[Utilization of proteins as related to protein and fat intake]

Low-protein (5%) and high-protein (40%) diets as well as low-fat (5%) and high-fat (40%) diets were fed to weanling rats in a 14-day experiment, the standard diet containing 10% of protein and 10% of fat. The net protein utilization of casein, the liver protein utilization and the activity of the key enzyme of gluconeogenesis in the liver, phosphoenol pyruvate carboxykinase, were determined. The utilization of proteins by the organism was adversely affected by a high intake of proteins and also of fats. This fact and the observed stimulation of gluconeogenesis testify to the physiological and economical unsuitableness of diets containing excessive amounts of proteins and fats. A low fat intake was less detrimental to the utilization of proteins than a high fat intake; a low intake of proteins seemed to improve the utilization, but other parameters evidenced that it is not sufficient. The application of diets with closely graded contents in wide ranges for various times will yield biochemical indicators being of importance as supplementary factors in the determination of the physiological value of nutrients under different conditions.