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Is Soy the Secret to Longer Life in Japan?

Scientists suggest that fermented soy products such as natto or miso might help explain longer life in Japan.
Japanese cooked white rice with Natto on white background

Japanese people have traditionally had one of the longest life expectancies of any developed nation. There are, of course, many possible explanations for longer life in Japan. Regular exercise, strong social cohesion and universally accessible high-quality health care have all been proposed. One study even determined that people drinking green tea several times a week live longer than those who don’t touch it.

Could Diet Contribute to Longer Life in Japan?

Some experts have suggested that diet, beyond green tea, might contribute to Japanese longevity. A study published in the BMJ suggests that fermented soy, a Japanese favorite, is associated with longer life (BMJ, Jan. 29, 2020). The investigators recruited 92,915 volunteers aged 45 to 74. They followed these men and women for nearly 15 years. This was part of the Japan Public Health Centre-based Prospective Study, which includes 11 public health center areas in Japan. During the follow-up time, slightly more than 13,000 of the participants died. Since they had all answered detailed dietary questionnaires, the researchers were able to look for links.

Soy Alone Was Not the Secret:

Just eating soy, such as tofu, was not linked to greater lifespan. However, higher intake of fermented soy products was associated with a lower risk of mortality during the study. The fermented soy products included miso and natto, a fermented soy food with a distinctive smell and texture. In particular, people who consumed the most natto were significantly less likely to die from cardiovascular causes.

The authors were quick to note that such an epidemiologic association cannot prove that fermented soy foods are the reason for longer life in Japan. Nevertheless, if you like miso or natto, there may be unexpected benefits.

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About the Author
Terry Graedon, PhD, is a medical anthropologist and co-host of The People’s Pharmacy radio show, co-author of The People’s Pharmacy syndicated newspaper columns and numerous books, and co-founder of The People’s Pharmacy website. Terry taught in the Duke University School of Nursing and was an adjunct assistant professor in the Department of Anthropology. She is a Fellow of the Society of Applied Anthropology. Terry is one of the country's leading authorities on the science behind folk remedies. .
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  • Katagiri R et al, "Association of soy and fermented soy product intake with total and cause specific mortality: Prospective cohort study." BMJ, Jan. 29, 2020. https://doi.org/10.1136/bmj.m34
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Natto has a very strong taste! I found it more palatable with lemon and tamari. I was eating it for the K vitamins that are helpful for osteoporosis. It was available at an Asian market in my town. That closed, so no more Natto available for me.

Natto is also supposedly helpful against osteoporosis. But after trying it not once, not twice, but three times, and after much research on tricks to make it barely bearable, I believe natto is utterly inedible to people not raised on it. Alas.

And a question about miso: No one has been able to explain to me why it is considered healthful when it is so very high in sodium (which is considered bad for the bones). I don’t get it.

Very informative but if one is on a blood thinner would natto not enhance that effect? How can one incorporate this product into my diet? I have been eat tempeh as part of a plant-based diet and feel so much better on that diet. Thanks for you important public information.

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