Natto is made from fermented soybeans, a product that demonstrates properties to inhibit the progression of infection at the cellular level.
The natto, a fermented soybean dish often served for breakfast in Japan, originated at the beginning of the last millennium and has just begun to be introduced in Spain. But it may contain an answer to a modern problem, Covid-19, according to a new study based on cell cultures from the Tokyo University of Agriculture and Technology (Japan).
Natto was thought to contribute to a longer and healthier life in Japan (the country with the highest life expectancy on the planet and home to more than a quarter of the world’s population aged 65 and over), but was previously found to be a staple in the diets of those least likely to die of stroke or heart disease.
Now, this study, published in the scientific journal Biochemical and Biophysical Research Communications, has shown that the extract made from natto, viscous and strong smelling, can inhibit the ability of the virus that causes Covid-19 to infect cells.
“Traditionally, the Japanese have assumed that natto is beneficial to their health. In recent years, research studies have revealed scientific evidence for this belief. In this studio, we investigated the antiviral effects of natto on SARS-CoV-2, the virus that causes Covid-19, and bovine herpesvirus 1 (BHV-1), which causes respiratory disease in cattle“, highlights the author of the article, Tetsuya Mizutani.
Natto is made by fermenting soybeans with Bacillus subtilis, a bacterium found on plants and in soil. The researchers prepared two extracts of natto from the food, one with heat and one without. They applied the extracts to sets of laboratory-grown cells from cattle and humans.. One set was infected with SARS-CoV-2, while the other set was infected with BHV-1.
When treated with natto extract made without heat, both SARS-CoV-2 and BHV-1 lost the ability to infect cells. However, neither virus appeared to be affected by the heat-treated natto extract.
“We discovered that what appears to be a protease or proteases – proteins that metabolize other proteins – in the natto extract directly digests the receptor-binding domain of the SARS-CoV-2 spike proteinMizutani notes, noting that the protease appears to break down with heat, losing the ability to digest proteins and leaving the virus to remain infectious.
The spike protein is found on the surface of the virus and binds to a receptor on host cells. With an inactive spike protein, SARS-CoV-2 cannot infect healthy cells. The researchers found a similar effect for BHV-1.
“We also confirm that natto extract has the same digestive effects on receptor-binding domain proteins of mutated strains of SARS-CoV-2, such as the Alpha variant“, emphasizes Mizutani.
Although the results are promising, Mizutani also cautioned that further studies are needed to identify the exact molecular mechanisms involved. He also stressed that the research does not provide any evidence that viral infection is reduced by simply eating natto. Once the components are identified and their functions verified, the researchers plan to advance their work toward clinical studies in animal models.