💡 What You Need to Know Right Away
- Natto consumption reduces systolic and diastolic blood pressure according to a meta-analysis of 6 randomized controlled trials with 546 participants[Evidence: A][1]
- Natto significantly improves femoral neck bone mineral density based on a systematic review of 3 prospective studies with 1,658 participants[Evidence: A][2]
- Nattokinase at 10,800 FU/day effectively managed atherosclerosis progression with improvement rates of 66.5-95.4% in a study of 1,062 participants[Evidence: B][4]
- Daily nattokinase (100 mg) reduced diastolic blood pressure from 86 mmHg to 81 mmHg in male participants in an 8-week RCT[Evidence: B][5]
If you've been searching for a natural way to support your heart and bone health, you've likely come across natto—the traditional Japanese fermented soybean food that's been consumed for over 1,000 years. But does this sticky, stringy superfood actually deliver on its health promises?
The answer is yes, backed by solid science. Researchers have published dozens of clinical studies examining natto's effects on cardiovascular health, bone density, and metabolic function. This guide breaks down exactly what the research shows, how much you should consume, and important safety considerations you need to know.
You'll discover the mechanisms behind natto's unique health benefits, evidence-based dosage recommendations, and practical tips for incorporating this nutrient-dense food into your diet—even if you're a complete beginner to Japanese cuisine.
❓ Quick Answers
What is natto and what is it good for?
Natto is a traditional Japanese food made from soybeans fermented by Bacillus subtilis bacteria. It's exceptionally rich in vitamin K2 (menaquinone-7), nattokinase enzyme, and protein. Research shows natto supports cardiovascular health by reducing blood pressure and may help prevent osteoporosis through improved bone mineral density.[Evidence: A][1][2]
Is it safe to eat natto everyday?
Yes, daily natto consumption is safe for most healthy adults. Toxicological studies found no adverse effects in 28-day and 90-day trials, with a favorable safety profile for regular oral consumption.[Evidence: C][8] However, people taking blood-thinning medications should consult their doctor due to natto's high vitamin K content.
How much natto should you eat per day?
For general health benefits, consuming 1-2 packs (approximately 40-100 grams) of natto per day is commonly recommended. Studies showing fracture prevention benefits used ≥7 packs weekly.[Evidence: C][3] For cardiovascular benefits via supplements, studies used 100 mg nattokinase (approximately 2,000 FU) daily.[Evidence: B][5]
Does natto lower blood pressure?
Yes, natto and nattokinase supplements reduce blood pressure. A meta-analysis of 6 randomized controlled trials with 546 participants found nattokinase reduces both systolic and diastolic blood pressure.[Evidence: A][1] One RCT showed diastolic pressure dropped from 86 to 81 mmHg in male participants.[Evidence: B][5]
Is natto good for bone health?
Yes, natto strongly supports bone health. A systematic review of studies with 1,658 participants found natto significantly improved femoral neck bone mineral density.[Evidence: A][2] Women consuming ≥7 packs weekly showed a 0.56 hazard ratio for fractures—meaning 44% lower fracture risk.[Evidence: C][3]
Natto: The Superfood Secret
A traditional Japanese staple of fermented soybeans. Beyond its unique texture lies a nutritional profile unmatched by almost any other plant-based food.
🔬 How Does Natto Work? The Science Explained
Understanding how natto benefits your body requires looking at its unique bioactive compounds. Unlike other soy foods, natto undergoes fermentation by Bacillus subtilis var. natto, which produces several powerful compounds not found in unfermented soybeans.
Nattokinase: Your Blood's Natural Helper
Think of nattokinase as molecular scissors cutting through fibrin—the protein mesh that forms blood clots. This fibrinolytic enzyme directly breaks down clots and also activates your body's own clot-dissolving systems. A clinical study with 1,062 participants demonstrated that nattokinase at 10,800 FU/day effectively managed atherosclerosis progression with improvement rates ranging from 66.5% to 95.4% in carotid artery thickness and plaque size.[Evidence: B][4]
The cardiovascular benefits extend beyond clot prevention. Research shows nattokinase consumption reduces von Willebrand factor—a cardiovascular risk marker—particularly in women. It also appears to influence plasma renin activity, with 66% of participants showing increased activity compared to just 8% in the placebo group.[Evidence: B][5]
Vitamin K2 (Menaquinone-7): The Calcium Director
Imagine calcium as delivery trucks and vitamin K2 as the traffic controller directing them to the right destination—your bones instead of your arteries. Natto contains the highest dietary concentration of menaquinone-7 (MK-7), the most bioavailable form of vitamin K2. This vitamin activates osteocalcin, the protein responsible for binding calcium into bone matrix.
