[Energy requirements for the synthesis of body proteins during growth as determined in model experiments in rats. 2. Studies with dietary casein and wheat gluten used unsupplemented or supplemented with methionine or lysine].

Rats were used in 7 trials each comprising 9 animals (197 total metabolism trials carried out at an environmental temperature of 30 degree). The animals received casein, casein+methionine, wheat gluten, wheat gluten+lysine as protein sources and were investigated for their nitrogen and energy turnover. The rations fed contained between 10% and 27% protein. Supplementation of the natural proteins with synthetic amino acids positively influenced the growth rate and the rate of N retention. The feeding of wheat gluten as sole protein source induced an absolute depression of the food and energy intake. The rates of tetention of protein and fat energy per animal/day showed opposing trends, in dependence upon the protein levels in the rations. It was found in the trials with casein that the proteins yielded 25%, or 18% of the total energy retention if the rats received low protein rations while the percentage of protein energy retention increased to 49-53%, if the rations contained high protein levels. The rats utilized between 67% and 84% of the metabolizable energy for the turnover of body energy. A negative correlation was found between the levels of energy utilization and protein intake. The energy demends for protein retention were calculated (mean of all trials) to be 1.67 kcal of metabolizable energy while those for fat retention amounted to 1.15 kcal. The energy demands for protein retention were not found to be dependent on the type of protein source used. The maintenance requirements of the rats were 102 kcal of metabolizable energy per kg LM0,75.