The purpose of this study is to test the effectiveness for weight loss and weight maintenance of four diets differing in macronutrient composition: moderate in fat (40 percent energy) with two different protein levels (15 percent and 25 percent), and low in fat (20 percent energy), also with 15 percent and 25 percent protein levels. The study is only accepting participants in the Boston, Massachusetts or Baton Rouge, Louisiana area. For further enrollment information in Boston or Baton Rouge, see Eligibility Criteria or Design Narrative.