Natto
Food · Legume · Food, Typed Supps
Natto is sticky fermented soybeans loaded with vitamin K2, a nutrient that helps your body put calcium into bones instead of blood vessels.
Stage by stage
- Sticky Start (Mouth): Natto's sticky strands of gamma-glutamic acid coat each fermented soybean, releasing a pungent, ammonia-tinged aroma and an intensely slippery texture as you chew.
- Acid Passage (Stomach): Stomach acid and pepsin break down most dietary protein, including much of the nattokinase enzyme, though the spore-forming Bacillus subtilis bacteria used in fermentation are built to survive this acidic passage.
- K2 Absorption (Small Intestine): In the small intestine, vitamin K2 (menaquinone-7) is packaged with dietary fat into micelles and absorbed into the lymphatic system, while surviving Bacillus subtilis spores can continue producing small amounts of vitamin K2 further down the gut.
- Bone & Artery Support (Bone & Blood Vessels): Absorbed MK-7 travels via chylomicrons to the liver and then to bone and blood vessels, where it helps activate osteocalcin and matrix Gla protein, proteins that direct calcium into bone and away from artery walls.
Timing
Vitamin K2 is fat-soluble, so eating natto alongside a source of dietary fat, such as its packaged sauce or added sesame oil, improves absorption.
Time to effect
- Hours to months: Blood vitamin K2 rises within hours of eating natto, but measurable improvements in bone turnover markers from regular consumption take weeks to months to appear in research studies.
Allergens
Contains: Soya. Derived from what this food is, not from a product label.
Eating patterns
Fits: Vegan, Vegetarian, Pescatarian, Halal, Kosher, Gluten-free. Depends on the product: Keto, Low-FODMAP.
Satiety
160 on the satiety index, where white bread is 100 — high. Modelled from the Holt et al. (1995) measurements.
Environmental footprint
3.2 kg CO2e and 149 litres of freshwater per kg, matched to "Tofu" in Poore & Nemecek (2018), Science 360.
Cost band
Mid — roughly £7 per kg, as a band midpoint rather than a price.
Key nutrients
Nutrition per 100g
- Calories: 212
- Protein: 19.4g
- Carbohydrate: 14.4g
- of which sugars: 0g
- Fat: 11g
- of which saturated: 1.6g
- Fibre: 5.4g
- Sodium: 7mg
Food vs. supplement
Natto delivers vitamin K2 inside a whole soy food matrix with fiber, protein, and live bacteria, while isolated vitamin K2 or nattokinase supplements provide a single standardized compound and can't replicate that combination.
Kitchen tip
Stir natto vigorously before eating to break up its sticky strands, and if you take warfarin, discuss consistent natto intake with your prescriber since even boiling only partially blunts its vitamin K content.
Common myth
"Natto and its nattokinase are basically a natural blood thinner, so it's a safe heart-health food for everyone." In reality: Natto is actually rich in vitamin K, which promotes clotting and directly antagonizes warfarin and other vitamin K antagonist medications; people taking those drugs need medical guidance on natto intake, and nattokinase supplements carry their own theoretical bleeding-risk interactions with anticoagulant and antiplatelet drugs.
Recipes that use it
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