Nutrition and infection.

It is now apparent that nutritional status has a profound impact on immune function and that the immune system may be modulated by the use of specific modes of nutritional support. In selected malnourished or severely injured patients, early nutritional support has been shown to improve outcome and decrease the incidence of infectious complications following major surgery or trauma. Enteral feedings appear to support the immune system better than parenteral feedings. TPN, although a potentially life-saving modality, should not be used indiscriminantly and should be limited to those severely malnourished or injured patients who are incapable of tolerating enteral feedings. The patient's metabolic needs should be assessed as accurately as possible, and the appropriate combination of substrates should be provided according to the patient's level of hypermetabolism. Overfeeding should be avoided. A number of nutritional substrates have been identified which may potentially modulate specific aspects of immune function. Among these, glutamine, arginine, and omega-3 fatty acids have demonstrated potential clinical usefulness. Iron deficiency appears to be a normal host defense response to infection or trauma and should not be compromised by attempts at iron replacement therapy. In summary, optimal nutritional support of the surgical patient supports the immune system and reduces the morbidity and mortality associated with severe malnutrition or injury.