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Not medical advice. The Atlas is not a substitute for a clinician who can examine you.

Natto

Fermented Soybean · B. subtilis + K2

Evidence grade 3 of 5, Mixed. Read how the Atlas grades evidence.

4 human trials, about 60 studies, ~1,500 participants. The written rationale for this grade is still being prepared.

FDA
Food (GRAS)
WADA
Not prohibited

Reference only. Not medical advice.

What can go wrong

Natto is very high in vitamin K2, which opposes warfarin and similar vitamin K antagonist anticoagulants and can lower the INR; it is generally treated as contraindicated for people on warfarin, and any dietary vitamin K change should be directed by the prescribing clinician. Isolated nattokinase supplements carry a separate, opposite concern, a theoretical bleeding risk, and should not be used as a substitute for prescribed anticoagulation; documented case reports include clotting after self-substituting nattokinase for warfarin and a fatal bleed on over-the-counter nattokinase. Soy allergy applies, and severe allergic reactions to natto itself have been reported. The strong aroma and sticky texture limit adherence. Anyone on blood thinners or antiplatelet drugs, pregnant, or managing a bleeding or clotting condition should consult a qualified healthcare provider before regular natto or nattokinase use.

Natto is a traditional Japanese food of whole soybeans fermented with Bacillus subtilis var. natto, and it is a rare three-in-one package: a hardy spore-forming probiotic, the single richest tested dietary source of vitamin K2 as MK-7 (roughly 775 to 1,034 micrograms per 100 grams), and the source of nattokinase, a fibrinolytic enzyme studied for blood-pressure effects. Human RCTs of MK-7 at natto-relevant intake are associated with slower bone-density loss and improved arterial stiffness in postmenopausal women, and a large Japanese cohort associated regular natto intake with lower cardiovascular and stroke mortality. Evidence for isolated nattokinase supplements is thinner, limited to modest blood-pressure signals without clinical-outcome trials. Its strong aroma and sticky, stringy texture are polarizing, and its high vitamin K content is contraindicated with warfarin.

Fermented with B. subtilis natto, and the single richest dietary source of vitamin K2.

What people take it for

These are the reasons people give for taking it. They are not effects it has been shown to have.

  • Spore-forming probiotic (Bacillus subtilis var. natto), a hardy fermentation organism
  • Richest tested dietary source of vitamin K2 as MK-7, relevant to bone and arterial calcium handling
  • Whole-food vitamin K2 delivery, shown to raise serum MK-7 and carboxylated osteocalcin
  • Nattokinase, a fibrinolytic enzyme studied as an adjunct for blood pressure
  • Plant protein and dietary fiber from whole fermented soybeans
  • Traditional Japanese staple, associated in cohort data with lower cardiovascular mortality

What people get wrong

  • Often saidYou can get the same K2 from a multivitamin

    ActuallyNatto provides MK-7, the long-half-life K2 form from natural fermentation, at roughly 775 to 1,034 micrograms per 100 grams, far above most supplements, alongside a live spore probiotic and nattokinase. Tsukamoto 2000 (Journal of Bone and Mineral Metabolism) showed that eating natto itself raises serum MK-7 and carboxylated osteocalcin, a whole-food package no single pill fully replicates.

  • Often saidNattokinase supplements work like a natural blood thinner you can swap for prescription anticoagulants

    ActuallyThis is unsupported and documented as dangerous. Memorial Sloan Kettering records a patient who substituted nattokinase for warfarin after valve surgery and developed clots requiring repeat valve replacement, and a fatal internal bleed in an elderly woman using over-the-counter nattokinase. No trials compare nattokinase to warfarin or direct oral anticoagulants for clinical outcomes. Anticoagulation decisions belong with a qualified clinician.

  • Often saidNatto is fine to eat freely if you take warfarin, since it is just a food

    ActuallyIts high vitamin K2 content directly opposes warfarin and can lower the INR, reducing anticoagulation. Case reports and the Italian and MSK pharmacovigilance literature document this interaction; natto is generally treated as contraindicated for warfarin patients. A prescriber should guide any dietary vitamin K changes.

  • Often saidNatto is a Western superfood discovery

    ActuallyNatto is an East Asian food eaten in Japan for roughly a thousand years, with origins reaching into the Yayoi period. Its bacterium was scientifically isolated by Shin Sawamura at the University of Tokyo in 1905, long before Western interest in K2.

