Japanese Dietary Staple Helps Retain Memories

Memory loss, cognitive decline, and even Alzheimer's happen when there’s damage to the brain's gray matter.

But deeper parts of the brain, where white matter is located, can also suffer damage that leads to cognitive decline and dementia. Doctors recommend keeping blood pressure, blood sugar, and cholesterol under control to protect white matter, but there's an alternative no orthodox physician seems to be aware of.

It's found in soy foods that are popular in Japan.

Key Takeaways

Certain intestinal bacteria convert soy compounds into equol, which has been associated with healthier brain white matter.

A randomized clinical trial is investigating whether daily equol supplementation can slow changes in the brain and cognitive decline.

Emerging research has linked regular natto consumption with lower odds of mild cognitive impairment, although the association doesn't prove cause and effect.

What Are White Matter Lesions?

White matter lesions (WMLs) are markers of damage to tiny blood vessels caused by chronically reduced blood flow. WMLs can affect up to one in five people once they reach the age of 60, and they’re virtually ubiquitous in those over the age of 90.

Apart from aging, the main predictor of WMLs is high blood pressure, but other risk factors are smoking, diabetes, high cholesterol, carotid artery disease, atrial fibrillation, and heart failure.

If WMLs worsen over time, they increase the risk of stroke and promote a more rapid decline in cognition.

So how does the traditional Japanese favorite, soy, help protect against WMLs?

The Many Memory Benefits of Soy

Diets high in soy have long shown positive effects on cognitive function in studies of Japanese men and women. The secret, researchers say, is isoflavones – soy-derived compounds with estrogenic activity. Soy’s “phytoestrogens” may be a problem, but read on. . .

Now, a research group from the University of Pittsburgh discovered soy isoflavones can also protect against WMLs.

In particular, they were interested in equol, a metabolite produced from the isoflavone daidzein. Equol has the greatest estrogenic and antioxidant activity, and is active in the body for a longer period of time than other isoflavones.

Equol benefits human health in many ways. For example, it helps reduce inflammation, decrease the risk of cardiovascular disease, lower the risk of some types of cancer, support post-menopausal health and bone health, and even reduce wrinkles.

Dramatic Reduction in White Matter Lesions

Unfortunately, the conversion of the isoflavone daidzein to equol takes place in the intestines via the action of certain types of gut microbes. While most Japanese people have them due to a diet high in fermented foods, most Americans don't.

For their study, the Pittsburgh researchers measured blood levels of equol in 91 cognitively healthy Japanese people aged 79 to 85. Then, they scanned the participants’ brains using advanced imaging technology and found WMLs in just over half of them. The lesions were at varying levels of development.

Between six and nine years later, researchers tested the people again and found that the higher their blood equol levels, the greater the reduction in WMLs as shown in brain scans. The participants who produced the most equol had white matter lesion volumes that were more than 50 percent lower than those who produced no equol.

Lead author Dr. Akira Sekikawa described this as "a surprisingly high effect."

In 2025, Dr. Sekikawa and colleagues published the Arterial Stiffness, Cognition, and Equol (ACE) trial.

This is a multicenter, randomized, double-blind, placebo-controlled trial involving 369 adults ages 65 to 85 without dementia. Participants receive either 10 mg of equol daily or placebo for 24 months. Researchers are measuring:

• cognitive function

• progression of brain white-matter lesions

• arterial stiffness

The latest trial record lists primary completion for October 2026 and study completion for January 2027.  We'll keep you posted on the results. 

Meanwhile, what does this mean for you?

Increase Your Isoflavone Intake

The good news is that soy is easy to find in your grocery store. The bad news is that eating soy foods is of no value unless you have the right strains of gut bacteria, which, as I mentioned earlier, most Americans don't.

While up to 70 percent of Japanese people can convert daidzein to equol, only 20 to 30 percent of Americans can.

The reason is that residents of Japan and East Asian countries consume 30 to 50 mg of isoflavones per day in fermented foods. In the U.S. and other Western countries, it's less than three mg.

However, researchers from Japan recently reported that "intestinal bacteria that convert daidzein to equol are present in not only the equol producers but also in the non-producers." They wrote that the ability to produce equol depends on how long someone regularly consumes isoflavones; this will range from weeks for some people to perhaps years in others.

So, it's worth acquiring a taste for healthy fermented soy foods such as tempeh, miso, and natto, with the understanding that the brain benefits will come over time.

What About Taking a Probiotic? 

It's an intriguing idea, but unfortunately producing equol is not as simple as adding a typical probiotic to your diet. Equol production depends on having specific intestinal bacteria capable of converting the soy isoflavone daidzein into equol, and common probiotic strains don't necessarily perform this job. 

Researchers have identified several bacterial species involved in equol production and are investigating whether the microbiome can be manipulated to increase it, but there's currently no well-established probiotic regimen proven to reliably turn a non-producer into an equol producer. 

Eating a diverse, fiber-rich diet and fermented foods is the ticket, but if you don’t find these foods appealing, there’s another solution: you can take equol as a dietary supplement.

Supplementing with Equol

If your gut doesn't naturally produce equol, supplements offer another way to obtain it without relying on your intestinal bacteria to make it from soy. 

In fact, researchers in the ongoing ACE clinical trial are giving older adults 10 mg of equol daily for two years to determine whether supplementation can slow changes in brain white matter, preserve cognitive function and improve arterial health. 

That's particularly intriguing because earlier research found that people who naturally produced higher levels of equol had substantially fewer white matter lesions. But until the trial results are available, it's too early to say that taking an equol supplement will prevent memory loss or dementia. 

Summary

Research suggests that equol, a compound produced by certain gut bacteria after consuming soy, may be linked to healthier brain aging. Older adults who naturally produce equol have been found to have fewer white matter lesions in the brain, and researchers are now testing equol supplementation in a randomized controlled trial. Emerging research on traditional fermented soy foods such as natto also points to a possible connection with cognitive health, although more research is needed to establish cause and effect.

Frequently Asked Questions

What is equol?

Equol is a compound produced when certain intestinal bacteria metabolize daidzein, an isoflavone found in soy foods.

Can everyone produce equol after eating soy?

No. Only people who harbor particular types of gut bacteria can naturally convert soy isoflavones into equol. Equol-producing ability also varies considerably among populations.

What does equol have to do with memory?

Research has found an association between equol production and lower levels of white matter lesions in the brain. These lesions become more common with aging and are associated with cognitive decline and dementia risk.

What is natto?

Natto is a traditional Japanese food made from fermented soybeans. Recent observational research has associated regular natto consumption with lower odds of mild cognitive impairment in older adults.

Has equol been proven to prevent memory loss?

No. Earlier findings are promising but don't establish that equol prevents cognitive decline. Researchers are conducting a randomized controlled trial to determine whether equol supplementation affects cognitive function and brain aging.