What Is Natto?

Most people have never heard of natto — but this sticky, pungent Japanese fermented food has been linked to some of the lowest rates of cardiovascular death ever recorded in a large population study, and it's the only natural food source of nattokinase, the enzyme now sold worldwide as a supplement.

In a 16-year study of nearly 29,000 Japanese adults, those who ate the most natto had a 25% lower risk of dying from cardiovascular disease compared to those who ate the least — an association not found with any other soy food. Understanding what natto actually is, how it's made, and what's in it helps explain why.

Table of Contents

• What Is Natto?
• How Natto Is Made: The Fermentation Process
• Natto's Nutritional Profile: What's Actually in It
• How Nattokinase Was Discovered in Natto
• What the Research Says About Natto and Cardiovascular Health
• Natto vs. a Nattokinase Supplement: A Practical Comparison
• BioAbsorb Nattokinase — When Supplementation Makes Sense
• Frequently Asked Questions
• Conclusion

What Is Natto?

Natto (納豆) is a traditional Japanese food made from soybeans that have been cooked and then fermented using a specific bacterium called Bacillus subtilis var. natto. The result is unlike almost any other food: a soft, sticky mass of beans bound together by long, glistening threads, with a strong ammonia-like aroma and a flavour that is sharp, earthy, and slightly nutty. It divides people firmly into enthusiasts and avoiders.

Natto has been eaten in Japan for well over a thousand years, where it is most commonly served at breakfast alongside steamed rice, a raw egg, soy sauce, and mustard. It is also used in sushi rolls, on toast, and even in ice cream — though that last application remains niche. Outside Japan, natto is available in specialty Asian grocery stores and health food shops worldwide, typically sold refrigerated or frozen in small polystyrene packs.

What makes natto nutritionally unusual is not just what's in the soybeans themselves, but what the fermentation process creates and amplifies. Natto contains nattokinase, soybean isoflavone, γ-polyglutamic acid, vitamin K2, and biogenic amines — a constellation of bioactive compounds that researchers believe explain why its health associations stand apart from other soy foods.

How Natto Is Made: The Fermentation Process

The production of natto is straightforward in method but precise in execution. Soybeans are soaked in water, steamed or cooked, inoculated with Bacillus subtilis natto bacteria, and then incubated for approximately 24 hours. The bacteria multiply rapidly through the beans, producing a range of enzymes and metabolites as they digest the soy proteins. The characteristic sticky threads are γ-polyglutamic acid, a polymer produced by the bacteria as a byproduct of fermentation.

The fermentation process does far more than change the texture and flavour. A detailed comparison of unfermented soybeans and natto found that total free amino acids surged from 151.0 mg/100 g in unfermented soybeans to 427.9 mg/100 g after 24 hours of fermentation, and further to 615.7 mg/100 g after post-ripening — a fourfold increase. Protein is broken down into smaller peptides and free amino acids that are easier for the body to absorb, and nattokinase activity increases continuously throughout the fermentation and post-ripening process.

Fermentation conditions matter significantly for the final product's enzyme potency. Temperature, incubation duration, and the specific bacterial strain all influence how much nattokinase activity ends up in the finished natto. This variability is one of the practical challenges of relying on natto as a consistent source of the enzyme — two packs of natto from different brands or with different expiry dates can deliver meaningfully different levels of fibrinolytic activity.

Natto's Nutritional Profile: What's Actually in It

Natto has a broad nutritional profile that goes well beyond its headline enzyme. A typical 100 g serving contains approximately 59% moisture, 16% protein, and 10% lipid. Most of the fats are polyunsaturated, and natto is a meaningful source of complete protein — particularly notable for a plant food.