Who profits, and who pushes back

  • Memorial Sloan Kettering Cancer Center, Integrative Medicine

    Pushes backAcademic cancer-center herb-and-supplement reference

    Although nattokinase has been promoted as an alternative anticancer treatment, clinical studies have not been conducted; human studies are limited, and preliminary studies suggest nattokinase may lower blood pressure. It may increase the risk of bleeding when combined with anticoagulant, antiplatelet, or fibrinolytic drugs.

  • Anticoagulation and pharmacovigilance clinicians

    Pushes backWarfarin drug-interaction literature

    Natto is rich in vitamin K and can reduce the effect of warfarin and lower the INR; disturbance of warfarin anticoagulation by natto is documented, so natto is generally treated as contraindicated for patients on warfarin.

  • Nattokinase meta-analysis authors (2023 systematic review)

    Pushes backAuthors of the pooled 6-RCT analysis

    While nattokinase may serve as an effective adjunctive therapy for hypertension, the evidence is limited by small sample sizes, variable dosing, and the possibility of publication bias with fewer than ten trials; relatively low-dose nattokinase may have no significant lipid-lowering effect.

  • Vitamin K2 researchers

    Promotes itAcademic

    Cite natto as the premier dietary K2 (MK-7) source; relevant to bone and cardiovascular health.

  • Japanese dietary tradition

    Promotes itCultural

    Centuries of natto consumption, associated with longevity-region diets.

Where the research comes from

Most of the published research on this comes from one place. 56% of it is from Japan. Findings that no unrelated group has reproduced are weaker than the study count makes them look.

Share of published research by country of origin.
PlaceShare of published research
Japan56%
Asia22%
Other22%

Research published from: Japan, Global.

How we got here

Natto belongs to East Asia, not the West. Soybeans and rice straw, the two ingredients that make it, were both present in Japan by the Yayoi period (roughly 300 BCE to 200 CE), and the accepted origin is accidental: warm cooked soybeans meeting the Bacillus that lives naturally on rice straw, in homes or as altar offerings. Several Japanese origin stories compete. One credits Prince Shotoku in the early 7th century; the most popular ties the discovery to the general Minamoto no Yoshiie during the Zenkunen and Gosannen wars of the 11th century, whose armies supposedly spread it along a so-called Natto Road. The word natto first appears in writing around 1068 in the Shinsaru Gakki, though the sticky thread-pulling form was likely named between the 13th and 16th centuries. During the Edo period, Tokyo vendors sold straw-wrapped packets door to door. Scientific identification came in 1905, when Shin Sawamura at the University of Tokyo isolated the responsible bacterium, later designated Bacillus subtilis var. natto.

  1. 300 BCE-200 CEYayoi-period Japan holds all elements for natto: soybeans, rice straw, the Bacillus on that straw, and warm incubation
  2. c. 754Buddhist priest Ganjin is recorded bringing salt-free fermented soy nuggets to Japan, one strand of natto's origin story
  3. c. 1068The word natto first appears in writing, in the Shinsaru Gakki attributed to Fujiwara no Akihira
  4. 1083General Minamoto no Yoshiie is linked by legend to natto's discovery during the Gosannen War, spreading it along the Natto Road
  5. 1600-1868Edo-period Tokyo vendors sell individual straw-wrapped warazuto natto packets door to door
  6. 1905Shin Sawamura at the University of Tokyo isolates the fermenting bacterium, later named Bacillus subtilis var. natto
  7. 1987Sumi and colleagues describe nattokinase, natto's fibrinolytic enzyme, and its clot-dissolving activity in vitro
  8. 2000Tsukamoto and colleagues show that eating natto raises serum MK-7 and carboxylated osteocalcin in healthy people
  9. 2013-2015Knapen 3-year MK-7 RCTs report slower bone loss and improved arterial stiffness in postmenopausal women
  10. 2017The Takayama Study associates high natto intake with lower cardiovascular and stroke mortality over 16 years

At a glance

Bacterium
B. subtilis var. natto
Richest source of
Vitamin K2 (MK-7)
Also provides
Nattokinase enzyme
Taste
Strong, polarizing

What this entry does not yet cover

What follows is unfinished work on our side, not a finding about Natto. A short entry is not a safe entry.

  • Cost and market. We have not documented what it sells for or who sells it.
  • Supply chain. We have not mapped where it is made.
  • Who uses it. We have not documented the user groups.
  • What could change. No forward-looking summary yet.
  • How it compares. We have not set it against the alternatives.
  • Children and teenagers. We have not checked what is known about younger people.

Sources