Natto and health: what studies say about Japan's fermented soybeans, heart health and longevity
Natto, a traditional Japanese food made from fermented soybeans, has been linked in studies to a lower risk of death from cardiovascular disease. Scientists stress these are observational findings and no single food guarantees a long life.
Natto, fermented soybeans eaten in Japan for more than a thousand years, has recently drawn scientific attention because several studies link it to better cardiovascular health and a longer life. The Hungarian outlet “Magyar Mezőgazdaság” reports on the findings. Researchers note, however, that only an association has been shown, not a cause.
What natto is
The food is made from boiled soybeans fermented with the bacterium Bacillus subtilis var. natto. Fermentation changes the taste and texture and creates biologically active compounds. The smell is distinctive and the consistency stringy and slimy, so not everyone likes it. Even so, demand outside Japan is growing: in 2025 the country exported 5,248 tonnes of natto, almost three times as much as in 2017. China and the United States are the largest buyers.
Nutritional content
A portion of about 50 grams contains 8.3 g of protein, 4.8 g of fibre, 50 mg of magnesium and 330 mg of potassium. It is especially rich in vitamin K2, notably the form menaquinone-7 (MK-7). Vitamin K is needed for normal blood clotting, while K2 helps activate proteins involved in bringing calcium into bone tissue. A meta-analysis of six studies suggests regular natto consumption can improve vitamin K status and some bone metabolism markers, but it has not been shown to prevent fractures.
Heart health and mortality
A study in the “American Journal of Clinical Nutrition” analysed data on nearly 30,000 people. Those who ate the most natto were less likely to die of cardiovascular disease than those who ate it least. A 2020 study in “BMJ” with more than 92,000 adults found that regular consumers of fermented soy foods had an overall mortality risk about 10–11% lower.
Limitations
These are observational studies and do not prove that natto causes a longer life. Overall diet, physical activity, genetics, lifestyle and access to healthcare also affect lifespan. A long-running Harvard University study concluded that close relationships with loved ones also play a major role.
