AIM: To compare the effects of whey versus whey without glycomacropeptide (GMP) in a high and a normal amount of protein in a breakfast custard on satiety and energy intake (EI), taking concentrations of amino acids (AA), glucose, insulin, glucagon-like peptide 1 (GLP-1) and ghrelin into account. METHODS: Twenty-five healthy subjects (mean+/-S.E.M., BMI: 23.9+/-0.3kg/m(2); age: 22+/-1 years) received a breakfast containing whey or whey without GMP as protein type with 10/55/35 or 25/55/20 En% protein/carbohydrate/fat in a randomized, single-blind design. Appetite profile (Visual Analogue Scale, VAS), glucose, insulin, GLP-1, ghrelin and AA concentrations were measured, and the adequate moment for ad libitum lunch was determined based on differences in ghrelin concentration. In a second set of experiments subjects received the same breakfasts; ad libitum lunch was offered at the pre-determined moment. RESULTS: After a breakfast with 25 En% protein increases in insulin and GLP-1 and decreases in ghrelin concentrations were larger; increases in satiety ratings were lower than after 10 En% (p<0.05); there was a treatmentxtime interaction effect on glucose and insulin concentrations (p<0.001). After a breakfast with whey without GMP insulin concentrations were increased more than after whey (p<0.05). EI at lunch was lower after whey than after whey without GMP (2877+/-165kJ versus 3208+/-178kJ, p<0.05), coinciding with more increased concentrations of serine, threonine, alanine, alpha-aminobutyric acid and isoleucine (p<0.05). CONCLUSION: GMP as a whey-fraction reduced energy intake coinciding with increased concentrations of certain amino acids, irrespective of the concentration of whey-protein. Although between different concentrations of whey-protein differences in hormone responses were observed, these were unrelated to satiety ratings or energy intake.