Beyond macronutrients, natto is rich in dietary fiber, calcium, vitamin K, potassium, magnesium, iron, zinc, molybdenum, vitamin B2, folic acid, niacin, vitamin B6, pantothenic acid, and biotin. It is, by any measure, a nutritionally dense food. Several of its key bioactive compounds are worth understanding individually:

Nattokinase: The enzyme that gives natto most of its cardiovascular interest. Produced during fermentation and found in the sticky, stringy threads of the food, nattokinase is a serine protease with fibrinolytic properties — it can dissolve fibrin, the protein mesh that forms blood clots.

Vitamin K2 (MK-7): Natto contains approximately 900–1,100 micrograms of vitamin K2 (menaquinone-7) per 100 grams — roughly 124 times the K2 content of unfermented soybeans, and the highest concentration found in any natural food. Vitamin K2 plays a role in directing calcium toward bones and away from arterial walls. Importantly, this high K2 content complicates use of natto for anyone on warfarin or other vitamin K-antagonist anticoagulants.

Isoflavones: Natto's isoflavones appear to protect against breast and prostate cancer, menopausal symptoms, osteoporosis, and heart disease, according to research into soy isoflavone biology. Fermentation changes the form of these isoflavones, potentially improving their bioavailability.

γ-Polyglutamic Acid (γ-PGA): The compound responsible for natto's characteristic stringiness also acts as a prebiotic and has been studied for potential roles in calcium absorption and immune function.

One important note on preparation: nattokinase and B vitamins are sensitive to heat, so natto is best eaten without cooking. Heating natto in a microwave or adding it to hot dishes will degrade its enzyme activity. Most Japanese people eat natto cold or at room temperature, directly from the pack.

How Nattokinase Was Discovered in Natto

The story of nattokinase as a defined compound begins in 1987 at Miyazaki Medical College in Japan, where Dr. Hiroyuki Sumi was researching foods with fibrinolytic properties. According to the landmark paper, Sumi and colleagues demonstrated strong fibrinolytic activity in natto, calculating an average activity of approximately 40 CU (plasmin units) per gram of wet weight. They named the enzyme "nattokinase" and characterised its molecular weight (~20,000 Da) and properties. The paper was published in the journal Experientia and has been cited by virtually every nattokinase study since.

What was notable about Sumi's finding was not just that natto contained a fibrinolytic enzyme, but that this enzyme was heat-stable enough to survive the journey from the food to the bloodstream under the right conditions — and that it appeared to be absorbed orally. Fibrinolytic enzymes are not uncommon in fermented foods; similar compounds exist in Korean chungkook-jang, Chinese douchi, and Indonesian tempeh. But nattokinase had a potency that set it apart, and natto's long history of safe human consumption gave researchers a head start on understanding its tolerability.

The decades following Sumi's discovery saw growing interest in isolating, purifying, and standardising nattokinase for use as a supplement — separating the enzyme from its food matrix (and from the high vitamin K2 content that makes raw natto unsuitable for people on anticoagulants) and delivering it in a controlled dose. Today, nattokinase supplements are manufactured through fermentation technology using Bacillus subtilis, then processed to remove vitamin K2 and standardise enzyme activity in fibrinolytic units (FU).

What the Research Says About Natto and Cardiovascular Health

The most compelling evidence for natto's health effects comes from large population studies in Japan, where natto consumption is common enough to generate statistically meaningful data across quartiles of intake.

The most cited of these is the Takayama Study, a prospective cohort study that followed 13,355 male and 15,724 female Japanese adults aged 35 and older, with cardiovascular deaths tracked over 16 years. The results were striking: the highest quartile of natto intake was associated with a 25% lower risk of CVD mortality (HR 0.75; 95% CI: 0.64, 0.88) and a 33% lower risk of ischemic stroke mortality (HR 0.67; 95% CI: 0.47, 0.95) compared to the lowest intake quartile. Critically, no such association was found for other soy foods — not for total soy protein, soy isoflavones, or non-fermented soy products. This specificity to natto, rather than soy in general, strongly implicated natto's unique fermentation-derived compounds — particularly nattokinase and vitamin K2 — as the active factors. For a deeper look at how these cardiovascular associations translate to supplement research, see nattokinase for heart health.

