Specialized enteral and parenteral nutrition are now a standard components of care in critically ill patients. This adjunctive therapy corrects and prevents nutrient deficiencies, attenuates the loss of body protein, and improves clinical outcomes in malnourished patients. Several novel strategies designed to improve the metabolic and clinical effects of specialized nutrition are under vigorous clinical investigation. These new approaches include increased emphasis on enteral feeding to maintain intestinal absorptive, immune, and barrier function; administration of conditionally essential amino acids (glutamine, arginine); use of specialized lipid products and antioxidants; and administration of growth factors such as human growth hormone. Randomized, controlled clinical trials will define the clinical and metabolic efficacy and cost-effectiveness of these therapies in specialized nutrition support.