Cereal Chem 54:929 - 948.  |  VIEW ARTICLE
Measuring Protein Quality in Humans: A Review and Proposed Method.

V. R. Young, W. M. Rand, and N. S. Scrimshaw. Copyright 1977 by the American Association of Cereal Chemists, Inc. 

Various aspects of the determination of dietary protein quality in human subjects are reviewed. A brief account is given first of some of the factors that affect organ and whole body protein synthesis and breakdown, in order to provide a metabolic rationale on which to assess the various approaches which have been taken to determine protein quality in man. A short discussion of current knowledge concerning amino acid requirements and of factors that affect them and the requirements for protein is also considered in relation to the nutritional significance of dietary protein quality in subjects at various ages and under differing circumstances. Clinical methods for the evaluation of protein quality are reviewed and an analysis is presented of nitrogen (N) balance data from a series of studies in young adult men receiving graded levels of intake of various test protein sources. The importance of multiple levels of test protein intake for critical estimation of protein quality is stressed. Analysis of the nitrogen balance date indicates that protein quality is estimated more precisely from an evaluation of the intersection of the N balance response curve with the line of N equilibrium as obtained with the test protein and compared with that of a reference protein, such as egg or milk protein. This approach is defined as the Relative Nitrogen Requirement (RNR). The RNRs for a soy protein isolate and whole ground wheat protein were 0.83 and 0.68, respectively, when studied in young adult men.