Hypercholesterolemia and atherosclerosis: effects of dietary protein.

Hypercholesterolemia and atherosclerosis can be produced in rabbits by feeding cholesterol-free, semipurified diets containing proteins derived from animal sources, but these effects have not been observed with similar diets in which the protein is derived from plants. This difference appears to be largely caused by differences in amino acid composition of the dietary proteins. Epidemiologic data on human populations show a strong positive correlation between dietary animal proteins and mortality from cardiovascular disease. It has also been found that the level of plasma cholesterol in human subjects can be reduced significantly by substituting soybean protein for animal protein in the diet. Studies of the mechanism of action of dietary protein have shown that rabbits fed casein have a slower turnover of plasma cholesterol, excrete less neutral steroids and bile acids, and absorb cholesterol from the intestine more readily than rabbits fed soy protein in cholesterol-free, semipurified diets. The excess cholesterol in the plasma of casein-fed rabbits is carried mainly in the very low-density and intermediate-density lipoproteins. These lipoproteins also contain increased amounts of apoproteins corresponding to apo E and apo C, show differences in turnover rates compared to the corresponding lipoproteins from rabbits fed soy protein.