Further Observations on the Improvement of Polished Rice with Protein and Amino Acid Supplements

Abstract

The effects of various supplements of protein and amino acids on growth and on the deposition of liver fat in rats receiving a rice diet have been investigated and the imbalance created when the rice diet was supplemented with sufficient lysine to prevent the accumulation of liver fat has been studied in greater detail. A rice diet supplemented with 6% of various animal proteins supported an excellent rate of growth and maintained liver fat an normal levels. A supplement of several essential amino acids was required to give similar results. In short experiments (2 weeks) the retardation in growth caused by including 0.4% of L-lysine·HCl in the rice diet was prevented by increasing the levels of leucine, isoleucine, valine and histidine. In longer experiments the growth-retarding effect of additional lysine disappeared without the addition of other amino acids to the diet. Supplementation of the rice diet with various combinations of amino acids from which one or more of leucine, isoleucine, valine and histidine had been omitted resulted in a retardation of growth but in all instances in which the diet contained at least 0.4% of additional L-lysine · HCl the fat content of the liver approached a normal value. Even after 7 weeks an accumulation of liver fat occurred unless the rice diet was supplemented with this level of lysine. The sequence in which the amino acids of polished rice became limiting for growth was found to differ markedly from that calculated from amino acid analyses. This stresses the need for investigation of the availability to the animal of the amino acids of intact plant proteins. It is suggested that the most practical way of improving the nutritive value of rice diets is by supplementation with foods containing nutritionally well-balanced proteins.