The subjects were fed enough calories to maintain their original weights. So why did the fattest ones fare so much worse? Study coauthor Judy S. Hannah of the Medlantic Research Institute in Washington, D.C., speculates that the production of cholesterol by their excess body fat may have overridden the benefits of the low-fat diet. If the obese subjects could lose weight, Hannah suspects, they, too, might be able to diet their elevated cholesterols down to healthier levels.