The hypothesis that components of milk protein differ in their effects on food intake, metabolic and hormonal responses in rats was investigated through different study designs. Rats were gavaged with the treatments (0.5 g protein in 4mL water/rat), or a water control, 30 min before feeding. Blood glucose, plasma amino acid, insulin, GLP-1, and ghrelin concentrations at 30 min after gavage were measured. The results showed that all preloads suppressed food intake during different feeding periods (P < 0.05). Furthermore, the effects of glycomacropeptide and whey were stronger than casein and complete milk protein. Similarly, glycomacropeptide and whey increased plasma amino acid, GLP-1 and insulin concentrations more than casein and complete milk protein (P < 0.05). Ghrelin concentrations were reduced equally by all treatments (P < 0.05). Blood glucose was not affected. We conclude that milk protein components differ in their abilities to suppress short-term food intake and that these differences might be partially due to their effects on satiety signals.