Relation between protein efficiency and net protein utilization

Abstract

The simplest and most convenient method of measuring the nutritive value of proteins is by an assessment of the protein efficiency ratio (P.E.R.) (gain in weight in g/g protein eaten). This measurement has been frequently criticized and, in fact, Mitchell (1924) stated that simplicity was its only recommendation. There are two main drawbacks to the method. Firstly, P.E.R., as measured on any particular protein, increases with the quantity of protein consumed A certain amount of protein is required for maintenance of body-weight, and only the increment above this amount is available for growth. Consequently, when larger quantities are consumed more is available for growth and a higher P.E.R. results. Secondly, the method is based on the assumption that the increase in body-weight on the protein-containing diet is proportional to the protein retained. It has been repeatedly shown that the composition of the weight increase varies with the type of diet during the 6-8 weeks of the usual experiments (Mitchell & Carman, 1926; Hamilton, 1939; Kik, 1938).