The effect of dietary lysine to arginine ratio on cholesterol kinetics in rabbits.

The effect of varying the compositions of dietary proteins on the relative cholesterolaemic effects of animal and vegetable proteins was investigated in rabbits. In experiments using high fat diets, the amino acid compositions of dietary proteins (soya or casein) were altered by blending them 1:1 (w/w) with gelatin. This reduced the differences in amino acid compositions and also made soya more and casein less hypercholesterolaemic. In experiment 2a, soya protein was compared with dried skim milk in low fat diets and in experiment 2b, these proteins were supplemented with lysine or arginine, respectively, so that the lysine:arginine ratio of soya was similar to dried skim milk and vice-versa. Serum cholesterol was significantly higher in milk-fed than soya-fed rabbits and was not influenced by reversing the lysine:arginine ratio. In the three experiments, parameters of cholesterol kinetics were estimated from the die-away curve of injected [4 14-C]cholesterol. There were no significant effects of diet on the parameters of cholesterol kinetics. It was concluded that the lysine:arginine ratio of the diet is not the major determinant of the cholesterolaemic properties of proteins, but that the overall amino acid composition is primarily concerned.