Type 2 diabetes is more frequent in Japanese Americans than in Japan or the U.S. non-Hispanic white population. This appears to be due to the effects of ''westernization'' to bring out metabolic changes that lead to diabetes. This study will look at whether increased physical activity and dietary changes will reduce or prevent the metabolic changes that lead to type 2 diabetes in Japanese Americans who have impaired glucose tolerance, a condition intermediate between normal glucose tolerance and diabetes.