It is accepted that nutrition support is essential in the treatment of critically ill patients. It is also reasonable to initiate nutrition support therapy as soon as possible. Although malnutrition is most frequently associated with a risk for immune dysfunction, it can affect all organ systems. Thus, ICU patients are in need of immunonutrients supplementation. An additional strategy to maximize the benefits is to consider using products supplemented with specific nutrients that modulate the immune system, improve wound healing, and reduce oxidative stress. The lower incidence of infectious complications may follow in shorter lengths of both intensive care units (ICU) and hospital stays. Many studies have concentrated on nutrients to stimulate the function of cellular immunity in these patients. These nutrients include arginine, glutamine and omega-3 fatty acid which has direct effect on T lymphocytes and macrophage. Enteral formulas designed as immune-enhancing diets (IED) contain supplemental amounts of L-arginine, L-glutamine, nucleotides and the long chain polyunsaturated fatty acids: eicosapentaenoic acid (EPA), docosahexanoic acid (DHA) and arachidonic acid (ARA) in addition to nutrient substrates essential for general nutrition and metabolism. These formulas vary considerably in composition of these four primary substrates. They introduce the immune cell function augmentation, inflammation regulation and infections minimization. Glutamine, a conditional-essential amino acid, an essential energy source, a precursor for protein synthesis and donates nitrogen for the synthesis of purines, pyrimidines, nucleotides, amino sugars, and glutathione antioxidant.

Glutamine also plays an important role in enhancing immune cell function with no elevation in proinflammatory cytokine production. The lower levels of glutamine have been associated with impaired tissue healing, immune dysfunction and increased mortality.

Omega-3 fatty acid (n-3 fatty acid or omega-3 fatty acid) directly affects the function of monocyte by membrane characteristic alteration, prostaglandin E2 (PGE2) synthesis that has the action of macrophage phagocytosis, IL-1 and superoxide synthesis. Moreover, omega-3 fatty acid reduces cellular immune response reaction by compete arachidonic acid resulting in less inflammation.

Arginine is considered a nutrient that enhances the immune response. Studies have shown arginine-supplemented immune formulas in helping decrease protein catabolism, improve nitrogen balance, enhance wound healing and wound strength resulted in less infection and shorter hospitalization days. Arginine has also been shown to support the immune system by enhancing lymphocyte proliferation and phagocytosis. Arginine may provide some benefits. However, recent meta-analysis conducted in a subgroup of critically ill patients by Heyland and colleagues revealed that arginine may be harmful to some group especially septic patients by stimulating nitric oxide (NO) production.

Based on these scientific rationales, it is recommended that arginine should not be used in critically ill patients who are clearly septic. And many evidences exist for supplementation with antioxidant and immunonutrition in the critically ill. Glutamine and fish oil/borage oil should be considered. These result in the development of immune-enhancing diet (IED) without arginine. In addition, two types of lipids are added into the formula to further modulate immune response. First, fish oil as a source of omega-3 fatty acids and borage oil as a source of docosahexanoic acid (DHA), a unique omega-6 fatty acid (n-6 fatty acid). Both n-3 and n-6 fatty acids are polyunsaturated fatty acids (PUFAs) and are essential fatty acids (EFA). Therefore, immune-enhancing diet composes of L-glutamine, eicosapentaenoic acid (EPA), docosahexanoic acid (DHA), antioxidant vitamins and trace minerals such as vitamin A, vitamin E, vitamin C, selenium and betacarotene.