The role of nutrition in patient care became a part of mainstream medicine at about the end of the 1960s, with the publication of several papers that showed a benefit of nutritional support in the prevention of complications. At that time, the emphasis was on nutrition given by the parenteral route. Since then, a series of studies that compared parenteral nutrition with enteral nutrition have suggested that the enteral route of feeding causes fewer complications than the parenteral route. A careful review of the data shows that nutritional support can increase the risk of complications when given to well-nourished, obese and hyperglycemic patients. The avoidance of overfeeding and hyperglycemia is, therefore, of paramount importance. In this context, enteral nutrition, for which gastrointestinal tolerance limits overfeeding, can protect the patient.