In an attempt to meet better the needs of patients with hypermetabolic stress, amino acid formulas have been modified (MAA). As part of a total parenteral nutrition regimen, MAA have been associated with improvement in parameters of nutrition and survival. The safety and efficacy of these formulas in balanced enteral nutrition was assessed in malnourished patients with moderate to high levels of stress undergoing surgery. The nutritional targets were 5 gm/kg/day glucose, 0.8 gm/kg/day fat, and 0.27 gm/kg/day amino acid nitrogen. In an initial nine studies, the MAA nutrition was safe even in the presence of ileus. A double-blind, randomized, prospective trial was then undertaken in 18 patients in an isocaloric, isonitrogenous design with the nitrogen source as MAA (44% branched-chain amino acids) or standard amino acids (28% branched-chain amino acids). The patients receiving MAA had enhanced nitrogen retention, visceral protein mass, and indices of survival.