U.S. researchers have found a way to turn “bad” white fat into “good” brown fat, which can burn off calories and weight, the BBC reports. Scientists did this in rats but say it might be possible in humans, too, which could provide a new way to treat obesity. By modifying the expression of a protein that’s linked to appetite, they not only reduced the animals’ calorie intake and weight, but even changed their fat composition, turning white fat into brown. Brown fat is common in babies, and is used to generate body heat, which expends calories, but as we age this brown fat is mostly replaced by white fat, which accumulates around the waist. Different teams have been looking for a way to turn white fat to brown, and now a team at Johns Hopkins University School of Medicine say they may have done it. In the experiment, they suppressed an appetite-stimulating protein called NPY in the brains of rats. Even when they were still fed a very rich diet, they kept more weight off than rats with normally functioning NPY. In the rats with the altered NPY, they found that some of the white fat was replaced with brown.