A systematic review examining bone mineral density effects found that natto significantly improved femoral neck BMD, though results for lumbar spine were mixed between Asian cohort studies and Caucasian RCT populations.[Evidence: A][2]
Gamma-Polyglutamic Acid (γ-PGA): Blood Sugar Regulation
The sticky, stringy texture of natto comes from γ-polyglutamic acid, a biopolymer produced during fermentation. Animal studies indicate that γ-PGA may reduce fasting blood glucose, regulate lipid metabolism, and improve insulin resistance through glucose metabolism modulation.[Evidence: C][10]
Polyamines: Spermidine and Spermine
Natto is exceptionally rich in polyamines, particularly spermidine and spermine. These compounds have gained research attention for potential anti-aging effects. A 12-month randomized controlled trial examined spermidine supplementation in older adults with subjective cognitive decline. While the primary endpoint showed no significant changes in mnemonic discrimination performance, exploratory analyses suggested possible improvements in verbal memory and inflammation markers.[Evidence: B][9]
However, it's important to note that this study used purified spermidine supplements rather than natto consumption, so direct translation to whole food benefits requires further research.
📊 Dosage and How to Use Natto
The optimal natto dosage depends on your health goals. Clinical research provides specific guidance for different purposes:
| Purpose/Condition | Dosage | Duration | Evidence |
|---|---|---|---|
| Cardiovascular/Atherosclerosis Management | 10,800 FU/day nattokinase | 12 months | [B][4] |
| Blood Pressure Reduction | 100 mg nattokinase daily | 8 weeks | [B][5] |
| Fracture Prevention (Bone Health) | ≥7 packs natto weekly (~50g each) | Long-term (observational) | [C][3] |
| Cognitive Function/Aging | 20 mg spermidine daily | 12 months | [B][9] |
Natto Food vs. Nattokinase Supplements
Whole natto food provides a complete nutritional package including vitamin K2, protein, probiotics, and fiber—not just nattokinase. However, supplements offer standardized dosing measured in Fibrinolytic Units (FU). Studies showing cardiovascular benefits used high-dose supplements (10,800 FU/day), while lower doses (3,600 FU/day) proved ineffective for atherosclerosis management.[Evidence: B][4]
Best Time to Eat Natto
Traditional Japanese practice suggests eating natto in the morning with rice. However, for cardiovascular effects, some evidence suggests evening consumption may be beneficial since fibrinolytic activity is naturally lower at night and blood clot risk is higher in early morning hours. There is no clinical consensus on optimal timing.
Maximum Intake Recommendation
The highest effective dose studied was 10,800 FU/day nattokinase in the atherosclerosis management trial with 1,062 participants, which reported no adverse effects.[Evidence: B][4] For whole food natto, no upper limit has been established for healthy adults, though moderation is advised for those on anticoagulant therapy.
⚠️ Risks, Side Effects, and Warnings
⚠️ Important Safety Information
- Blood Thinner Interaction: Natto's high vitamin K2 content can reduce warfarin efficacy. Nattokinase may also potentiate bleeding risk when combined with anticoagulants or antiplatelet medications.
- Immunocompromised Children: Natto consumption is contraindicated for children undergoing chemotherapy due to documented risk of Bacillus subtilis bacteremia.[Evidence: C][12]
- Soy Allergy: Documented cases of IgE-mediated anaphylaxis from natto consumption, with late-onset reactions possible up to 12 hours post-ingestion.[Evidence: D][11]
General Safety Profile
Toxicological assessment of nattokinase derived from Bacillus subtilis var. natto found no adverse effects in 28-day and 90-day subchronic toxicity studies. High-dose rodent testing showed low toxicological concern, supporting a favorable safety profile for oral consumption.[Evidence: C][8]
In the large clinical study with 1,062 participants taking nattokinase at 10,800 FU/day for 12 months, no noticeable adverse effects were recorded.[Evidence: B][4]
Who Should Avoid Natto?