It is important to read these findings correctly. This is observational epidemiological data, not a randomised controlled trial. It establishes association, not causation — and natto consumers in Japan may differ in other dietary and lifestyle ways from non-consumers. The researchers controlled for known covariates, but residual confounding cannot be ruled out. What the Takayama Study does provide is powerful real-world evidence, at population scale, that regular natto consumption is associated with meaningfully lower cardiovascular mortality in a context where natto is a normal dietary staple.

Complementing the population data, clinical trials using purified nattokinase supplements have examined specific mechanisms. In a clinical study of 1,062 participants with hyperlipidemia or early carotid plaque, nattokinase at 10,800 FU per day for 12 months produced significant reductions in carotid intima-media thickness and plaque size, with improvement rates ranging from 66.5% to 95.4%. The same study found 3,600 FU per day was ineffective — a dose-response finding with practical implications for both food and supplement use.

Natto vs. a Nattokinase Supplement: A Practical Comparison

Understanding the relationship between the food and the supplement requires stepping back from the marketing narratives on both sides. They are related but genuinely different tools, each with advantages the other lacks.

Enzyme dose: A standard 50 g serving of natto contains roughly 1,400–2,000 FU of nattokinase activity. The large clinical trial showing atherosclerosis reduction used 10,800 FU per day — a dose that would require eating 5–8 servings of natto every day. A supplement capsule delivers a standardised, precise dose every time. The Japan NattoKinase Association recommends a minimum of 2,000 FU per daily dose for certified supplements.

Dosing consistency: Nattokinase activity in natto varies with the brand, bacterial strain, fermentation conditions, storage duration, and proximity to the expiry date. Fermentation conditions directly determine enzyme potency, which means food-based dosing is inherently imprecise. Supplements, by contrast, are standardised to a specific FU count per capsule.

Vitamin K2 content: Natto's extraordinarily high vitamin K2 content is a double-edged feature. For most people it is a benefit — supporting bone health and potentially arterial health. But for anyone on warfarin or other vitamin K-antagonist anticoagulants, natto's K2 content makes it unsafe without careful medical supervision. Nattokinase supplements can be manufactured with the vitamin K2 removed, making them accessible to people who cannot safely consume natto.

Whole-food benefits: Natto as a food delivers nattokinase alongside isoflavones, probiotics, complete protein, dietary fiber, and γ-polyglutamic acid. A nattokinase supplement delivers only the isolated enzyme. Whether the additional compounds in natto contribute meaningfully to its observed cardiovascular associations is an open research question — but the Takayama Study's finding that natto outperformed non-fermented soy strongly suggests the fermented matrix matters.

Practicality: Natto has a taste and texture profile that many people outside Japan find challenging. For those who enjoy it or are willing to acquire the taste, eating natto regularly is a reasonable whole-food approach. For those who cannot access natto, dislike the food, or need a precise and controlled enzyme dose without vitamin K2, a supplement is the practical alternative.

BioAbsorb Nattokinase — When Supplementation Makes Sense

For most people reading this outside Japan, regular natto consumption is not a realistic daily habit — and for those on anticoagulant medications, the food's high vitamin K2 content makes it actively unsuitable without medical supervision. That's the practical gap that nattokinase supplements were developed to fill.

BioAbsorb Nattokinase delivers 100 mg of nattokinase per capsule, standardised to 2,000 FU of fibrinolytic activity — the minimum dose recommended by the Japan NattoKinase Association for certified supplements. Each capsule is manufactured using DRcaps delayed-release technology: a veggie capsule designed to protect the enzyme from stomach acid and deliver it intact to the small intestine for absorption. Unlike standard enteric-coated capsules, DRcaps are free of phthalates and plasticizers — a meaningful formulation distinction for an enzyme product.

