Epidemiological research has shown that dairy products aid in weight loss and weight maintenance. Some evidence suggests that this effect is due to the whey component (which contains whey proteins and lactose) of milk. Previous work from our laboratory has demonstrated that chronic administration of whey protein concentrate results in decreased body fat and insulin concentration. Recent research (unpublished) from Castonguay and colleagues (University of Maryland, College Park, MD) has suggested that specific combinations of sucrose, maltose and lactose similarly alter body fat levels in rats. This proposed research will provide data to determine the relative contribution of source of protein (whey vs soy) and carbohydrate (mono- and disaccharides) on the observed effects of dairy products on absorption, substrate oxidation and glucoregulation mechanisms that affect body composition.