Effects of dietary soy protein on liver catabolism and plasma transport of cholesterol in hypercholesterolemic rats

Sprague-Dawley rats were fed hypercholesterolemic regimens with either soy protein (S) or casein (HC) as the protein source. Lipid, lipoprotein composition as well as lecithin cholesterol acyltransferase activity (LCAT) were measured in plasma. Liver lipid levels and enzyme activities, cholesterol 7α-hydroxylase and acylCoA cholesterol acyltransferase (ACAT), were also determined. Plasma cholesterol levels were significantly reduced with the S as compared with the HC diet, but LCAT activity was not modified. Cholesterol 7α-hydroxylase, which increases in animals fed hypercholesterolemic diets as compared to controls, was unaffected when S was substituted for casein. In contrast, higher cholesterol ester levels and an elevated ACAT activity were observed in the liver of rats on the soybean diet. Substitution of casein with soy protein reduced cholesterol levels in all lipoprotein fractions but no changes were observed in apoproteins.