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Japanese superfood can't combat COVID-19, but may prolong your life

natto over rice with miso soup

“納豆ごはん” (Natto over rice) by Flickr user Masafumi IwaiCC BY-NC 2.0

Check out Global Voices’ special coverage of the global impact of COVID-19.

Amidst the ongoing COVID-19 pandemic, a beloved Japanese food has become even more popular. Like toilet paper, hand sanitizer and medical masks, natto, a sticky, stringy and some say even smelly fermented dish made from soybeans that is believed to boost the immune system has disappeared from supermarket shelves in Japan in March and April. Luckily, however, it's possible for anyone to make natto at home.

Natto, sometimes compared with cheese, is a traditional Japanese dish made by fermenting soybeans with a bacillus subtilis culture, or nattokin. Loved for its rich umami flavor, natto is a popular and inexpensive daily staple in many parts of Japan, and is eaten on over rice or toast, in sushi rolls, in spaghetti, or by itself, mixed with hot karashi mustard and citrus ponzu sauce.

In mid-March, Nexer, a consumer research company in Japan, found that nearly 40 percent of Japanese people they surveyed incorporated special foods into their diet in order to “boost their immune systems” (免疫力を高める). While garlic and ginger were popular foods in the survey, fermented foods such as yogurt and natto topped the list.

Also in March, rumors spread on social media that natto prevents COVID-19. These rumors were sparked mainly because, in prefectures traditionally associated with natto, such as Ibaraki and Iwate, COVID-19 infection rates have been relatively low. As shoppers started hoarding natto, Japan's Consumer Affairs Agency issued a bulletin debunking the idea the food could protect against COVID-19.

By late April, there were still shortages of natto in Japan, and the food began to be identified in the media as just one of a variety of quack COVID-19 “cures” that also included “wood creosote” (正露丸, seirogan), black tea, garlic, and cocaine.

Natto linked to increased longevity in Japan

However, while natto will definitely not help protect against COVID-19, the fermented “superfood” may actually be connected with increased longevity, according to two recent studies in Japan. In one study, which tracked eating habits and health outcomes of nearly 29,000 people in the city of Takayama between 1992 and 2008, participants who consumed one package of natto at least once a week had a 25 percent lower risk of dying from cardiovascular disease than those who reported rarely eating it.

natto strings

Sticky, stringy natto, ready to be served. Photo by Nevin Thompson.

Another study of about 90,000 middle-aged and elderly people over 15 years conducted by Japan's National Cancer Center found that intake of fermented soy foods, especially natto, was correlated with — if not directly linked to — a lower risk of death from cardiovascular disease and cancer.

While the connection between natto consumption and increased longevity has not been proven, one theory is that nattokinase, an enzyme found in the sticky strands of nattohas been shown to dissolve blood clots and in turn potentially help mitigate heart disease.

‘Fermentation brings intoxication, joy, and freedom’

Despite its irresistible umami flavor or reputation as a superfood, some people are put off by natto's distinctive nutty aroma and sticky texture. Natto is generally more popular in Tokyo and other parts of eastern Japan compared to the rest of the country.

natto starter

Taking a shortcut in the fermentation process and using packaged natto as a starter when making natto at home. Photo by Nevin Thompson.

I wasn’t keen on natto either, in the beginning,” says journalist, author and photographer John Ashburne, in an interview with Global Voices. “It was when Sasha (a chef and Ashburne's wife) prepared it with a raw quails egg and sliced scallions – both of which served to lessen somewhat the pong – that I began to appreciate it.”

Ashburne, a longtime resident of Kyoto and a self-described mushroom cultivator and forager, is a well-known writer on Japanese food who has written a Lonely Planet guidebook on the subject.

Ashburne also makes his own natto at home.

“Fermentation brings intoxication, joy, and freedom. You can escape the tyranny of the food industry by making your own natto,” says Ashburne. “There’s a sense of creating something special, individual and something almost impossible to replicate exactly twice. Even if I wanted it to be, I don’t think my natto would be exactly the same every time.”

