A daily 40 gram dose of soy protein was associated with significant reductions in E-selectin and leptin, whereas no such reductions were observed in people taking the same dose of milk protein, according to findings published in the European Journal of Clinical Nutrition.
The study, led by scientists from the Tulane University School of Public Health and Tropical Medicine in New Orleans, is said to be one of the largest randomized trials to investigate the effect of protein supplementation on multiple biomarkers of inflammation, endothelial dysfunction (the lining of the blood vessels), and adipocytokines (signaling molecules produced by fat tissue).
It is also one of the most generalizable since the study participants were men, women, Caucasians and African-Americans, they added.
“This study provides moderate support for the role of soy protein as a healthy food for cardiovascular health through E-selectin and leptin reduction, which adds to the existing evidence for the cholesterol and blood pressure reducing effects of soy protein,” they wrote.
Soy protein and heart health
The cardiovascular potential of soy protein has been reported many times, and the American Heart Association currently recommends consumption of at least 25 grams per day of soy protein with phytoestrogens, along with a low-fat diet, to reduce the risk of heart disease.
While some studies have examined the effects of soy proteins on the various inflammatory markers, “the existing evidence is limited and inconsistent”, said the researchers.
To help fill these knowledge gaps, 102 men and women were randomized to eight week consumption phases of soy protein (40 grams per day with 89.3 milligrams of isoflavones), milk protein (40 grams per day), or complex carbohydrate (40 grams per day as placebo). Solae/DuPont provided the supplements.
The double-blind, three-phase crossover trial found that there were no significant changes in a host of inflammatory markers, including C-reactive protein, interleukin-6, and tumor necrosis factor-alpha.
However, significant reductions were observed in E-selectin, a marker of endothelial dysfunction, compared with milk protein, and leptin, an adipocytokine, compared with the carb placebo.
“These study findings add to our understanding of the effects of soy protein, especially considering the paucity of rigorously designed and conducted soy protein clinical trials on novel CVD risk factors,” they concluded.
Source: European Journal of Clinical Nutrition
January 2013, Volume 67, Pages 58-63, doi:10.1038/ejcn.2012.186
“Effect of soybean protein on novel cardiovascular disease risk factors: a randomized controlled trial”
Authors: C.M. Rebholz, K. Reynolds, M.R. Wofford, J. Chen, T.N. Kelly, H. Mei, P.K. Whelton, J. He