Protein Utilization in Growing Rats

Abstract

The application of standard bioassay procedures for the evaluation of the nutritive value of proteins with growing rats has been examined. The slope-ratio technique using gain as the response and nitrogen intake as the measure of dose appears to be most satisfactory. The “relative growth index” is proposed as a satisfactory measure of nutritive value, this being the slope of the regression between dose and response expressed as a percentage of the slope obtained with a protein of maximal nutritive value. It seems apparent that biological value of rather poor quality proteins recorded in the literature overestimates the nutritive value of proteins for growing rats. The biological value of wheat gluten, for example, is recorded as 40, whereas it appears to have a relative growth index of only 20. Since estimates of protein requirements involve the use of biological values, current estimates may be too low. The need for accurate and appropriate estimates of the nutritive value of proteins is stressed. The inadequacies of protein efficiency ratio and its variants as a bioassay are emphasized.