Immunonutrition: fact, fantasy, and future.

Immunonutrients are molecular compounds that, while being dietary components, also influence immunologic response mechanisms. Substances such as glutamine, w-3 fatty acids, arginine, and/or ribonucleic acid have been added to standard nutritional support solutions, and the use of these formulations is known as "immunonutrition." A number of randomized, controlled trials have demonstrated that recipients of immunonutrition have better outcomes than control subjects receiving standard nutritional support. However, it is possible that standard parenteral or enteral nutrition is actually harmful. We currently lack data from randomized trials showing the efficacy of immunonutrition compared with no nutritional support. Even if such information were forthcoming, these immunonutrients may simply be acting as pharmacologic agents. Finally, because each of these nutritive agents may either up- or downregulate the immune response, the effects may be disease-state specific.