What is Natto?

Natto is a centuries-old Japanese staple made by fermenting whole soybeans with the bacterium Bacillus subtilis var. natto. The fermentation process transforms ordinary soybeans into a nutrient-dense superfood with a sticky texture and pungent flavor. It is uniquely rich in nattokinase — an enzyme not found in significant amounts in any other food — as well as one of the most bioavailable forms of vitamin K2 known.

How does Natto work?

Nattokinase works by helping the body break down fibrin, the protein that forms blood clots, supporting healthy circulation and reducing the risk of dangerous clots. Vitamin K2 (MK-7) directs calcium away from arteries and into bones, supporting both heart health and bone strength at the same time. The Bacillus subtilis bacteria in natto also acts as a probiotic, supporting gut health and immune balance.

What forms does Natto come in?

Eating whole natto (typically 40–100g per day) provides the full combination of nattokinase, K2, probiotics, and spermidine together. Isolated nattokinase capsules (typically 100–200mg or 2,000–4,000 FU) are used by people who want the cardiovascular enzyme without the K2 — important for those on blood thinners. MK-7 supplements derived from natto are widely available for bone and cardiovascular support. Natto powder is a middle-ground option for adding to smoothies or foods.

Where it comes from:

Natto has been eaten in Japan for over 1,000 years, with historical records dating to the Heian period (794–1185 AD). It was traditionally associated with longevity and consumed by samurai warriors for stamina. Japanese regions with the highest natto consumption have historically shown lower rates of cardiovascular disease and osteoporosis, observations that eventually led researchers to isolate and study nattokinase in the 1980s.

What does Natto help with?

• Heart disease and cardiovascular health: Natto is one of the most studied fermented foods for heart health. Its combination of nattokinase (which keeps blood flowing smoothly) and vitamin K2 (which keeps calcium out of artery walls) makes it a genuinely two-pronged cardiovascular food. Regular natto eaters in Japan have significantly lower rates of heart disease and stroke.
• Blood clots and poor circulation: Nattokinase is a natural clot-dissolving enzyme that helps break down excess fibrin in the blood — the material that forms dangerous clots. Clinical trials have shown it can reduce markers of clotting and improve blood flow, making it useful for people at risk of DVT, stroke, or sluggish circulation.
• High blood pressure: Nattokinase has been shown in human trials to modestly but meaningfully lower both systolic and diastolic blood pressure. Researchers think it works partly by improving blood vessel flexibility and reducing the activity of an enzyme that raises blood pressure (ACE inhibition).
• Osteoporosis and bone loss: The MK-7 form of vitamin K2 in natto is one of the most effective natural nutrients for bone health. It activates proteins that bind calcium into bone matrix rather than letting it accumulate in soft tissue. Clinical trials show MK-7 supplementation reduces bone loss and fracture risk, especially in postmenopausal women.
• Gut health and digestion: Natto is one of the few foods that naturally contains live Bacillus subtilis, a spore-forming probiotic that survives stomach acid well and colonizes the gut more reliably than many other probiotics. Regular natto eating is associated with healthier gut microbiome diversity and improved bowel regularity.
• High cholesterol: Nattokinase and the isoflavones in natto have both shown modest cholesterol-lowering effects in some clinical studies. While natto is not a substitute for medical treatment of severe hypercholesterolemia, it can be a meaningful dietary addition for people managing borderline-high cholesterol through lifestyle.
• Inflammation: Fermented soy contains bioactive peptides and isoflavones that help calm chronic low-grade inflammation — the kind linked to aging, joint pain, and metabolic disease. Natto's fermentation process makes these anti-inflammatory compounds more bioavailable than those in plain soybeans.
• Immune support: Bacillus subtilis strains in natto stimulate gut-associated immune defenses and have shown antiviral and antibacterial properties in research. A healthy gut lining — which natto supports — is one of the most important pillars of a strong immune system.
• Healthy aging and longevity: Natto is one of the richest dietary sources of spermidine, a compound linked to cellular autophagy — the process by which cells clean out damaged components and renew themselves. Higher dietary spermidine intake has been associated with lower all-cause mortality in population studies.