- People taking anticoagulants (warfarin, heparin): Vitamin K antagonism may reduce drug efficacy; nattokinase may increase bleeding risk
- Individuals with soy allergies: Risk of allergic reaction including anaphylaxis
- Immunocompromised patients: Especially children on chemotherapy due to bacteremia risk[12]
- Pre-surgery patients: Discontinue nattokinase supplements at least 2 weeks before scheduled surgery due to bleeding concerns
Pregnancy and Lactation
Limited safety data exists for natto consumption during pregnancy and lactation. No specific post-2015 clinical studies were identified addressing these populations. Consult your healthcare provider before consuming natto or nattokinase supplements if you are pregnant, planning pregnancy, or breastfeeding.
Common Side Effects
Most people tolerate natto well. Potential side effects are generally mild:
- Digestive discomfort (bloating, gas) when first introducing fermented foods
- Strong taste and odor may cause nausea in unaccustomed individuals
- Skin reactions in those with soy sensitivity
🥗 Practical Ways to Use Natto
1. Traditional Japanese Style
The classic preparation serves natto over warm rice. Open the pack, remove the sauce and mustard packets, and stir vigorously (50-100 times) to develop the characteristic stringy texture. Add the included soy sauce and mustard, then place over a bowl of freshly cooked rice. The heat from the rice softens the flavor and makes it more approachable for beginners.
2. Smoothie Integration
For those who struggle with natto's texture and smell, blending 1-2 tablespoons into a fruit smoothie effectively masks the flavor. Combine with banana, berries, and almond milk. The strong fruit flavors overpower natto's pungency while you still receive the nutritional benefits.
3. Natto Toast
Spread natto on buttered toast with a drizzle of soy sauce. The fat from butter and the crunch of toast create a texture combination that many find more palatable than the traditional rice preparation. Add sliced green onions or a fried egg for additional flavor.
Taste Adaptation Tips
- Start small: Begin with half a pack mixed heavily with rice
- Choose small beans: Smaller natto beans (kogome natto) have a milder flavor than large beans
- Add flavor maskers: Kimchi, raw egg, sesame oil, or chili oil can help
- Freeze before eating: Slightly frozen natto has reduced odor
- Give it 5 tries: Taste preferences for fermented foods typically adapt within 5-10 exposures
Storage and Quality
Fresh natto is typically sold frozen and should be stored in the freezer until ready to use. Once thawed, consume within 1-2 weeks and keep refrigerated. The fermentation continues slowly even when refrigerated, so older natto develops a stronger ammonia smell. White surface crystals indicate aged natto—still safe but more intense in flavor.
Where to Buy
Look for natto in the frozen section of Asian grocery stores, Japanese supermarkets, or health food stores. Online retailers also ship frozen natto. When selecting, look for products with minimal ingredients: soybeans and Bacillus subtilis culture only.
⚖️ Natto vs. Other Fermented Soy Foods
Natto is just one of several fermented soybean products. Understanding the differences helps you choose the right food for your health goals.
| Feature | Natto | Tempeh | Miso |
|---|---|---|---|
| Fermentation Organism | Bacillus subtilis bacteria | Rhizopus mold | Aspergillus mold + salt |
| Vitamin K2 Content | Very High (1,000+ mcg/100g) | Low | Moderate |
| Nattokinase | Yes (unique) | No | No |
| Protein per 100g | 18g | 19g | 12g |
| Probiotic Benefit | Bacillus subtilis (spore-forming) | Limited (cooking destroys) | Limited (high salt, cooking) |
| Texture | Sticky, stringy | Firm, chewy | Paste |
| Best For | Heart health, bone health | Protein intake, meat substitute | Seasoning, soup base |
| Cardiovascular Research | Strong (multiple RCTs) | Limited | Limited |
Why Natto Stands Out
Natto is the only common food containing nattokinase—the fibrinolytic enzyme responsible for its unique cardiovascular benefits. While other soy foods provide protein and isoflavones, only natto delivers the specific compounds studied in blood pressure and atherosclerosis research.[Evidence: A][1]
Additionally, natto's vitamin K2 content (specifically menaquinone-7) far exceeds other fermented soy products. This makes natto particularly valuable for bone health compared to tempeh or miso.
