The present invention pertains to a) beta-lactoglobulin or b) a nutritional composition comprising beta-lactoglobulin for use in preventing and/or treating a metabolic disorder and/or muscle atrophy. It also pertains to a method of preventing and/or treating a metabolic disorder and/or muscle atrophy in a subject. It furthermore pertains to use of a) beta-lactoglobulin or b) a nutritional composition comprising beta-lactoglobulin for increasing the level of insulin and/or glucagon in the blood of a subject and the present invention also pertains to a non-therapeutic use or method of a) beta-lactoglobulin orb) a nutritional composition comprising BLG. It also pertains to beta-lactoglobulin (BLG) for use in preventing and/or treating diabetes or prediabetes in a subject. It furthermore pertains to a nutritional composition for use in preventing and/or treating diabetes or prediabetes in a subject.