What can Natto help prevent?

• Arterial calcification: MK-7 from natto activates proteins that direct calcium away from artery walls, reducing arterial stiffness over time
• Osteoporotic fractures: long-term MK-7 supplementation has reduced fracture risk in clinical trials of postmenopausal women
• Deep vein thrombosis (DVT): nattokinase supports healthy fibrin breakdown and blood flow, reducing clot formation risk in at-risk individuals
• Stroke: population data from Japan associates regular natto consumption with meaningfully lower stroke mortality

Which foods are rich in Natto?

1. Natto (whole fermented soybeans): The original and only significant whole-food source of nattokinase and high-concentration MK-7. A single 100g serving provides roughly 1,000+ mcg of MK-7 — far more than any other food.
2. Hard aged cheeses (Gouda, Brie, Munster): Among the best non-natto sources of vitamin K2 (MK-7 and MK-4), supporting arterial and bone health. Gouda is particularly rich compared to most other cheeses.
3. Chicken liver and organ meats: A meaningful source of vitamin K2 (mostly MK-4 form) as well as other nutrients that overlap with natto's benefits including PQQ precursors and B vitamins.
4. Tempeh: Another fermented soybean food with probiotic activity and isoflavones, providing some of natto's gut and anti-inflammatory benefits, though it lacks significant nattokinase.
5. Miso: Traditional Japanese fermented soy paste with probiotic cultures and isoflavones. Shares natto's gut-supportive and inflammation-calming properties, though with minimal K2 or nattokinase.

Practical Tips:

Natto is unique because no other commonly eaten food comes close to its nattokinase content. If you cannot eat natto, the closest dietary strategy is to combine fermented dairy (for K2), fermented foods like tempeh or miso (for probiotic isoflavones), and leafy greens (for K1, which the body can partially convert to K2). Supplemental nattokinase and MK-7 are the most practical alternatives for those who dislike natto's strong flavor and texture.

What are the side effects of Natto?

• Digestive discomfort or bloating in people sensitive to fermented or soy-based foods
• Strong smell and sticky texture that some people find unpleasant (not a health risk, but a common barrier)
• Possible soy-related hormonal concerns in people with estrogen-sensitive conditions — evidence is mixed, consult a healthcare provider
• Increased bleeding risk if nattokinase is combined with blood-thinning medications
• Rare allergic reactions in individuals with soy allergy

Good to know:

Natto is extremely safe as a traditional food with a centuries-long history of regular consumption. Most people tolerate it well. The main clinically relevant concern is its interaction with blood-thinning medications due to very high vitamin K2 content.

How much Natto should you take?

• Recommended daily: Whole food: 40–100g of natto per day (1–2 traditional servings). Nattokinase supplement: 100–200mg (2,000–4,000 FU) per day. MK-7 supplement derived from natto: 90–200mcg per day.
• Best time of day: Traditionally eaten at breakfast in Japan. Nattokinase supplements are often taken in the evening since clotting activity tends to be higher at night. MK-7 supplements are best taken with the main meal.
• With or without food: Whole natto is eaten as a meal component, typically over rice. Nattokinase supplements may be taken with or without food. MK-7 should be taken with a fat-containing meal to improve absorption (it is fat-soluble).
• Time to effect: Circulatory and clotting effects of nattokinase: days to 2 weeks. Blood pressure effects: 4–8 weeks of consistent use. Bone density improvements with MK-7: 6–12 months of daily use.
• How long to take it: Natto is safe for lifelong daily consumption as a traditional food. Nattokinase and MK-7 supplements are generally used continuously for chronic conditions like cardiovascular support or bone maintenance — no need to cycle unless directed by a healthcare provider.