Soybean protein independently lowers plasma cholesterol levels in primary hypercholesterolemia

Abstract

The effects of the isocaloric substitution of soy for animal protein on plasma lipoprotein lipid and apoprotein levels was examined in 12 outpatients with primary hypercholesterolemia and 4 normals. After stabilization on either a standard NIH-Type IIA low-cholesterol diet (Type II patients), or a regular diet (normals) for 6 weeks, the animal and soy protein diets were administered in random sequence (forward studies: animal → soy, reverse studies: soy → animal) for 6 weeks. The nutrient content and composition of the two experimental diets were the same in all respects except for the type of protein. Body weights remained constant, and the results of both forward (n = 6) and reverse (n = 10) studies were similar. The soy and animal protein diets both lowered plasma cholesterol, low density lipoprotein (LDL) cholesterol and apoprotein B levels in the hypercholesterolemic patients significantly below levels achieved on the basal diets. Since the two experimental diets differed only in their protein constituents, the independent effects of soy protein on plasma lipid and apoprotein concentrations could be determined. The isocaloric substitution of soy for animal protein resulted in additional reductions in the plasma concentrations of total cholesterol by −3.5 ± 5% ( P = 0.05), LDL cholesterol by −6.0 ± 7.2% ( P < 0.015), and apoprotein B by ±6.3 ± 9.7% ( P < 0.05) in the hypercholesterolemic patients regardless of the order in which the diets were administered. There were no changes in these lipids or Apo B in the normolipidemic subjects. Plasma levels of very low density and high density lipoprotein lipids and apoproteins A and E were not affected by the diets. Thus, diets containing soy proteins lower plasma LDL cholesterol more effectively in patients with hypercholesterolemia than do diets containing animal proteins.