Abstract: The invention relates to the use of alpha-ketoglutarate or analogues thereof in the preparation of a medicament for treatment of critically ill patients for improving protein synthesis capacity, maintaining energy level, preserving the lean body mass and for improving the glutamine content in skeletal muscle. The medicament contains preferably alpha-ketoglutarate in such an amount, so that it provides more than 0.25 g/kg body weight/day of alpha-ketoglutarate, when administered to the patient. The medicament can also comprise conventional amino acid solution and/or glutamine or analogues thereof, L-asparagine and/or acetoacetate. The invention also relates to a composition comprising conventional amino acid mixture and alpha-ketoglutarate or analogues thereof, in such an amount, so that it provides more than 0.25 g/kg body weight/day of alpha-ketoglutarate, when administered to the patient, optionally with the addition of glutamine or analogues thereof, L-asparagine and/or acetoacetate, glucose and/or fat.