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Natto

Also known as Fermented soybeans, Itohiki natto

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Whole soybeans fermented with Bacillus subtilis var. natto, which produces the sticky polyglutamic acid strands and pungent aroma it is known for. It is by a wide margin the richest known dietary source of vitamin K2 as MK-7.

Bone HealthHeart HealthGut & Digestive Health

Potential health benefits

Best supported: Moderate

Ordered by how well the human research supports them — strongest first. A rating describes the state of the evidence, not how impressive the food is. How we rate evidence.

Bone mineral density

Bone Health
Moderate evidence

Research suggests vitamin K2 intake is associated with bone density and turnover markers, with several Japanese trials and cohorts reporting benefit at natto-level intakes. Results outside Japan have been less consistent and fracture data remains limited.

What may be going on: Vitamin K2 is the cofactor that carboxylates osteocalcin, the protein that binds calcium into bone matrix.

Moderate evidence. Several human studies point the same way, with real caveats.

3 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Cardiovascular risk markers

Heart Health
Insufficient evidence

Evidence is limited for natto affecting cardiovascular outcomes. The claim comes from nattokinase, an enzyme sold as a concentrated supplement and tested at doses unrelated to eating natto; the food itself has not been trialled for these endpoints.

Insufficient evidence. Not enough human research to say anything useful yet.

No source is attached to this association yet, so it is rated insufficient by default. It is listed because people commonly ask about it — not because there is evidence for it.

Gut microbiome

Gut & Digestive Health
Insufficient evidence

Some trials report changes in gut bacterial composition with Bacillus subtilis intake. The organism is a spore former that survives stomach acid well, but human data using natto as the food is limited.

Insufficient evidence. Not enough human research to say anything useful yet.

No source is attached to this association yet, so it is rated insufficient by default. It is listed because people commonly ask about it — not because there is evidence for it.

Ask about Natto

Ask about Natto

Answers are written only from the entries on this page — the same nutrients, compounds, claims and citations you can read above. Nothing is added from outside the database, and every answer lists what it was built from.

AI explanations are not switched on for this site, so there is nothing to ask here. Everything above is read straight from the database and does not need them.

Key nutrients

Nutrient content per 100 grams
NutrientAmount% DV
Macronutrients
Calories211 kcal11%
Protein19.4 g39%
Total fat11 g14%
Carbohydrate12.7 g5%
Fibre5.4 g19%
Total sugars4.89 g—
Water55 g—
Fats
Saturated fat1.59 g8%
Monounsaturated fat2.43 g—
Polyunsaturated fat6.21 g—
Cholesterol0 mg0%
EPA (omega-3)0 g—
DHA (omega-3)0 g—
DPA (omega-3)0 g—
Linoleic acid (omega-6)5.48 g—
Vitamins
Vitamin A0 µg0%
Vitamin C13 mg14%
Vitamin D0 µg0%
Vitamin E0.01 mg0%
Vitamin K23.1 µg19%
Thiamin (B1)0.16 mg13%
Riboflavin (B2)0.19 mg15%
Niacin (B3)0 mg0%
Pantothenic acid (B5)0.215 mg4%
Vitamin B60.13 mg8%
Folate8 µg2%
Vitamin B120 µg0%
Choline57 mg10%
Minerals
Calcium217 mg17%
Iron8.6 mg48%
Magnesium115 mg27%
Phosphorus174 mg14%
Potassium729 mg16%
Sodium7 mg0%
Zinc3.03 mg28%
Copper0.667 mg74%
Manganese1.53 mg66%
Selenium8.8 µg16%
Other measured compounds
Beta-carotene0 µg—
Alpha-carotene0 µg—
Lycopene0 µg—
Lutein + zeaxanthin0 µg—
Caffeine0 mg—
Ash1.9 g—

Nutrient values are per 100 g of the USDA reference entry named on this page and vary with variety, growing conditions, storage and preparation.

Source record: Natto (USDA FoodData Central, FDC ID 172443).

% DV uses the FDA Daily Values for adults and children aged 4 and over. A dash means no Daily Value has been established for that nutrient.

Bioactive compounds

Compounds present in meaningful amounts. Presence is banded rather than quantified, because whole-food levels vary enormously with variety, growing conditions, storage and preparation.

How preparation changes things

Only effects with real support are listed. If a preparation method is missing, it is because nothing dependable is documented — not because it makes no difference.

  • fermentedIncreases vitamin K2 (MK-7)

    Bacillus subtilis synthesises MK-7 during fermentation, so the vitamin K2 in natto is created by the process rather than present in the soybean.

  • fermentedReduces phytates

    Fermentation reduces the phytate content of the soybeans, which improves absorption of iron and zinc from the same meal.

Things to know

Allergies, interactions and intake concerns. Every food gets this section — a reference where everything is uniformly good is not a reference.

  • Avoid

    Vitamin K2 and warfarin

    Natto contains enough MK-7, with a long half-life, that even a single serving can suppress the anticoagulant effect of warfarin for days. It is specifically contraindicated for people on vitamin K antagonists, not merely something to keep consistent.

  • Allergy

    Soy allergy

    Soy is a major regulated allergen. Separately, rare delayed anaphylaxis to natto has been reported and attributed to its polyglutamic acid.

  • Too much

    Sodium in the supplied sauce

    The soy sauce and mustard sachets packed with natto add most of the sodium in a typical serving; the beans themselves are not especially salty.

  • Worth knowing

    Isoflavones and levothyroxine timing

    As with other soy foods, isoflavones can reduce levothyroxine absorption if eaten at the same time as the dose.