Natto Food vs. Nattokinase Supplements
Nattokinase supplements provide standardized enzyme doses without the taste challenge of whole natto. However, supplements lack the vitamin K2, complete protein, probiotics, and fiber found in whole food natto. For comprehensive nutritional benefits, whole food consumption is preferred. For targeted high-dose cardiovascular intervention, supplements may be more practical.
Frequently Asked Questions
What are the side effects of natto?
Natto is well-tolerated by most people, with toxicological studies confirming a favorable safety profile and no adverse effects in 28-90 day trials. The most common issues are digestive discomfort (bloating, gas) during initial consumption and difficulty with the strong taste and smell. Serious adverse effects are rare but include allergic reactions in soy-sensitive individuals—IgE-mediated anaphylaxis has been documented, with late-onset reactions possible up to 12 hours after eating. People taking blood thinners should avoid natto due to vitamin K interactions and potential bleeding risk from nattokinase.
Does natto have vitamin K2?
Yes, natto contains exceptionally high levels of vitamin K2, specifically in the menaquinone-7 (MK-7) form. Natto provides approximately 1,000+ mcg of vitamin K2 per 100 grams—far more than any other common food source. This makes natto the single best dietary source of MK-7. The vitamin K2 in natto is responsible for its bone health benefits, as it activates osteocalcin protein which binds calcium into bone matrix. A systematic review confirmed that natto consumption significantly improved femoral neck bone mineral density. However, this high vitamin K content is why natto is contraindicated for people on warfarin—it can reduce the drug's anticoagulant effect.
Does natto interact with blood thinners?
Yes, natto has significant interactions with blood-thinning medications. There are two interaction mechanisms: First, natto's high vitamin K2 content directly antagonizes warfarin, reducing its anticoagulant effectiveness. Second, nattokinase enzyme has its own blood-thinning properties through fibrinolytic activity, which may potentiate bleeding risk when combined with anticoagulants (warfarin, heparin) or antiplatelet drugs (aspirin, clopidogrel). Clinical research has noted nattokinase's heparin-binding affinity. If you take any blood-thinning medication, consult your doctor before consuming natto or nattokinase supplements. If consumption is approved, maintain consistent intake levels so medication dosing can be adjusted accordingly.
Is natto good for your gut?
Natto supports gut health through its probiotic content. The Bacillus subtilis bacteria used in natto fermentation is a spore-forming probiotic that survives stomach acid better than many other probiotic strains. Once in the intestines, these bacteria may contribute to microbiome diversity. However, clinical evidence specifically for natto's gut health benefits is less robust than for its cardiovascular and bone effects. The primary probiotic research on natto relates to general immune function rather than digestive conditions. For targeted gut health benefits, natto can be part of a broader fermented food strategy alongside yogurt, kefir, and kimchi. Note that immunocompromised individuals should avoid natto due to bacteremia risk.
Can you eat natto while pregnant?
There is limited clinical safety data specifically addressing natto consumption during pregnancy. No post-2015 studies were identified examining pregnancy outcomes with natto intake. While natto is a traditional food consumed safely in Japan for centuries, including during pregnancy, controlled clinical research is lacking. The high vitamin K2 content is generally considered beneficial for fetal bone development, and soy isoflavones are typically safe in food amounts. However, if you are pregnant or planning pregnancy, consult your healthcare provider before adding natto to your diet, especially if you're not accustomed to it. Nattokinase supplements should be approached with extra caution due to their blood-thinning properties.
Does natto help with weight loss?
Direct clinical evidence for natto-induced weight loss in humans is limited. Natto is relatively low in calories and high in protein (18g per 100g), which may support satiety and muscle maintenance during weight management. Animal research on γ-polyglutamic acid (a natto component) showed effects on glucose and lipid metabolism, including improved insulin resistance. The connection between natto consumption and tooth loss through bone mineral density pathways in postmenopausal women suggests metabolic benefits, though not directly weight-related. For weight loss goals, natto can be a nutritious protein source as part of an overall healthy diet, but should not be relied upon as a primary weight loss intervention.
