SOY CONSUMPTION AND CHOLESTEROL REDUCTION - REVIEW OF ANIMAL AND HUMAN STUDIES

Animal proteins such as casein are more hypercholesterolemic than soy protein or other plant proteins when fed to rabbits in low-fat, choles terol-free, semipurified diets, A casein-amino acid mixture produces a hypercholesterolemia similar to that of casein. This appears to be ma inly due to lysine and methionine, although other essential amino acid s probably contribute to the effect. Arginine appeared to counteract t he hypercholesterolemic effects of other essential amino acids, Soy pr otein gave a lower level of serum cholesterol in rabbits than did a so y protein-amino acid mixture, suggesting the presence of factors in so y protein that counteract the effects of hypercholesterolemic amino ac ids, Soy protein is also less hypercholesterolemic than casein in othe r animal species, particularly when the diet contains cholesterol, and substitution of soy protein for animal protein in the diet reduces th e concentration of serum cholesterol in humans. This effect is somewha t variable but is generally greater in hypercholesterolemic than in no rmocholesterolemic subjects. The differing effects of dietary proteins on serum cholesterol concentrations in humans and in rabbits are prim arily due to changes in LDL cholesterol, and the hypercholesterolemia produced by dietary casein is associated with down-regulation of hepat ic LDL receptors.