Gastrointestinal surgery and critical illness place tremendous stress on the body, resulting in a series of metabolic changes that may lead to severe malnutrition, which in turn can increase postsurgical complications and morbidity and mortality and prolong the hospital length of stay. In these patients, parenteral nutrition is the most widely used form of nutritional support, but administration of enteral nutrition early in the postoperative period is effective and well tolerated, reducing infectious complications, improving wound healing and reducing length of hospital stay. Calorie-protein requirements do not differ from those in other critically-ill patients and depend on the patient's underlying process and degree of metabolic stress. In patients intolerant to enteral nutrition, especially if the intolerance is due to increased gastric residual volume, prokinetic agents can be used to optimize calorie intake. When proximal sutures are used, tubes allowing early jejunal feeding should be used. Pharmaconutrition is indicated in these patients, who benefit from enteral administration of arginine, omega 3 and RNA, as well as parenteral glutamine supplementation. Parenteral nutrition should be started in patients with absolute contraindication for use of the gastrointestinal tract or as complementary nutrition if adequate energy intake is not achieved through the enteral route.