Mary Pearson

Date of Award


Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

First Advisor

David Katz


The purpose of this study was 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. In this randomized, double-blind, placebo controlled crossover trial, twenty-five subjects (mean age 61 years; BMI 25.46 kg/m2) were recruited from the general population of southwestern Connecticut. Subjects underwent endothelial function testing using high frequency ultrasound at baseline and following 4 weeks of each randomly assigned treatment with intervening 4-week washout periods. Treatment assignment included: soy isoflavone protein (SP, 25gm/day) or soy lecithin (SL, 20gm/day) alone with placebo for the alternative treatment; both active treatments; or double placebo. Main outcome measures were endothelial function, assessed as flow mediated dilation (FMD) of the brachial artery, and serum lipids. Twenty-two women completed the trial. Baseline FMD (pre-treatment FMD) was 8.60 + 7.20. No statistically significant (P > 0.05) difference was seen in FMD between treatment assignments. A trend was suggested, however, with FMD highest after treatment with both soy protein and lecithin (7.50 + 9.85), followed by soy protein and placebo lecithin (5.51 + 10.11), placebo protein and soy lecithin (5.35 + 6.13), and lowest after double placebo (4.53 + 7.84). Soy isoflavone protein and soy lecithin significantly (P < 0.05) increased HDL/LDL relative to baseline value (soy isoflavone protein and soy lecithin, 0.64 ± 0.19; soy isoflavone protein and placebo lecithin, 0.58 ± 0.17; placebo protein and soy lecithin, 0.65 ± 0.18; baseline, 0.49 ± 0.15). In this sample of healthy postmenopausal women, soy isoflavone protein and soy lecithin significantly improved the lipid profile. A favorable influence on endothelial function by soy isoflavone and soy lecithin was suggested but could not be confirmed statistically, possibly due to small sample size, timing of testing, dose, or delivery vehicle. Although soy protein consumption is generally recommended as part of a heart-healthy diet, its favorable effects on cardiovascular disease risk factors such as endothelial function and lipids have not been consistently demonstrated in clinical trials, and further investigation into its effects on specific cardiovascular outcomes is necessary before a substantial cardioprotective role for soy protein can be asserted.


This is an Open Access Thesis.

Open Access

This Article is Open Access