin levels change white fat cells to brown fat cells.
  • Brown fat cells reduce obesity!