What happens if I eat natto every day?

One tablespoon of natto delivers more vitamin K2 than most people get in an entire day.

So what happens if you eat natto every day? For most healthy adults, one serving supplies close to 998 micrograms of vitamin K2 (MK-7) per 100 grams — the highest of any food — plus a clot-dissolving enzyme and gut-friendly bacteria, and a few trade-offs that matter, one of which is a genuine medical warning.

Table of Contents

• What Natto Is and What a Daily Serving Delivers
• The Vitamin K2 Story: Bone Support and the Warfarin Catch
• Heart and Circulation: What Daily Natto Is Linked To
• Gut Health, Protein, and Everyday Nutrition
• The Real Downsides of Eating Natto Every Day
• Getting the Enzyme Without the Daily-Natto Trade-Offs
• Frequently Asked Questions
• The Bottom Line

What Natto Is and What a Daily Serving Delivers

Natto is a traditional Japanese food made by fermenting whole soybeans with the bacterium Bacillus subtilis over about 24 hours, which creates its signature sticky strands and pungent smell. A 100-gram serving — roughly one small container — supplies around 17.7 grams of complete plant protein, 5.4 grams of fiber, and 212 calories, plus about 48% of the daily value for iron.

What separates natto from tofu or tempeh is the fermentation, not the soybean. The process generates three active compounds at once: vitamin K2 as menaquinone-7 (MK-7), the fibrinolytic enzyme nattokinase, and live Bacillus subtilis cultures. Natto is the richest known dietary source of MK-7 at roughly 998 micrograms per 100 grams.

Eaten every day, those three components drive both natto's reputation and its cautions. A typical Japanese portion is modest — often just 40 to 50 grams, about half a container — yet even that delivers several hundred micrograms of vitamin K2, well above the roughly 90 micrograms an adult needs daily. That concentration is the thread running through everything below.

The Vitamin K2 Story: Bone Support and the Warfarin Catch

Vitamin K2 has a specific job: it activates osteocalcin, the protein that binds calcium into bone, and matrix Gla protein, which helps keep calcium out of your arteries. Because natto floods the body with MK-7 — one tablespoon provides roughly 150 micrograms, above the 90-to-120-microgram daily target — daily eaters sustain unusually high K2 levels, aided by MK-7's long half-life of about 72 hours.

The bone evidence is real but modest. A three-year randomized trial of 244 postmenopausal women taking 180 micrograms of MK-7 daily showed significantly slower bone-density loss and a more than 50% drop in the inactive form of osteocalcin — direct evidence the vitamin was doing its job in bone.

Here is the catch that turns a benefit into a warning. That same vitamin K load directly opposes warfarin, a blood thinner that works by blocking vitamin K. The clinical literature is blunt: natto must be avoided by patients taking warfarin, because its MK-7 — with that 72-hour half-life — can keep vitamin K elevated for days and push clotting risk back up. If you take warfarin, daily natto is not a gray area.

Heart and Circulation: What Daily Natto Is Linked To

The most striking data on daily natto comes from Japan's Takayama Study, which followed 29,079 adults for 16 years. People in the highest quartile of natto intake had a 25% lower risk of cardiovascular death and a 33% lower risk of dying from ischemic stroke — and the same benefit did not appear for other soy foods, pointing to something specific about natto.

Part of that "something" may be nattokinase, the enzyme fermentation produces. In an 8-week randomized trial, a 2,000 FU daily dose cut systolic blood pressure by about 5.55 mmHg in adults with early hypertension. A 2023 meta-analysis pooling six trials and 546 participants found smaller but consistent drops of roughly 3.45 mmHg systolic and 2.32 mmHg diastolic.

Two honest caveats belong here. First, the Takayama findings are observational, so across those 16 years they show association, not proof that natto caused the lower risk. Second, a 3-to-5 mmHg blood-pressure shift is meaningful across a population but far smaller than prescription medication achieves — so daily natto is best seen as one supportive input, not a treatment.

