EVALUATION OF PROTEIN IN FOODS: VI. FURTHER FACTORS INFLUENCING THE PROTEIN EFFICIENCY RATIO OF FOODS

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Abstract
Diets containing two levels of protein (10 and 15%) and two levels of fat (10 and 20%) were tested in all possible combinations in a 4-week rat growth assay. Protein was supplied by casein or a mixture of plant proteins. The protein efficiency ratio (P.E.R.) for casein found with a diet containing 10% protein and 10% fat was slightly greater than that found with a diet containing 15% protein and 20% fat, approximating the levels found in the "average" Canadian diet. The value for plant protein was similar under both conditions. Efficiency of carcass protein synthesis was much greater in animals fed casein than in those fed plant protein. With both sources of protein, the efficiency of carcass protein synthesis was similar with diets containing 10% protein and 10% fat to those with 15% protein and 20% fat.In additional studies, no effect of Chlortetracycline or source of carbohydrate on P.E.R. of casein was observed.It was concluded that P.E.R. determinations carried out on a 10% protein diet furnish a valid estimate of the nutritive value of protein and have several practical advantages.