The supplement is non-GMO, produced in a Canadian GMP-certified facility, and designed to be taken once daily on an empty stomach. Taking nattokinase with food can reduce its fibrinolytic activity, since food may activate the stomach's digestive response before the enzyme reaches the small intestine. The same principle applies to eating natto itself — the enzyme is more active when the stomach isn't simultaneously working on a full meal.

BioAbsorb Nattokinase is available in a 60-capsule or 180-capsule supply. For those interested in exploring whether supplemental nattokinase fits into their cardiovascular health routine, the 180-capsule option provides six months of consistent daily use — a meaningful trial period given that the clinical trials showing the most significant results ran for 12 months.

As with any supplement that has fibrinolytic activity, nattokinase should be discussed with a physician before use by anyone on blood-thinning medications, anticoagulants, or antiplatelet drugs. The interaction risk is real, and the decision to combine nattokinase with pharmaceutical anticoagulants requires medical oversight.

Frequently Asked Questions

Is natto the only food source of nattokinase?

Yes — natto is the only food known to contain meaningful amounts of nattokinase. Similar fibrinolytic enzymes are found in other Asian fermented foods including Korean chungkook-jang, Chinese douchi, and Indonesian tempeh, but these contain different enzymes rather than nattokinase specifically. If you're looking for nattokinase from food rather than supplements, natto is the only direct source.

Does cooking natto destroy the nattokinase?

Yes. Nattokinase is heat-sensitive and loses fibrinolytic activity when exposed to heat above around 50–70°C. Nattokinase and B vitamins are best preserved by eating natto cold or at room temperature, as most Japanese people do. Adding natto to hot rice, soups, or microwaved dishes will significantly reduce its enzyme activity — though the food's other nutrients, including protein and isoflavones, are less affected by moderate heat.

How much natto would I need to eat to match a nattokinase supplement dose?

A standard 50 g pack of natto delivers roughly 1,400–2,000 FU of nattokinase. A typical nattokinase supplement provides 2,000 FU per capsule, which is roughly comparable to one pack. However, the large clinical studies showing the most significant cardiovascular effects used doses of 10,800 FU per day — the equivalent of 5–8 packs of natto daily. Variability in nattokinase content between brands and as natto ages also makes food-based dosing inherently imprecise.

Can people on blood thinners eat natto?

This requires careful medical supervision. Natto's extremely high vitamin K2 content — approximately 900–1,100 mcg per 100 g — directly interferes with the action of warfarin and other vitamin K-antagonist anticoagulants. Eating natto while on warfarin can unpredictably alter your INR and increase clotting risk. Additionally, nattokinase itself has fibrinolytic and blood-thinning properties that compound the interaction risk. Anyone on anticoagulant or antiplatelet medications should discuss natto consumption with their physician before making changes to their diet.

Does natto need to be refrigerated?

Yes. Natto is a live fermented food and should be stored refrigerated or frozen to preserve both food safety and enzyme activity. Nattokinase activity decreases as natto approaches and passes its expiry date, so fresher natto delivers more fibrinolytic activity per serving. Frozen natto retains enzyme activity well and is commonly how it's sold outside Japan, where fresh distribution isn't always available.

Is there evidence that eating natto is better than taking a nattokinase supplement?

The two have different bodies of evidence. The strongest cardiovascular data for natto comes from large epidemiological studies showing reduced CVD and stroke mortality in populations that eat natto regularly — but these studies cannot isolate which component of natto is responsible. Nattokinase supplements have randomised controlled trial data showing specific fibrinolytic and cardiovascular effects at standardised doses. For people who can eat natto regularly, it likely provides benefits beyond isolated nattokinase — but for precise, consistent enzyme dosing without vitamin K2, a supplement is the more controllable approach.