Gut Health, Protein, and Everyday Nutrition

Natto is a genuine fermented food, and its Bacillus subtilis cultures are unusually hardy. Research on a natto-derived strain found it tolerates stomach acid and bile salts well enough to reach the gut alive — the mechanistic basis for its probiotic reputation. Paired with the 5.4 grams of fiber in a 100-gram serving, that makes daily natto a reasonable support for digestive regularity.

As an everyday protein source, natto is efficient: its 17.7 grams of protein per 100 grams include all nine essential amino acids, and fermentation lowers the antinutrients that limit mineral absorption in raw soybeans. For a vegetarian aiming at roughly 50 grams of protein a day, one container makes a real contribution.

One detail surprises people: natto itself is very low in sodium, at about 7 milligrams per 100 grams. The salt in a natto meal comes almost entirely from the soy sauce or tare packet stirred in at the table — so seasoning lightly keeps an otherwise heart-friendly food from working against your blood pressure.

The Real Downsides of Eating Natto Every Day

Beyond the warfarin warning, daily natto carries a few smaller considerations. Among soy foods it is moderately high in purines, measured at about 56.6 milligrams per 100 grams — but the same study found that eating up to one 40-gram pack a day contributed only about 6.9% of total daily purine intake, small enough that even most people managing gout can include it in moderation.

Two groups should be cautious. Natto is made entirely from soybeans, so it is unsuitable for anyone with a soy allergy, and as a fermented food it is comparatively high in histamine, which can trigger symptoms in sensitive people. The most serious consideration is still the vitamin K one: the NIH notes that high vitamin K intake can reduce the effectiveness of warfarin, a real issue when you take in several hundred micrograms of K2 every day.

Then there is the practical hurdle. Natto's ammonia-like smell and sticky, stringy texture are famously polarizing, and for a daily habit the acquired taste is usually the real barrier — most people who stop do so over palatability, not health concerns. If you can get past it, spreading a single 40-gram serving across the week is a sustainable target; if you cannot, the enzyme itself is available in other forms.

Getting the Enzyme Without the Daily-Natto Trade-Offs

For readers drawn to nattokinase's cardiovascular research but wary of the daily K2 load, the acquired taste, or a warfarin conflict, an isolated enzyme supplement solves one specific problem: it separates the enzyme from everything else in the bean. BioAbsorb Nattokinase delivers 100 mg — 2,000 FU of enzyme activity — per capsule, the same dose used in the blood-pressure trials, taken once daily on an empty stomach.

The detail that matters most for this topic is what the formula leaves out: it is intentionally free of vitamin K2. That means it provides the fibrinolytic enzyme without the several-hundred-microgram K2 dose that makes whole natto a problem for anyone managing anticoagulation or already taking a K2 supplement. It is also allergen-free — no gluten, dairy, nuts, or shellfish — and 100% vegetarian.

On quality, every batch is third-party tested for potency and contaminants at a Canadian GMP-certified facility, and the enzyme is delivered in a DRcaps delayed-release capsule that shields it from stomach acid without the phthalates used in some enteric coatings. It is a low-cost way to get a consistent enzyme dose that a variable food serving cannot guarantee.

Frequently Asked Questions

Is it safe to eat natto every day?

For most healthy adults, yes — daily natto is eaten routinely across Japan, where a 16-year study of 29,000 adults linked higher intake to lower cardiovascular death. The clear exceptions are people on warfarin, those with a soy allergy, and anyone who is histamine-sensitive. If you take any blood thinner, check with your doctor before making natto a daily habit.

How much natto should I eat per day?

A typical Japanese serving is one 40-to-50-gram pack, and the research on daily intake suggests up to one 40-gram pack a day is sensible even for people watching uric acid. That single serving still provides several hundred micrograms of vitamin K2, so there is little reason to eat more than one pack.

Can I eat natto if I take blood thinners?

Not without medical guidance. Natto's high MK-7 content means it must be avoided by warfarin patients, because it counteracts the drug and can destabilize INR for days given MK-7's 72-hour half-life. Newer direct oral anticoagulants are less affected by dietary vitamin K, but you should still tell your prescriber about any change.

Does eating natto lower blood pressure?

