Baby fat, which keeps infants warm, is also know as brown fat. Until recently, scientists believed that this kind of fat was shed as people matured, so that adults only had white, unhealthy fat. But new research shows that brown fat does exist in adults too—and even just a few ounces of it can burn hundreds of calories a day. Most of it tends to deposit around the front of the neck and chest, and is most common in young women.