The purpose of this study is to compare the effectiveness of the Medifast 5 & 1 Plan to a food-based, reduced-energy diet plan. The study will be conducted over 52 weeks, including a 26-week weight-loss phase and a 26-week weight-maintenance phase. 120 participants will be enrolled, with 60 randomized to the Medifast 5 & 1 Plan and 60 randomized to food-based, reduced-energy diet plan. Multiple measures will be performed at baseline, 26 weeks, and 52 weeks, including anthropometry, body composition, blood pressure, blood assays, and appetite sensations.