A milk protein hydrolysate which is preferably caseinoglycomacropeptide and/or a whey protein in a bioavailable form is used for the manufacture of a composition for the treatment or prevention of diabetes or syndrome X. The invention also relates to a method of treatment or prevention of diabetes or syndrome X utilizing such compositions, a method for assessing proglucagon gene expression and GLP-1 release by a cell line derived from an adenocarcinoma of human caecum.