RECENT ADVANCES IN METHODS OF ASSESSING DIETARY AMINO-ACID-REQUIREMENTS FOR ADULT HUMANS

The requirements for the indispensable amino acids have been determine d by a number of different methods. Historically, descriptive or gross measures like growth and nitrogen balance have been used. However, te chnological advancements in recent years have resulted in the use of m ore precise and mechanistic metabolic approaches (i.e., plasma amino a cid concentrations, amino acid oxidation, indicator amino acid oxidati on) to examine requirement. Nevertheless, the current recommendations are still based on nitrogen balance studies. Requirement estimates bas ed on other methodologies, such as plasma amino acid concentrations an d direct amino acid oxidation, suggest that the requirement estimates derived from nitrogen balance experiments are too low. However, these higher estimates have also been criticized on conceptual and methodolo gical grounds, resulting in considerable controversy in the area of in dispensable amino acid requirements. A new technique, indicator amino acid oxidation, addresses many of the criticisms directed toward the a lternative methods and the proposed higher requirement estimates. This paper reviews the current knowledge of amino acid requirements and ma kes recommendations in light of new information that has been provided from recent indicator amino acid oxidation research. It is concluded that the nitrogen balance-based estimates of amino acid requirement ar e too low.