Want to build up your brown fat, the kind of fat that burns calories rather than stores them? You can exercise, or you can turn down the heat. Up to you. HealthDay reports on research conducted at the National Institutes of Health suggesting that both moderate exercise or shivering from being cold increased people’s levels of the hormones “irisin”(produced by muscle) and “FGF21” (produced by brown fat), both of which turn bad white fat into good brown fat. Yes, it’s a good thing. Shivering, however, was far more efficient: the increase in irisin levels after 10 to 15 minutes of shivering were about the same as after an hour of moderate exercise on a stationary bicycle. Read more in HealthDay.