An extract made from nattō has been shown to inhibit the ability of the coronavirus to infect cells.

Nattō is a sticky and strong-smelling traditional Japanese dish made from fermented soybeans. The Japanese have sworn by it for years; it would even contribute to a long and healthy life. But now it appears that the court can also provide a solution for a modern problem: COVID-19.

Nattō

Nattō, a dish that the Japanese like to eat for breakfast, is made by fermenting soybeans with Bacillus subtilis, a bacterium that occurs in plants and in the soil. “Traditionally, the Japanese assume that nattō is good for health,” says researcher Tetsuya Mizutani. As mentioned, it is thought to make a significant contribution to a long and healthy life: Japan is the country with the longest life expectancy and home to more than a quarter of the world’s population aged 65 or older. “Nattō is high in nutrients,” Mizutani tells Scientias.nl. For example, it is rich in iron, calcium, magnesium, proteins, potassium, vitamins B6, B2, E, K2.

Rice served with natt. Image: Hui Wang via Pixabay

But according to the researchers, there is another beneficial power in nattō. In a new study, the team manufactured two extracts of the Japanese dish (heated and unheated) and applied them to sets of lab-grown cells from livestock and humans. One set was infected with SARS-CoV-2, while the other set was infected with BHV-1 (bovine herpesvirus type 1, or cow flu).

Enzymes

The findings are surprising. Because when the unheated extract was used, both the coronavirus and BHV-1 struggled to infect cells. How is that possible? “From our in vitroexperiments show that the proteolytic enzymes in nattō break down the spike protein of SARS-CoV-2,” explains Mizutani. “The surface of the coronavirus contains so-called ‘spikes’: proteins that allow the virus to bind to the ACE2 receptor and enter human cells. Because the spike protein is rendered harmless by nattō, the coronavirus may not be able to enter the cell.” It means that if nattō breaks down the spike proteins, it prevents the virus from attaching to a human cell. And that way an infection can be prevented. The researchers found a similar effect on BHV-1.

Extract made from nattō appears to break down the coronavirus’ spike protein, inhibiting the virus’ ability to infect human cells. Image: Part of Figure is adopted from Biochemical and Biophysical Research Communications Volume 570, September 17, 2021, Pages 21-25. © 2021 The Authors. Published by Elsevier Inc.

The study provides the first evidence that an extract made from nattō could help prevent COVID-19 infection. Because apparently the ability of the coronavirus to infect cells is inhibited by the extract. “Our study highlights the direct antiviral effects of nattō,” says Mizutani. “Few studies have shown that food has such a direct antiviral effect.”

Food

While the results are promising, Mizutani cautions that further studies are needed to uncover the exact molecular mechanisms. In addition, he emphasizes that the study does not provide any evidence of reduced viral infection simply by eating nattō. The research was carried out in the laboratory on cells from cattle and humans. So there’s a possibility that the findings only apply to a clump of cells sitting in a test tube. “We haven’t done any clinical trials at this point,” said Mizutani. Although the researchers hope to change that once the components have been identified and their functions verified. The next step is then to continue the work towards clinical studies in animals.

However, the researchers are hopeful. According to them, natt could possibly play an important role in our fight against corona. “Nattō may even have the ability to reduce the amount of virus particles in patients’ mouths,” Mizutani said. “In addition, nattō could also reduce the spread of COVID-19 from asymptomatically infected individuals.” And so it is an interesting field of research to explore further. “While there are vaccines for COVID-19, we don’t know if they protect against each variant,” continues Mizutani. In addition, it takes time to vaccinate everyone and there are still reports of fully vaccinated people who still get COVID-19 despite that. “So we need to develop treatments for those who do get sick,” Mizutani argues. “And our study may indicate that.”