Our bodies have two kinds of fat: brown and white. In the simplest of terms, the difference is brown fat burns energy, while white fat stockpiles it. We don’t have much brown fat (and yes, it is actually brown in color), just a few ounces around the back, shoulders, and neck. But a recent study shows it consumes calories like a furnace and can boost metabolic rates by 80 percent when we’re exposed to the cold.
Yet other science finds that a newly discovered hormone dubbed “irisin” actually transforms ordinary white fat into a type of brown fat when we exercise. (This may explain the old conundrum of why we burn more calories during exercise than the amount actually required for the activity.) Much work lies ahead to explain exactly how brown fat works, but harnessing its natural power just might make Americans leaner and healthier.