The paper describes the carbohydrate, lipidic and nitrogen metabolism of the postoperative period which is subdivided into an early and a late phase. Since the metabolism of caloric substrates in the early postoperative period is a stress metabolism with glucose intolerance and wide protein catabolism, the authors emphasise that an insufficient caloric intake is worse than the fasting state and suggest that alternative caloric sources, such as branched chain amino acids, fatty acids and, even, ketonic bodies, should be used.