Fat is fat, and most of us have too much of it. But even though white fat the kind that that most of are familiar with as cellulite on thighs and love handles around the middle isn't something you'd collect voluntarily, there's another kind of fat, known as brown fat, that might be worth holding on to.
Brown fat, so-called because its darker color comes from high concentrations of mitochondria (the energy engines of cells), burns calories at a higher rate than white fat. Think of it as a biological gym its primary function is to blaze through sugar, the body's fuel, to generate heat. Unfortunately, adult humans don't have much of it not relative to white fat. Newborns start out with high concentrations of brown fat; they need it to regulate body heat, once they come out of the womb. (Rodents, whose high metabolic rate requires such an energy sink, also need it.) As babies grow, however, and become more adept at regulating their own body temperature, they lose most of their brown-fat stores.
But several groups of scientists in the U.S. and Europe have recently found that adults retain a considerable depot of brown fat in the front and back of the neck. And that has researchers excited about the possibility of either genetically manipulating white fat to act more like brown fat to devour extra calories, or somehow activating these dormant brown fat stores to burn energy more effectively. Brown fat is known to be more active when the body is cold, for instance when one team asked volunteers in a study to plunge a foot into a bucket of ice water, the researchers saw a spike in activity in the brown fat regions.
That same team of scientists, who are based in Sweden, then turned to their animal models to the answer the critical question: could activating brown fat help people lose weight? Based on their calculations, the answer is yes; about 50 g of brown fat, which was less than the amount that the scientists documented in the neck area of the five volunteers they studied, could burn about 20% of the calories a person consumed in a day. Lean people, it seems, also tend to have larger brown fat stores than obese individuals, suggesting that the fat may be effectively getting rid of more incoming calories in normal weight people.
The downside, of course, is that the energy appetite of brown fat comes with a price heat and researchers would have to figure out a way to safely exploit the caloric sink without throwing the rest of the body's metabolism out of kilter. If they can find a way to do that, they might have a potent new tool, aside from exercise, that can burn off calories as quickly as they come in.