Effect of soy isoflavone protein and soy lecithin on endothelial function in healthy postmenopausal women.

OBJECTIVE To assess the effects of soy isoflavone protein concentrate and soy lecithin on endothelial function, measured as flow-mediated dilation (FMD) of the brachial artery in healthy postmenopausal women. DESIGN This was a randomized, double-blind, placebo-controlled crossover trial with 25 participants (mean age, 61 years; body mass index, 25.46 kg/m2). The women underwent endothelial function testing at baseline and after 4 weeks of randomly assigned treatment with intervening 4-week washout periods. Treatment assignments included soy isoflavone protein (25 g/day) and soy lecithin (20 g/day), soy isoflavone protein (25 g/day) and placebo lecithin, placebo protein and soy lecithin (20 g/day), and double placebo. FMD and serum lipid levels were assessed at baseline and the end of each 4-week treatment phase. RESULTS Twenty-two women completed the trial. No statistically significant (P > 0.05) difference was seen in FMD between treatment groups. A trend was suggested with FMD highest after treatment with soy protein plus lecithin (7.50 +/- 9.85), followed by soy protein (5.51 +/- 10.11), soy lecithin (5.35 +/- 6.13), and lowest after placebo (4.53 +/- 7.84). Soy isoflavone protein and soy lecithin significantly increased the high-density lipoprotein/low-density lipoprotein ratio (soy isoflavone protein plus soy lecithin, 0.64 +/- 0.19, P < 0.0001; soy isoflavone protein plus placebo lecithin, 0.58 +/- 0.17, P = 0.0058; placebo protein plus soy lecithin, 0.65 +/- 0.18, P < 0.0001) relative to the baseline value (0.49 +/- 0.15). CONCLUSIONS In this sample of healthy postmenopausal women, soy isoflavone protein and soy lecithin significantly improved the lipid profile. A favorable influence on endothelial function could not be confirmed.