Most people think of fat as inert, but in fact fat cells release powerful chemicals. And in obese people, the fat tissue often produces too many bad hormones and too few good ones.

White fat cells store energy and produce hormones that are secreted into the blood. They release adiponectin, which actually helps to fight diabetes, heart disease and other diseases. But in obese people, fat cells tend to shut down the production of adiponectin, which has negative effects on health.

While a white fat cell stores energy, a brown fat cell's job is basically to generate heat. There is increasing evidence that some humans, particularly those who are lean, tend to have more brown fat cells mixed in with their white fat cells in some regions of their body.

If the body could be persuaded to make more brown fat cells, it could help fight the tendency to gain excess weight.