Amino acid fortification of wheat diets fed at varying levels of energy intake to rats.

The effects on growth and nitrogen utilization of protein quality improvement of white bread fed under varying degrees of adequacy of food energy have been studied. Weanling rats were fed white bread bread plus lysine, and bread plus lysine plus threonine at energy levels ranging from 55% to 100% of ad libitum consumption. Weight gain, protein efficiency ratio (PER), net protein ratio (NPR), and net protein utilization (NPU) were measured and plotted against food consumption. The improvement in growth and nitrogen utilization resulting from amino acid fortification of bread, even when food intake was little more than half ad libitum consumption, was significant. For example, the NPR and NPU values obtained with lysine fortified bread fed at 70% of adlibitum consumption were 1.5 to 2 times those obtained with unfortified bread in spite of the fact that the latter rats consumed 25% more food energy. The implications of these findings for practical problems in human nutrition are discussed.