In order to test the relationship between calcium intake and body weight, we propose to conduct a 2-year, randomized, double-blind, placebo-controlled trial of calcium supplementation (1500 mg/day of supplementary calcium vs. placebo) in adults with a BMI greater than or equal to 25 kg/m(2). We will study the effects of supplemental calcium on body weight, body composition, and obesity-related comorbid conditions, such as insulin sensitivity and lipids. The effects of such supplementation on blood pressure will also be systematically evaluated. A control group of untreated, healthy, adults will also be enrolled for comparisons to study subjects.