In the April 9, 2009, issue of the New England Journal of Medicine, there was an article discussing the activation of brown fat in humans. There are two types of fat on the body. White fat is primarily a storage site for fat, whereas brown fat is rich in mitochondria (hence the brown color) that can metabolize stored fat to generate heat. In rats, the presence of brown fat is extensive. In humans the levels of brown fat are much less and restricted mainly to the shoulder blade area (which doesn’t contain a lot of excess fat) with virtually no brown fat in the adipose tissue (where virtually all excess fat is located).
In this experiment, the subjects of varying levels of obesity were stuck in a cold room at 60F for about two hours and then assayed for the ability of the fat cells in the shoulder area to burn fat. If you are kept in the cold, the brown fat is activated, but only in the already lean individuals. In the obese individuals, there was very little response. The first thought from this paper is to how make a new drug that will activate the existing brown fat. Of course, maybe the obese individuals genetically don’t have very much brown fat to begin with; therefore, any drug would be worthless for them because there is nothing to activate.
On the other hand, if you are genetically lucky and have larger deposits of brown fat, you are probably thin in the first place. And if you begin to gain weight, just turn down the thermostat. Unfortunately, most people would prefer to be fat and warm in the winter as opposed to thin and miserable.