Postoperative metabolism is characterized by increased energy demand and nitrogen loss. Whereas autoregulatory mechanisms are able to meet the energy needs by enhanced lipolysis without endogenous problems, nitrogen loss mainly affects functionally and metabolically important proteins. In order to prevent these protein losses during the acute postoperative period, hypocaloric parenteral nutrition is suggested. The concept of hypocaloric nutrition consists of adequate amino acid substitution of 1.2-1.5 g/kg body weight per day and a low-dosed carbohydrate supply not to exceed 150-200 g per day. According to our own experience, this carbohydrate supply is best done with glucose substitutes like polyoles, since these substrates do no greater damage to the endogenous autoregulatory mechanism and give additional support to hepatic gluconeogenesis so that amino acids can be spared. Analyzing a 6-year period of using both hypocaloric and caloric-adequate postoperative parenteral nutrition we believe that hypocaloric nutrition is as beneficial as higher caloric parenteral nutrition, which in its application and monitoring is more expensive and time-consuming.