Ashburne says he likes to vary the beans he uses, and his process, sometimes steaming the beans, sometimes boiling them, or sometimes preparing over a slow heat with konbu, often without.

“It’s as if the micro-organisms have a mischievous quality, with microscopic minds of their own. Fermentation on a non-industrial scale strikes me more like alchemy than cookery,” says Ashburne.

How to make natto at home

Outside of Japan and other countries where natto is also popular, it can be hard to find it in supermarkets. However, with the right ingredients and cooking equipment, natto can be made at home.

Using one low-temperature method, natto can be made in the oven using sterilized glass jars or even plastic containers. The easiest method for making natto is by using an Instant Pot or pressure cooker. A key challenge will be finding natto starter spores, which contain the nattokin necessary for fermentation. One shortcut is to use packaged natto as a starter for a larger batch.

6 comments

  • Max

    Greetings from Japan!
    Thanks for this article that hopefully introduces many folks to the benefits of fermented foods, particularly, in this case, natto!
    Had to laugh, though, at your reasoning with the statement, “While the connection between natto consumption and increased longevity has not been proven, one theory is that nattokinase, an enzyme found in the sticky strands of natto, has been shown to dissolve blood clots….”! Yes, blood clots consisting of fibrin made substantially of misguided calcium, which also builds up as plaque lining Arterial walls. Nattokinase not only breaks down the fibrin, but also targets calcium moving in body and guides it to where it’s needed and beneficial for the body!
    Check it out….…
    A click/search on “nattokinase” will open up a small world of double~blind, peer reviewed scientific studies establishing that nattokinase, an enzyme of Vitamin K2~M7, of which natto has the highest content of all foods (free range/organically fed chicken eggs taking a far behind 2nd place)! In fact, one serving natto, 30~40 gr.) provides way more nattokinase than the usual dosages used in most of the scientific studies!
    Plus, the probiotics in natto & other fermented foods like sauerkraut, pickles, free range and unpasteurized plain Greek yoghurt have been shown to bolster our bodies’ immune systems, which could make a little or maybe big difference when in the range of COVID-19!!
    Indeed, the Creator of the universe(s) put really all we need in nature, while, sadly, most of us are deceived into or choose to participate in its destruction!!!
    Praying many many more of us wake up and open up our heart to receive MORE Love!!! Meanwhile, take care!

    • Thanks. I’m not a scientist or science reporter, so it’s important for me to be conservative in how I report on science topics in order to prevent the spread of disinformation. I am glad you liked the article!

  • Alberto

    Dear Nevin

    In the last week of April it was noticed that that COVID-19 is linked to higher stroke risk, caused by blood clots released in consequence of the virus action.

    Considering that Natto has been shown (and proved) to dissolve (and prevent) blood clots, Natto should be considered a powerful tool against the COVID-19.

    The Japanese are right to run for Natto. I suggest that you rethink your headline, based on those recent findings.

    • Hi Alberto, thanks for reading the article and taking the time to comment. I did think about this article, and the title, a considerable bit. For reasons explained in a previous comment (see above) we will not consider rewriting the headline at this time. Thanks once again, and stay safe.

  • Rob

    With interest, I read your article about Natto consumption and Covid-19. I was really surprised that you were so convinced that Natto cannot reduce Covid-19 disease severity, without presenting any data to discard the option that it might have been increased relatively high Natto intake in prefecture Iwate that protected that reduced severity of the outbreak Covid-19.

    A study been prepublished that found an inverse correlation between vitamin K status (Natto has high concentrations of very bioavailable vitamin K2) and disease severity (https://www.preprints.org/manuscript/202004.0457/v2 ). These data perfectly fit into the concept that eating Natto may reduce Covid-19 disease severity.

    • Thanks for reading the article. As mentioned above, I’m not a nutritionist, or a health researcher, or a doctor. As a reporter, I do know that there is still no scientific consensus about many, many aspects of COVID-19. It would be irresponsible of me to prescribe an foods as a way decrease severity of the disease.

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