It may help modestly. The enzyme nattokinase reduced systolic pressure by about 5.55 mmHg in an 8-week trial, and a meta-analysis of 546 people found reductions near 3.45 mmHg. These are small, supportive effects — not a replacement for prescribed blood-pressure treatment.

Is a nattokinase supplement as good as eating natto?

They serve different goals. Whole natto also delivers protein, fiber, and probiotics that a capsule does not, but a supplement provides a guaranteed 2,000 FU enzyme dose without the vitamin K2 load that makes daily natto risky for some people. Which is better depends on whether you want the whole food or just the enzyme.

Will eating natto every day help my bones?

The vitamin K2 in natto supports bone metabolism, and a three-year trial of 180 micrograms of MK-7 daily slowed bone-density loss in postmenopausal women. Natto is not a substitute for a full bone-health plan, but as a daily K2 source it is among the richest foods available.

The Bottom Line

Eating natto every day gives most healthy adults a genuinely useful trio — a clot-dissolving enzyme, the richest food source of vitamin K2 at nearly 998 micrograms per 100 grams, and live probiotics — with modest, research-backed support for heart and bone health. The deciding factors are the warfarin warning and whether you can tolerate the taste daily. If it is the enzyme you want without the K2 load, a standardized option like BioAbsorb Nattokinase (2,000 FU) is worth considering — and talk with your healthcare provider about what fits your situation.

Research References

1. Dietary soy and natto intake and cardiovascular disease mortality in Japanese adults: the Takayama study. American Journal of Clinical Nutrition, Vol. 105 (2017). A 16-year prospective cohort of 29,079 adults found the highest natto intake associated with 25% lower cardiovascular mortality — an effect not seen for other soy foods.
2. Effects of Nattokinase on Blood Pressure: A Randomized, Controlled Trial. Hypertension Research, Vol. 31 (2008). An 8-week double-blind trial in adults with early hypertension found a 2,000 FU daily dose reduced systolic blood pressure by about 5.55 mmHg versus placebo.
3. Nattokinase Supplementation and Cardiovascular Risk Factors: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Reviews in Cardiovascular Medicine, Vol. 24 (2023). Pooling six trials and 546 participants, nattokinase produced modest but consistent reductions in systolic and diastolic blood pressure.
4. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporosis International, Vol. 24 (2013). Daily 180 µg MK-7 slowed the age-related decline in bone mineral density and bone strength over three years.
5. First Clinical Trial of a Newly Developed, Low Menaquinone-7, Fermented Soybean Natto in Warfarin-Dependent Patients. Journal of Medicinal Food, Vol. 24 (2021). Confirms that standard natto's high MK-7 content requires warfarin patients to avoid it, and tests a specially developed low-MK-7 alternative.
6. Effects of natto intake habits on uric acid metabolism. Gout and Uric & Nucleic Acids, Vol. 48 (2024). Measured natto's purine content at 56.6 mg/100 g and found that up to one 40 g pack daily contributes little to uric acid, even in people managing gout.
7. Probiotic properties of Bacillus subtilis DG101 isolated from the traditional Japanese fermented food nattō. Frontiers in Microbiology, Vol. 14 (2023). Demonstrated that natto-derived Bacillus subtilis tolerates stomach acid and bile salts, supporting its survival in the gut.
8. Vitamin K — Micronutrient Information Center. Linus Pauling Institute, Oregon State University. Documents natto as the richest dietary source of MK-7 at 998 µg/100 g and summarizes vitamin K's role in bone and vascular health.
9. Vitamin K. Harvard T.H. Chan School of Public Health — The Nutrition Source. States the adult adequate intake for vitamin K (90–120 µg/day) and its role in blood clotting and bone health.
10. Vitamin K — Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Explains vitamin K's function in clotting-factor synthesis and its potential to reduce the effectiveness of warfarin.
11. Natto, fermented soybeans — nutrient profile. U.S. Department of Agriculture, FoodData Central (FDC ID 172443). Provides the macronutrient and mineral composition of natto, including protein, fiber, iron, and sodium.

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.