Does Natto Thin Your Blood? The Scientific Evidence Explained

November 14, 2025 •

4 min read

Since the 1980s, the traditional Japanese food natto has been known for its potent fibrinolytic (clot-dissolving) properties, which directly addresses the question, "Does natto thin your blood?". The answer lies in the powerful enzyme produced during fermentation, nattokinase, and its complex effects on the body's cardiovascular system.

Quick Summary

Natto contains nattokinase, an enzyme that can break down fibrin to thin blood and dissolve clots. It also contains vitamin K2, which promotes clotting. This creates a delicate balance that is important to understand, especially concerning drug interactions.

Key Points

Natto contains nattokinase: The fermented Japanese soybean dish produces a potent enzyme with blood-thinning properties.
Nattokinase dissolves blood clots: The enzyme works by breaking down fibrin, the protein that forms blood clots.
Natto's dual effect requires caution: The whole food contains both clot-dissolving nattokinase and clot-promoting vitamin K2.
Avoid mixing with anticoagulant drugs: Nattokinase and its supplements should not be combined with medications like warfarin without medical supervision due to bleeding risks.
Always consult a doctor: Those with bleeding disorders or on medication, or before surgery, should seek professional medical advice before consuming natto or nattokinase supplements.
Supplements offer higher potency: Purified nattokinase supplements provide a more concentrated blood-thinning effect, as they often have the vitamin K2 removed.

The Science Behind Natto's Blood-Thinning Effect

Natto is a traditional Japanese food made from soybeans fermented with the bacterium Bacillus subtilis. During this fermentation process, a potent enzyme called nattokinase is produced. This enzyme is responsible for the distinctively sticky and stringy texture of natto and, more importantly, its powerful blood-thinning, or fibrinolytic, properties. While natto has been a dietary staple in Japan for centuries, the specific actions of nattokinase have become a topic of significant scientific interest globally, leading to its development as a dietary supplement.

How Nattokinase Affects Blood Clotting

The primary mechanism through which nattokinase works is by degrading fibrin, a protein that forms the mesh-like structure of blood clots. Unlike synthetic anticoagulants, nattokinase has a multi-pronged approach to maintaining healthy blood flow. Its effects include:

Direct Fibrinolysis: Nattokinase directly breaks down fibrin, the main protein that holds blood clots together, helping to dissolve existing clots.
Indirect Fibrinolysis: The enzyme enhances the body's natural clot-dissolving mechanisms. It converts pro-urokinase into urokinase and increases the level of tissue plasminogen activator (t-PA), both of which are crucial for activating plasmin, the body's primary clot-buster.
Inhibition of PAI-1: Nattokinase degrades Plasminogen Activator Inhibitor-1 (PAI-1), a protein that normally suppresses the breakdown of clots. By inhibiting PAI-1, nattokinase helps tip the balance in favor of clot dissolution.
Anti-Platelet Aggregation: In addition to dissolving existing clots, nattokinase has been shown to inhibit platelet aggregation, preventing the initial formation of new clots.

Natto's Dual Nature: Nattokinase vs. Vitamin K2

An interesting and crucial detail about consuming natto is that it contains both nattokinase, which thins the blood, and a high concentration of Vitamin K2 (specifically MK-7), which promotes blood clotting. The fermentation process that produces nattokinase is also responsible for the high levels of Vitamin K2. This creates a complex biological interplay. However, the effect of nattokinase is considered strong enough to provide a net anti-clotting benefit for healthy individuals.

This balance is a major reason why medical supervision is necessary for individuals on anticoagulant medications. For those needing a powerful, concentrated effect without the pro-coagulant action of Vitamin K2, supplements often have the vitamin removed.

Important Considerations for Natto Consumption

Before incorporating natto or nattokinase supplements into your diet, it is vital to understand the potential risks and interactions, especially if you have pre-existing health conditions or are taking medication. Consultation with a healthcare provider is always recommended.

