There will be two visits. At the first visit, a medical history and physical examination will be conducted, and blood and urine tests will be done. The total amount of blood drawn will be 10 tablespoons. This visit will last 3 hours. At the second visit, participants will have an oral glucose tolerance test. To prepare for it, they must be on a special diet for 3 days beforehand and keep a diary of eating, sleeping, and physical activities for those 3 days. A urine sample will be taken at the beginning of the visit. Subjects must then drink a very sweet carbonated cola. A small plastic tube will be placed into an arm vein. Blood will be drawn through this tube eight times over 3 hours. The total amount of blood drawn will be 17 tablespoons.