Isoflavone Soy Protein Supplementation and Atherosclerosis Progression in Healthy Postmenopausal Women: A Randomized Controlled Trial

Background and Purpose—Although epidemiological and experimental studies suggest that dietary intake of soy may be cardioprotective, use of isoflavone soy protein (ISP) supplementation as a primary preventive therapy remains unexplored. We determined whether ISP reduces subclinical atherosclerosis assessed as carotid artery intima-media thickness progression. Methods—In a double-blind, placebo-controlled trial, 350 postmenopausal women 45 to 92 years of age without diabetes and cardiovascular disease were randomized to 2 evenly divided daily doses of 25 g soy protein containing 91 mg aglycon isoflavone equivalents or placebo for 2.7 years. Results—Overall, mean (95% CI) carotid artery intima-media thickness progression rate was 4.77 (3.39–6.16) μm/year in the ISP group and 5.68 (4.30–7.06) μm/year in the placebo group. Although carotid artery intima-media thickness progression was reduced on average by 16% in the ISP group relative to the placebo group, this treatment effect was not statistically signific...