While a plurality of Japanese men experience heart-health benefits from consuming soybeans tofu, soy milk, edamame, tempeh and other soy-based foods the same occurs far less often in American men.

The reason is gut bacteria or microflora.

A University of Pittsburgh Graduate School of Public Health study published recently in the British Journal of Nutrition helps explain how gut bacteria turn an important soy isoflavone into a metabolite known as equol, which in turn is protective against coronary artery calcification.

Soy foods are staples of the Asian diet while Westerners consume minuscule amounts. In general, researchers better understand the biochemistry of how soy foods and other plant foods protect the body from disease. But for many Americans soy is falling short in protecting against coronary heart disease.

The Pitt study, also involving Japanese researchers, found that a clear majority of Asians have intestinal bacteria to metabolize daidzein, a soy isoflavone and plant estrogen, into equol.

Monkey studies clearly demonstrate heart-protective properties of isoflavones, the study says, noting that all monkeys produce equol. In addition, observational studies in Asian countries have documented a significant inverse association between the dietary intake of soy isoflavones and the incidence of coronary heart disease, the study says.

But a recent randomized controlled trial focused on the impact of dietary isoflavones on atherosclerosis in the United States failed to show any benefit, raising the questions about differences in gut biochemistry.

Pitt researchers hypothesized, and ultimately provided evidence, that ones natural ability to generate equol from soy isoflavones was key and involves various forms of gut bacteria.

Individuals able to produce equol, known as equol producers, derive greater clinical benefits from soy foods than individuals referred to as equol nonproducers, the study says. In Asian populations, between 50 percent and 70 percent are equol producers compared with 20 percent to 30 percent of Western populations.

The study shows that equol, rather than the soy isoflavones themselves, generate a protective effect against heart disease for biochemical reasons that now are better understood.

No previous study has examined the association between dietary isoflavones or equol with the presence of coronary artery calcification a well-established biomarker of atherosclerosis independently associated with the risk of coronary heart disease.

Equol producers had significantly lower coronary artery calcification plaque levels in the arteries than those without bacteria that produces equol, it says, calling for clinical trials to confirm the findings.

We need future research from a random clinical trial. But this is a first step, said Akira Sekikawa, an associate professor of epidemiology at Pitt Public Health. It remains unknown, he said, why a higher percentage of Asians are equol producers, including whether higher levels of soy consumption levels are a factor.

The good news, he said, is that dietary supplements containing equol are readily available, typically involving S-equol. Other studies have found equol to be beneficial in reducing menopause symptoms including hot flashes, bolstering bone health and reducing wrinkled skin, with other studies showing potential beneficial effects in preventing Type 2 diabetes, high cholesterol, and breast and prostate cancers.

Equol has a well-recognized effect on arteries, said Kenneth Setchell, a biochemist at the Cincinnati Childrens Hospital Medical Center, and author of The Simple Soybean and Your Health. In recent dietary intervention studies we published using a soy germ-based food (pasta) we observed significantly greater cardio-protective effects in the presence of isoflavones, and the effects were significantly greater in those subjects that were equol producers.

Those benefits, he said, include improvements in the flexibility of arteries.

So the finding of less arterial calcification in this study is important as it would contribute in maintenance of healthy blood vessels and thus an associated lower risk for cardiovascular disease, he said.

David Templeton: dtempleton@post-gazette.com or 412-263-1578.

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Gut bacteria determines the beneficial impacts of soy food on heart health - Pittsburgh Post-Gazette