Protein quality, amino acid balance, utilization, and evaluation of diets containing amino acids as therapeutic agents.

Basic concepts of amino acid nutrition are summarized and quantitative amino acid requirements of different age-groups based on current knowledge are presented. The newer concepts of "conditionally indispensable" amino acids and organ-specific requirements for amino acids are discussed. The concepts of nitrogen balance, limiting amino acid, protein utilization, protein efficiency ratio, and amino acid score for determining protein quality are reviewed, and examples of low-, intermediate-, and high-quality proteins are provided. Problems in assessing efficiency of nitrogen utilization when single amino acids or amino acids in combination with balanced diets are used as therapeutic agents are discussed in relation to the potential roles of the branched-chain amino acids, arginine, and glutamine in trauma and as immunostimulators.