Effects of proteins and their corresponding amino acid mixtures on nitrogen balance and body composition in the growing rat.

The efficiencies of nitrogen utilization from intact proteins (casein, gluten, soybean, egg albumin) were compared to that of the respective synthetic amino acid mixtures. Food intake, growth, NER (nitrogen efficiency ratio), (Nitrogen retained/Nitrogen intake) X 100, BV (biological value), TD (true digestibility), liver weight and body composition were estimated on growing rats. Rats fed amino acid mixtures simulating casein, egg albumin and soybean consumed more food and showed more rapid growth than rats fed the intact proteins. Differences in nitrogen utilization and body composition were occasionally observed between the respective intact protein and amino acid mixtures but were in most cases not significant. It is concluded that nutrition with intact proteins cannot be assumed to be equivalent to nutrition with the corresponding amino acid mixture. However, general differences between the two types of feeding regimens were not obvious since the results were influenced by factors such as the amino acid composition of the protein and the amino acid mixture as well as the methodology used for nutritional evaluation. (Nitrogen retained/Nitrogen intake) X 100 and BV but not NER of an amino acid mixture formulated according to a commercial elementary diet was found to be low compared to casein.