Nutritive value of the protein of white and wholemeal bread in relation to the growth of rats

Abstract

The comparative value of the protein of wholemeal bread and white bread, in promoting the growth of young rats of both sexes, has been re-examined. With weanling rats the results confirmed previous observations, made by other workers, that the protein of wholemeal bread promotes a better rate of growth than that of white bread. This difference in the rate of growth was also observed when the diets contained 4% skim milk powder and 10% potato powder. With older rats (starting about 5 to 6 weeks afterweanling) the difference in rate of growth, on the diets containing wholemeal bread com pared with those containing white bread, was not so pronounced with male rats and was insignificant with females. Following these observations the lysine content of the wholemeal and white-bread diets was determined using the analytical technique of Moore & Stein (1951) with an ion-exchange resin. With these data as a basis the lysine content of the white-bread diets was raised to that of the wholemeal diets by the addition of L-lysine. The rate of growth of male weanling rats on the supplemented white-bread diet was then no longer inferior to that observed with the wholemeal diet. In further experiments the lysine content of both the white-bread and wholemeal diets was raised to about 1%, so that lysine was no longer the limiting factor in either. Male weanling rats grew equally well on both these supplemented diets. Once the lysine requirement was satisfied there was no evidence of any other essential amino-acid being a limiting factor in the white-bread diets, compared with the wholemeal. It is concluded, first, that the difference in the nutritive value of the protein of wholemeal bread and that of white bread (as measured by the rate of growth of the weanling rat) is due to the higher lysine content of the wholemeal bread. Secondly, that the weanling rat is extremely sensitive to small changes in the lysine concentration in diets when the content of this essential amino-acid is in the range 0·3 to 0·5%.