Potential Risks and Interactions

Bleeding Disorders: Individuals with bleeding disorders should be cautious, as the anticoagulant effects of nattokinase could potentially worsen their condition.
Anticoagulant Medications: Combining nattokinase with prescription blood thinners like warfarin, apixaban, or aspirin can be extremely dangerous. Nattokinase's effects can amplify the medication's action, significantly increasing the risk of severe bleeding and bruising. Natto's high Vitamin K2 content can interfere with warfarin's mechanism, and purified nattokinase supplements can pose an independent bleeding risk when combined with other blood thinners.
Surgery: To minimize bleeding complications, it is advised to stop taking nattokinase at least two weeks before any scheduled surgery, including dental procedures.
Pregnancy and Breastfeeding: Due to insufficient research on its safety during pregnancy and breastfeeding, nattokinase should be avoided in these situations.
Allergies: As a soybean product, natto can cause allergic reactions in individuals with a soy allergy.

Natto vs. Nattokinase Supplements: A Comparison

To better understand the options, here is a comparison of consuming natto as a whole food versus taking a nattokinase supplement:


Feature	Natto (Whole Food)	Nattokinase (Supplement)
Composition	Contains nattokinase, Vitamin K2 (MK-7), probiotics, protein, fiber, and other nutrients.	Concentrated, isolated nattokinase enzyme. Often has Vitamin K2 removed.
Effect Profile	Balanced effect, as it contains both blood-thinning nattokinase and clotting-promoting Vitamin K2.	Highly potent, targeted blood-thinning effect due to concentration and Vitamin K2 removal.
Dosage Control	Fibrinolytic units (FU) vary per serving, and cannot be precisely controlled.	Dosage is standardized and controlled, measured in Fibrinolytic Units (FU).
Best For	Generally healthy individuals looking for a natural dietary approach to support cardiovascular wellness.	Individuals seeking targeted, potent support for blood circulation, under medical supervision.
Safety with Warfarin	Not recommended, as Vitamin K2 can interfere with medication.	Not recommended and potentially dangerous; high bleeding risk.

Conclusion

Yes, natto does contain nattokinase, a powerful enzyme that can thin the blood by dissolving fibrin, inhibiting platelet aggregation, and enhancing the body's natural fibrinolytic activity. This makes it a potential dietary aid for supporting cardiovascular health and improving blood circulation. However, the whole food contains a counteracting dose of Vitamin K2, which promotes clotting. This means while regular natto consumption may offer benefits for healthy people, individuals on anticoagulant medication must exercise extreme caution. For those with pre-existing conditions or on medication, isolated nattokinase supplements, which often have K2 removed, can pose a heightened risk of bleeding and should only be taken under strict medical supervision. As with any substance that affects blood clotting, always consult a healthcare professional before making changes to your diet or supplement regimen.

For more detailed information on the mechanism of nattokinase, you can review this article: Nattokinase: An Oral Antithrombotic Agent for the Prevention of Cardiovascular Disease.

Frequently Asked Questions

No, it is generally advised to avoid natto if you are on blood thinners like warfarin. Natto contains high amounts of Vitamin K2, which can counteract the effect of warfarin and increase your risk of clotting. Always consult your doctor before making any dietary changes that could affect your medication.

Natto is the whole food, containing nattokinase, Vitamin K2, and other nutrients. Nattokinase supplements contain a concentrated, isolated form of the enzyme, often with the Vitamin K2 removed to maximize the blood-thinning effect.

Nattokinase thins the blood primarily by breaking down fibrin, the protein responsible for holding blood clots together. It also enhances the body's natural ability to dissolve clots by activating other enzymes.

While generally safe, people with a soy allergy should avoid natto. The primary concern is for those on anticoagulant medications, as consuming natto could be dangerous. Some individuals may also experience digestive issues due to the high fiber and protein content.

No. Due to its potent blood-thinning properties and the risk of interaction with other medications, nattokinase supplements should only be taken under medical supervision. It is also advised to stop taking supplements before any surgery.

The research is mixed on the full effects of heat on nattokinase activity, but it is known that the enzyme is quite stable. However, to preserve its full potency, it's often recommended to add natto to cooked dishes rather than cooking it directly.

Preliminary research and animal studies have suggested that nattokinase may help prevent DVT by inhibiting blood clots. Some human studies also indicate positive effects, but more research is needed, and it should not replace established medical treatments.