The appearance of intact macronutrients in the small intestine can result in the activation of an intestinal brake; a negative feedback mechanism from different parts of the intestine to the stomach, the small intestine and to the central nervous system. These processes inhibit food processing, appetite sensations and food intake, and furthermore they increase feelings of satiety and satiation. The researchers will investigate the effects of intraduodenal, intrajejunal and intralileal infusion of casein (protein) on ad libitum food intake, satiation and in vivo release of the gut satiety peptides CCK, PYY and GLP-1 and glucose and insulin.