The present review addresses data from randomized clinical trials on perioperative nutrition in patients with gastrointestinal cancer. It is important to appreciate that different approaches can be used with regard to timing of administration of nutritional support (preoperative versus postoperative), route of administration (parenteral versus enteral) and composition of the admixtures given (standard versus immune-enriched diets). The rationale underlying these approaches may also vary, and may include correction of nutritional status, attenuation of the acute-phase response through better preservation of gut function, and potentiation of the immune response.