Group 1 and 3 participants will aim to lose at least 10% of their body weight and drop to the next lower body mass index (BMI) class level; Group 2 participants will aim to maintain their weight. Group 1 and 3 participants will follow the prescribed diet, which will include traditional healthy food and up to two meal replacement supplements. Initially, the diet will be set to result in an overall loss of 800 to 1000 calories per day. Body weight will be monitored during weekly nutritional education and behavioral sessions. For the first 6 months, Group 1 and 3 participants will attend one individual session and three group sessions per month. During Months 7 through 18, participants will attend group sessions once every two weeks and individual sessions once every 3 months. Throughout the study, participants will record food and beverage intake in daily logs that will be collected monthly.