Obesity is a growing epidemic with subsequent health consequences leading not only to reduced quality of life but also to increased medical costs. Growing evidence supports a relationship between increased calcium intakes and reductions in body weight specific to fat mass. Since the first observations in rats >10 y ago, several recently published clinical studies support this relationship as well. The impact of calcium intake on weight loss or prevention of weight gain has been demonstrated in a wide age range of Caucasian and African-Americans of both genders. This review focuses on the results of clinical trials that have investigated the impact of calcium and dairy products on prevention of weight gain, weight loss or development of the insulin resistance syndrome. The implications of these results are that calcium may play a substantial contributing role in reducing the incidence of obesity and prevalence of the insulin resistance syndrome.