Bacterial metabolism of soy may lower dementia risk

A metabolite produced following consumption of dietary soy may decrease a key risk factor for dementia — with the help of the right bacteria.

According to a research team led by the University of Pittsburgh, elderly Japanese men and women who produce equol — a metabolite of dietary soy created by certain types of gut bacteria — display lower levels of white matter lesions within the brain. Their study has been published in the journal Alzheimer’s & Dementia: Translational Research & Clinical Interventions.

“White matter lesions are significant risk factors for cognitive decline, dementia and all-cause mortality,” said lead author Akira Sekikawa, an associate professor at the University of Pittsburgh. “We found 50% more white matter lesions in people who cannot produce equol compared to people who can produce it, which is a surprisingly huge effect.”

To obtain this result, Assoc Prof Sekikawa’s research team measured equol levels within the blood of 91 elderly Japanese participants with normal cognition. Participants were sorted by their equol production status, and then 6–9 years later underwent brain imaging to detect levels of white matter lesions and deposits of amyloid beta, which is the suspected molecular cause of Alzheimer’s disease.

The researchers found that while equol production did not appear to impact levels of amyloid beta deposited within the brain, it was associated with reduced white matter lesion volumes. The team also discovered that high levels of isoflavones — soy nutrients that are metabolised into equol — had no effect on levels of white matter lesions or amyloid beta when equol wasn’t produced.

According to Assoc Prof Sekikawa, the ability to produce equol from soy isoflavones may be the key to unlocking protective health benefits from a soy-rich diet; indeed, his team has previously shown that equol production is associated with a lower risk of heart disease. As heart disease is strongly associated with cognitive decline and dementia, equol production could help protect the ageing brain as well as the heart.

Epidemiological studies in Japan, where soy is regularly consumed, have shown that dietary intake of soy isoflavones has been linked to a lower risk for heart disease and dementia. However, most clinical trials in America have failed to show this. Assoc Prof Sekikawa believes that this discrepancy may be due to the microbiome, as 40–70% of Japanese harbour gut bacteria that can convert dietary isoflavones into equol, compared to only 20–30% of Americans.

Assoc Prof Sekikawa said that equol supplements could one day be combined with existing diet-based prevention strategies that appear to lower the risk of dementia. But while he hopes to evaluate the neuroprotective effects of equol supplements in a future randomised clinical trial, he currently urges caution to anyone who might be tempted to purchase equol supplements to stave off dementia.

“This type of study always catches people’s attention, but we cannot prove that equol protects against dementia until we get a randomised clinical trial with sufficient evidence,” he said.

Image credit: ©stock.adobe.com/au/naito8

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