The objective of this study was to test the hypothesis that calcium supplementation can prevent weight gain in individuals with overweight/obesity. For that purpose, 340 overweight and obese adults randomized to placebo or calcium carbonate (1,500 mg/day) were followed for 2 years. At the end of the study, there were no significant differences in changes in body weight, body mass index or body fat mass between the two groups. Thus, calcium supplementation over 2 years in overweight/obese adults did not alter body weight or fat gain.