Our Accuracy Commitment and Editorial Principles
At Biochron, we take health information seriously. Every claim in this article is supported by peer-reviewed scientific evidence from reputable sources published in 2015 or later. We use a rigorous evidence-grading system to help you understand the strength of research behind each statement:
- [Evidence: A] = Systematic review or meta-analysis (strongest evidence)
- [Evidence: B] = Randomized controlled trial (RCT)
- [Evidence: C] = Cohort or case-control study
- [Evidence: D] = Expert opinion or clinical guideline
Our editorial team follows strict guidelines: we never exaggerate health claims, we clearly distinguish between correlation and causation, we update content regularly as new research emerges, and we transparently note when evidence is limited or conflicting. For our complete editorial standards, visit our Editorial Principles page.
This article is for informational purposes only and does not constitute medical advice. Always consult qualified healthcare professionals before making changes to your health regimen, especially if you have medical conditions or take medications.
References
- 1 . Nattokinase Supplementation and Cardiovascular Risk Factors: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Li X, Long J, Gao Q, Pan M, Wang J, Zhang Y. Reviews in Cardiovascular Medicine, 2023. DOI | PubMed [Evidence: A]
- 2 . The Anti-osteoporosis Effects of Natto on Bone Mineral Density in Perimenopausal Women. Liu Y, He Y, He B, Kong L. Current Medical Chemistry, 2021. DOI | PubMed [Evidence: A]
- 3 . Natto Intake is Inversely Associated with Osteoporotic Fracture Risk in Postmenopausal Japanese Women. Kojima A, Ikehara S, Kamiya K, et al. Journal of Nutrition, 2020. DOI | PubMed [Evidence: C]
- 4 . Effective management of atherosclerosis progress and hyperlipidemia with nattokinase: A clinical study with 1,062 participants. Chen H, Chen J, Zhang F, et al. Frontiers in Cardiovascular Medicine, 2022. DOI | PubMed [Evidence: B]
- 5 . Consumption of nattokinase is associated with reduced blood pressure and von Willebrand factor, a cardiovascular risk marker: results from a randomized, double-blind, placebo-controlled, multicenter North American clinical trial. Jensen GS, Lenninger M, Ero MP, Benson KF. Integrative Blood Pressure Control, 2016. DOI | PubMed [Evidence: B]
- 6 . A 5-year longitudinal association between dietary fermented soya bean (natto) intake and tooth loss through bone mineral density in postmenopausal women: The Yokogoshi cohort study. Iwasaki M, Sato M, Yoshihara A, et al. Gerodontology, 2021. DOI | PubMed [Evidence: C]
- 7 . Nattokinase atherothrombotic prevention study: A randomized controlled trial. Hodis HN, Mack WJ, Meiselman HJ, et al. Clinical Hemorheology and Microcirculation, 2021. DOI | PubMed [Evidence: B]
- 8 . Toxicological assessment of nattokinase derived from Bacillus subtilis var. natto. Lampe BJ, English JC. Food and Chemical Toxicology, 2016. DOI | PubMed [Evidence: C]
- 9 . Effects of Spermidine Supplementation on Cognition and Biomarkers in Older Adults With Subjective Cognitive Decline: A Randomized Clinical Trial. Schwarz C, Benson GS, Horn N, et al. JAMA Network Open, 2022. DOI | PubMed [Evidence: B]
- 10 . Antidiabetic effects and mechanism of γ-polyglutamic acid on type II diabetes mice. Li Y, Zhang W, Tang C, et al. International Journal of Biological Macromolecules, 2024. DOI | PubMed [Evidence: C]
- 11 . Anaphylaxis from nattokinase in a patient with fermented soybean (natto) allergy. Awatani-Yoshidome K, Hashimoto T, Satoh T. Allergology International, 2022. DOI | PubMed [Evidence: D]
- 12 . Natto intake is a risk factor of Bacillus subtilis bacteremia among children undergoing chemotherapy for childhood cancer: A case-control study. Aoyagi R, Okita K, Uda K, et al. Journal of Infection and Chemotherapy, 2023. DOI | PubMed [Evidence: C]
Medical Disclaimer
This content is for informational and educational purposes only. It is not intended to provide medical advice or to take the place of such advice or treatment from a personal physician. All readers are advised to consult their doctors or qualified health professionals regarding specific health questions and before making any changes to their health routine, including starting new supplements.
Neither Biochron nor the author takes responsibility for possible health consequences of any person reading or following the information in this educational content. All readers, especially those taking prescription medications, should consult their physicians before beginning any nutrition, supplement, or lifestyle program.
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