Soy isoflavones heart benefits again under question: Study

By Stephen Daniells

- Last updated on GMT

Related tags: Coronary heart disease, Heart

Questions have again been raised concerning the consumption of soy isoflavones for improved blood flow and heart health, following publication of a joint Anglo-Australian study.

Short-term ingestion of isoflavones, in combination with soy proteins, has neither a negative or positive effect on risk factors for coronary heart disease, according to findings from UK and Australian scientists published in Clinical Science​.

“The present study is the first to describe invasive in vivo coronary vasomotor and blood flow effects of soy-derived isoflavone consumption in humans,”​ wrote lead author Carolyn Webb from Imperial College London.

The researchers state that they observed “no effect of higher dietary intake of phytoestrogens on cardiovascular disease risk”​.

The study appears to lend support to the stance of the American Heart Association (AHA) from 2006. The association stated in the journal Circulation​ that soy had little effect on cholesterol levels, and raised doubts about health claims associated with soy.

Indeed, Dr Frank Sacks, a member of the AHA panel, said in January 2007: "It's really clear that isoflavones don't contribute anything to cardiovascular benefits."

The study, supported The Solae Company, was a randomized, double-blind study involving 71 people with coronary heart disease (CHD) or CHD risk factors. Participants received either an isoflavone-intact soy protein (Supro Soy, Solae) or an isoflavone-free placebo for five days.

At the end of the study period, the researchers report that, while blood levels of the isoflavones did increase in the isoflavone-intact soy protein group, there were no significant differences between the groups in terms of blood flow.

“Our results suggest that consumption of isoflavone-intact soy protein is neither harmful nor beneficial to the coronary circulation of humans with risk factors for, or established, CHD,”​ stated Webb and her co-workers.

Commenting on the results, Priscilla Samuel, Solae's director, nutrition sciences, scientific and regulatory affairs told NutraIngredients-USA.com: "An overwhelming majority of scientific studies support that the consumption of soy protein does have a positive benefit for human heart health. Solae continues to be interested in nutrition and health research on soy, especially in the area of coronary heart disease (CHD)."

Isoflavones are well known phytoestrogens - active substances derived from plants that have a weak estrogen-like action.

In addition to their potential benefits for heart and bone health in post-menopausal women, the compounds also been studied for their role in cancer prevention and slowing down the aging process in peri-menopausal women, and have proved to be a popular alternative to hormone replacement therapy for those wishing to control menopause symptoms without resorting to drugs.

However, as with heart health the role of soy in each of these health areas is catalogued by conflicting results from studies.

Source: Clinical Science​ December 2008, Volume 115, Pages 353-359"Coronary vasomotor and blood flow responses to isoflavone-intact soy protein in subjects with coronary heart disease or risk factors for coronary heart disease"​Authors: C.M. Webb, C.S. Hayward, M.J. Mason, C.D. Ilsley, P. Collins

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