Equol-ibrium shifts: Gut bacteria's abilty to process soy linked to heart protection

By Will Chu

- Last updated on GMT

Studies estimate that East Asian countries have more than double the proportion of people able to produce equol than Western countries. ©iStock/fotokostic
Studies estimate that East Asian countries have more than double the proportion of people able to produce equol than Western countries. ©iStock/fotokostic

Related tags Soybean

Soy could provide protection against heart disease, says a US-Japanese collaboration that links the food and associated metabolites with gut bacteria activity and heart risk factors.

Certain individuals that are able to produce equol - a substance made by specific gut bacteria types when soy isoflavones are metabolised – were have been found to have lower risk factor levels for heart disease.

This finding bodes well for equol’s purported heart-protecting credentials. It is already available as a nutraceutical agent though an exact mechanism and safe dosage has yet to be determined.

"Scientists have known for some time that isoflavones protect against the build-up of plaque in arteries, known as atherosclerosis, in monkeys, and are associated with lower rates of heart disease in people in Asian countries,"​ said senior author Dr Akira Sekikawa, associate professor of epidemiology at University of Pittsburgh School of Health Sciences.

"We were surprised when a large trial of isoflavones in the U.S. didn't show the beneficial effects among people with atherosclerosis in Western countries. Now, we think we know why."

The popularity of soy in Asian countries has been used to explain the low incidences of cardiovascular disease-related cases amongst the region’s populations.

Foods such as tofu, miso and soymilk are a rich source of dietary isoflavones. Daily intake of this nutrient is 25 to 50 milligrams (mg) in China and Japan, while it is less than 2mg in Western countries.

Favourable associations between isoflavones and incident coronary heart disease (CHD) have been observed​ as in Asian countries as well as evidence that suggest equol may have greater atheroprotective properties than other isoflavones.

These findings are in contrast to isoflavone supplements used in trials conducted in Western countries.

“There is a possibility of interaction of isoflavones with other components of soya in populations consuming traditional soya foods,”​ the study said. “This interaction may lead to more beneficial effects than supplementation of individual soya components in clinical trials.”

Japanese not coy with soy

In line with the higher dietary intake of isoflavones in Japan, more than ten times higher levels of serum isoflavones have been reported in Japan than in Western countries. ©iStock

Dr Sekikawa and his team looked at the diet and lifestyle of 272 Japanese men aged 40 to 49.

Isoflavones and equol levels in their blood were assessed and recorded along with coronary artery calcification (CAC) - a risk factor for heart disease.

Other risk factors such as high blood pressure, cholesterol, smoking and obesity were accounted for.

The team discovered that those, who were able to produce sufficient levels of equol had a 90% lower risk of CAC when compared to those, who could not achieve minimal equol production.

"Our discovery about equol may have applications far beyond heart disease,"​ said Sekikawa. "We know that isoflavones may be associated with protecting against many other medical conditions, including osteoporosis, dementia, menopausal hot flashes, and prostate and breast cancers. Equol may have an even stronger effect on these diseases."

Early equol exposure

For subjects who can produce equol in significant amounts the researchers pointed towards specific actions of the gut bacteria in these individuals.

It may be that exposure of isoflavones in Asian subjects at an early age compared with their Western counterparts could play a role in moulding the gut microbiome and its observed actions.

Similar results to this research were found in another case–control study​ of Chinese adults, where urinary levels of equol but not of isoflavones were significantly and inversely associated with incident CHD in women.

However, negative results have been generally reported in a clinical trial​ that tracked post-menopausal women and the effect of dietary isoflavone on a biomarker of atherosclerosis.

The idea of introducing equol supplements as a preventative or protective measure against heart-related illness was addressed by the study.

It pointed to evidence​suggesting that benefits of isoflavones in breast cancer were noted only in those exposed to isoflavones in childhood/adolescence. No evidence exists for its adoption for CHD.

"I do not recommend that people start taking equol to improve their heart health or for any other reason unless advised by their doctor,"​ said Dr Sekikawa. "Much more study is needed."

Source: British Journal of Nutrition
Published online ahead of print: doi.org/10.1017/S000711451600458X
“Significant inverse association of equol-producer status with coronary artery calcification but not dietary isoflavones in healthy Japanese men.”
Authors: Vasudha Ahuja et al​.

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