Conclusion

Natto is one of the most nutritionally dense fermented foods on the planet — and the only natural source of nattokinase, the enzyme at the heart of a growing body of cardiovascular research. For those who can access and tolerate it, regular natto consumption offers a whole-food source of the enzyme alongside vitamin K2, isoflavones, complete protein, and probiotics, backed by population data showing associations with meaningfully lower rates of cardiovascular and stroke mortality. For those who cannot — whether due to taste, access, anticoagulant use, or the practical challenge of eating 5–8 packs daily to hit clinical trial doses — a standardised nattokinase supplement bridges that gap. To learn more about how nattokinase works as an enzyme and how to take it effectively, visit the complete nattokinase guide, explore the nattokinase dosage guide, or read the full review of nattokinase for heart health.

Research References

1. A novel fibrinolytic enzyme (nattokinase) in the vegetable cheese Natto; a typical and popular soybean food in the Japanese diet. Sumi H, Hamada H, Tsushima H, Mihara H, Muraki H. Experientia, Vol. 43 (1987). The foundational paper that identified and named nattokinase, characterising its fibrinolytic activity and molecular properties from natto samples.
2. Dietary soy and natto intake and cardiovascular disease mortality in Japanese adults: the Takayama study. Nagata C, et al. American Journal of Clinical Nutrition, Vol. 105 (2017). Prospective cohort of 29,079 Japanese adults followed 16 years; highest natto quartile associated with 25% lower CVD mortality and 33% lower ischemic stroke mortality vs. lowest quartile.
3. Effective management of atherosclerosis progress and hyperlipidemia with nattokinase: A clinical study with 1,062 participants. Frontiers in Cardiovascular Medicine, 2022. Largest nattokinase clinical trial to date; 10,800 FU/day for 12 months significantly reduced carotid plaque with improvement rates of 66.5–95.4%; 3,600 FU/day was ineffective.
4. Nutritional Health Perspective of Natto: A Critical Review. Afzaal M, et al. Biochemistry Research International, 2022. Comprehensive review of natto's production, microbiology, nutritional composition, and therapeutic potential; cited for compositional data and bioactive compound overview.
5. Differences in Nutrition and Sensory Quality Between Cooked Soybeans, Fermented Natto, and Post-Ripening Natto. Foods (MDPI), Vol. 15 (2026). Systematic comparison showing fermentation increases free amino acids from 151.0 mg/100 g to 615.7 mg/100 g post-ripening, with nattokinase activity increasing continuously throughout.
6. Effect of Fermentation Parameters on Natto and Its Thrombolytic Property. Foods (MDPI), Vol. 10 (2021). Examined how fermentation conditions affect nattokinase activity and thrombolytic properties; demonstrated that production parameters directly determine enzyme potency in the finished food.
7. Natto: A medicinal and edible food with health function. Food Science & Nutrition (Wiley), 2023. Review covering natto's full bioactive compound profile including nattokinase, isoflavones, vitamin K2, and γ-polyglutamic acid, and their associated health functions.
8. Nattokinase — Natural Products Database. Drugs.com (NatMed Pro), 2026. Clinical evidence summary; cited for pharmacokinetics data (peak serum concentration at 13.3 ± 2.5 hours after 2,000 FU oral dose) and historical consumption context.
9. Natto Vitamin K: Content, Health Effects and UK Safety Guidance. Bolt Pharmacy, 2026. Cited for vitamin K2 concentration data (900–1,100 mcg MK-7 per 100 g natto, 124× unfermented soybeans) and anticoagulant interaction guidance.

About the Author

David Kimbell is a health writer, digital entrepreneur and former aerospace engineer, based in Ottawa, Canada. He loves translating complex science into clear, actionable guidance for consumers seeking evidence-based solutions.

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Important Disclaimers

Medical Disclaimer: This article provides educational information only and is not intended as medical advice. Always consult with a qualified healthcare provider before starting any new supplement, especially if you have existing health conditions, take medications, or are pregnant or nursing.

FDA/Health Canada Statement: These statements have not been evaluated by the Food and Drug Administration or Health Canada. This product is not intended to diagnose, treat, cure, or prevent any disease.