Fat That Burns Calories! It's a Miracle!

Until recently, all body fat got a black mark for metabolism. Fat cells were considered the layabouts among body cells, existing purely to store energy (and help create cottage cheese thighs), with virtually no metabolic function. Then, a few years ago, it was discovered that we have two kinds of fat cells – white and brown – that couldn't be more different. One type actually burns calories.

The white cells live up to their long-held reputation as sluggards. But the brown cells are metabolically active, burning calories day in, day out. Thin people have more brown fat than overweight people, and some people who are obese have virtually no brown fat at all. Recently, scientists have discovered that there is a mechanism by which white cells turn brown.

Calorie-Burning Fat

Brown fat is the fat you can learn to love. In one study, a form of brown fat cells burned 250 calories in a mere three hours to warm subjects who were cold. This may explain why I lost five pounds on a three-week rafting trip on the Grand Canyon despite eating up a storm. The weather was unseasonably chilly and I was cold most of the time. My brown fat must have been burning my white fat to keep my body temperature up to par.

Before you rush to the thermostat to dial your house down to 55, consider this: there's a better way to turn your lazy white fat into active brown fat: exercise. In a study at Dana-Farber Cancer Institute in Boston, white fat cells converted to brown fat cells in mice that exercised. The agent is a hormone called irisin, discovered in the study.

Exercise: Making White Fat Cells Brown

Much more research is needed to understand how this all applies to weight loss. What is definite is that we have yet another reason to exercise, which is already known to ward off thinning bones, prevent cancer and cardiovascular disease and literally keep your cells younger by protecting the telomeres that cap your DNA.

Gym, anyone?