Isolated soy protein improves endothelial function in postmenopausal hypercholesterolemic women

Background: Postmenopausia and hypercholesterolemia are related to endothelial dysfunction, a pathogenic event in atherosclerosis. Soy protein reduces plasma cholesterol, but there is scanty information about its effect on endothelial function. Objective: To evaluate the effect of isolated soy protein compared to caseinate on plasma lipoproteins and endothelial function in postmenopausal hypercholesterolemic women. Design: Randomized, double-blind, cross-over trial. Setting: Outpatient clinic of the Catholic University of Chile. Subjects: Eighteen healthy, postmenopausal women with hypercholesterolemia were recruited, included and completed the protocol. Interventions: During the trial, all patients followed a low fat/low cholesterol diet and were randomly assigned to receive isolated soy protein or matching caseinate for 4 weeks, and then the alternative treatment until week 8. At pre-study and at the end of the first and second period, plasma lipoprotein levels and endothelial function (flow-mediated dilatation (FMD) of the brachial artery) were evaluated. Results: Plasma total and low density lipoprotein (LDL)-cholesterol concentration were significantly lower with the low fat/low cholesterol diet compared to pre-study, either with caseinate or soy protein. No significant differences in plasma lipid concentration between caseinate or soy protein interventions were observed. FMD did not change with the caseinate. In contrast, when soy protein was administered, FMD was significantly higher compared to pre-study (9.4 +/- 1.8% vs 5.3 +/- 1.2%; P < 0.05) and compared to caseinate intervention (9.4 +/- 1.8% vs 4.9 +/- 1.5%; P < 0.033). Conclusions: These results suggest that in postmenopausal hypercholesterolemic women, soy protein improves endothelial function, regardless of changes in plasma lipoproteins.