Feeding Frequency: A Factor in Dietary Protein Utilization.

Summary Urinary excretion of urea N15 and the activities of hepatic urea cycle enzymes were measured in rats eating ad libitum and in those pair-force-fed against them. The force-fed animals excreted more of the dietary N15 as urea and exhibited a greater hepatic arginine synthetase activity than their controls with free access to food. The results suggest that there is a limit to the magnitude of the load of dietary protein that an organism can utilize per unit of time period for protein synthetic purposes. When the limit is exceeded, “excess” nitrogen is excreted in the urine as enzymatic reactions adapt themselves to disposing of the nonutilized nitrogen.