Fat chance

Throughout the leaner epochs of human history, when food supplies were unreliable, the species would not have survived without a way to hoard calories for later use. That is, without fat. Once a meal has supplied the body’s immediate energy needs, any unused fuel gets converted into long molecules called triglycerides, which are dispatched to fatty tissue where they wait for a signal that the body needs them.

But in an era of high-calorie smorgasbords and 24/7 convenience, unused energy can just pile on year after year, a major reason why one-third of the U.S. adult population is struggling with obesity. Laws of physics — the ones about conservation of matter and energy — dictate that schemes for burning off all that fat are pretty much limited to two options: Diet to lower the amount of energy consumed, or exercise to increase the amount of energy the body needs...

Other than joining a polar bear club, there’s no obvious way to boost your brown fat activity. In May, in the journal Science, Herzig and his colleagues reported that the enzyme COX-2, which is involved in many body processes, plays a role in turning white fat brown. He and his colleagues described experiments in which they rebooted white fat in mice, turning it brown, after increasing the animals’ exposure to COX-2 and mimicking the physiological changes caused by cold. Even more important, mice with new deposits of brown fat lost weight...