Natto: Small Beans, Big Character

Healthy Retired — Food | Article draft | 4 October 2026

Natto is one of those foods that makes an impression before you take the first bite. Its smell is distinctive, its texture is sticky, and stirring it produces long, stretchy threads. For some people, it is love at first taste. For others, the relationship needs a little negotiation.

My own way of eating it is simple: I mix natto with avocado. Sometimes I add sardines as well. The creamy avocado softens the flavour and makes the beans easier to enjoy. Healthy eating should fit your taste, not become a daily endurance test.

What is natto?

Natto is a traditional Japanese food made from cooked soybeans fermented with Bacillus subtilis var. natto. Fermentation gives it its characteristic aroma and sticky coating. It is often served with rice, mustard and a seasoning sauce, but there is no reason to limit it to a traditional Japanese breakfast. [1]

It is a whole food: you eat the beans themselves, rather than an extracted ingredient in a capsule.

What does it offer for healthy ageing?

Protein and fibre

Soybeans supply protein containing all the essential amino acids. Natto can contribute to the protein needed to maintain muscle as we grow older, especially in a diet built mainly around plants. One small packet is a contribution to a meal, rather than the entire day's protein supply.

The beans also provide fibre, which supports bowel regularity and feeds intestinal microbes. Natto brings variety alongside lentils, chickpeas, tofu and other pulses. Its advantages do not mean these familiar foods become second best.

Vitamin K2 and bones

Natto is unusually rich in vitamin K2, particularly menaquinone-7, or MK-7. Vitamin K helps activate proteins involved in normal blood clotting and bone metabolism. Small human studies have shown that eating natto raises circulating MK-7 and changes markers connected with bone metabolism. [2,3]

That is a useful nutritional reason to consider it, but it does not establish that a daily packet prevents fractures. Strong bones also depend on enough calcium, vitamin D, protein and appropriate physical activity. Claims that K2 automatically removes calcium from arteries go beyond what clinical evidence establishes. [3]

Heart health: encouraging evidence, with limits

A large Japanese study published in The BMJ followed more than 92,000 adults. Higher fermented-soy intake was associated with lower mortality, and natto intake was associated with lower cardiovascular mortality. [4]

This was an observational study. It cannot prove that natto caused those differences: people who eat it may have other helpful habits. It supports interest in natto as part of a healthy dietary pattern, rather than a promise of extra years.

Fermentation and the gut

Fermentation changes the beans and introduces bacteria and their products. However, a fermented food is not automatically a clinically proven probiotic treatment. It is sensible to enjoy natto as a fermented, fibre-containing food without claiming it cures digestive problems.

My avocado combination

For one serving, try:

  • One small packet of plain natto, typically around 40–50 g
  • Half a small avocado
  • A squeeze of lime or lemon
  • Optional chopped spring onion, mustard or a little chilli

Mash the avocado, stir the natto separately, and fold them together. Adjust the citrus and seasoning to taste. Start with less natto if its aroma is unfamiliar.

Avocado adds fibre and mostly unsaturated fat. The combination is creamy enough to eat with a spoon, spread on wholegrain toast, or serve beside vegetables. There is no established special medical synergy; it is simply a practical way to enjoy nutritious ingredients.

And sometimes sardines

For a fish-containing version, fold in two or three drained sardines. They add protein, marine omega-3 fats and vitamin B12. Sardines with edible bones also contribute calcium. This version is not vegan, but suits a mainly plant-based diet that includes fish.

Taste before adding salt: canned sardines and natto's sauce packet may already supply plenty. If avoiding added sugar, check the sauce ingredients or use your own lime and mustard instead.

Natto and medicines

People taking warfarin or another vitamin-K-antagonist medicine should discuss natto with their anticoagulation clinician before eating it. Its high vitamin K content can interfere with treatment. [3]

Nattokinase is an enzyme produced during natto fermentation, also sold as a concentrated supplement. Human evidence remains limited, and these supplements may increase bleeding risk with anticoagulant or antiplatelet medicines. They must not replace prescribed treatment. Food and concentrated supplements should not be treated as interchangeable. [5]

If you take a blood thinner, ask your pharmacist or clinician about your particular medicine before making natto a regular habit or taking nattokinase. Avoid natto if you have a soy allergy.

A place at the table

Natto earns its place through useful nutrients and culinary variety. You do not need to love it plain, and you do not need to eat it to have a healthy diet. For me, avocado—and sometimes sardines—turns a challenging flavour into a meal I enjoy. That is often what makes a good habit last.

Sources

  1. Japan Ministry of Agriculture, Forestry and Fisheries: Natto — Traditional Foods in Japan. Used for food identity and preparation, not its broader therapeutic claims.
  2. Intake of fermented soybean (natto) increases circulating vitamin K2 and gamma-carboxylated osteocalcin.
  3. NIH Office of Dietary Supplements: Vitamin K — Health Professional Fact Sheet.
  4. Katagiri et al., BMJ, 2020: Association of soy and fermented soy product intake with total and cause specific mortality.
  5. Memorial Sloan Kettering Cancer Center: Nattokinase.