Leptin, a protein occurring naturally in the blood, appears to regulate how much fat the body carries by speeding up the metabolism and decreasing the appetite when the body has too much fat  Mice that do not naturally produce leptin have more fat than other mice, but lose fat rapidly when they are given leptin injections
Unfortunately, however, leptin cannot be used as a dietary supplement to control fat, since
people with unusually low levels of leptin in their blood tend to have a high percentage of body fat