Natto is written in Japanese using two characters: 納豆, meaning “stored beans”, and I have been producing it in Zielona Góra for years using exactly the same fermentation method that the Japanese have known for generations. I will tell you where this name comes from, what bacteria do to the soybean and how natto is really eaten in Japan, because the Japanese tradition has several tried and tested ways of doing it.
⚠️ Are you taking anticoagulant medication (for example acenocoumarol or warfarin)? Natto is one of the richest natural sources of vitamin K, which may affect how these medicines work. Consult your diet and supplements with a doctor. See the important legal and medical information.
In short
- Natto is a Japanese dish made from cooked soy, fermented by the bacterium Bacillus subtilis natto.
- The name is written with the characters 納豆: 納 (nō) means “to store”, and 豆 (tō) is “bean” or “grain”.
- The characteristic strings (called ito in Japanese) are a natural polymer, polyglutamic acid (PGA), with an admixture of fructan.
- In Japan, natto is most often eaten at breakfast with rice, soy sauce and karashi mustard.
- Vitamin K2 and nattokinase from natto have different legal statuses in the European Union; I write about this below.
Where the name natto comes from
In Japanese, natto is written with two characters: 納豆. The first, 納 (nō), means “to store” or “to deposit”, the second, 豆 (tō), is simply “bean” or “grain”. The name therefore refers directly to the way the dish is made: cooked soy stored under conditions that favour fermentation. Japan has a centuries-old tradition of fermenting food, from miso and soy sauce to tsukemono pickles, but each of these products ferments in a different way. Miso and soy sauce are produced by the kōji mould (Aspergillus oryzae), whereas natto ferments solely through bacteria, without any mould.
What bacteria do to the soybean
Natto is produced from cooked soy grains inoculated with the bacterium Bacillus subtilis natto. During fermentation, the bacteria break down the proteins and carbohydrates of the soy, which changes its taste, aroma and texture, making it easier to digest. A by-product of this process is the characteristic strings, described in Japanese by the word ito, literally “thread”, which stretch out when natto is stirred with a spoon. The strings are a natural polymer, polyglutamic acid (PGA), with an admixture of fructan, a polymer of fructose sugar. Both compounds form as a by-product of the bacteria’s metabolism, not as an additive to the dish.
Nattokinase and vitamin K2, different statuses in the EU
Two components of natto appear most often in discussions about its value: nattokinase and vitamin K2. It is worth separating their legal status, because it differs. Vitamin K2 MK-7 has two authorised health claims in the European Union (Regulation (EU) 432/2012): vitamin K contributes to normal blood clotting and vitamin K contributes to the maintenance of normal bones. These are the only permitted wordings in communication to the consumer. Nattokinase, the enzyme formed during the same fermentation, has no such claim (Regulation (EC) 1924/2006). Laboratory studies have described its ability to break down fibrin, but results from a test tube and animal models do not directly translate into effects in humans, which is why we do not attribute additional health benefits to it.
What natto contains
Natto is rich in nutrients. Here are the most important of them:
- Plant protein: natto provides complete protein from soy.
- Vitamin K2 (MK-7): natto is among the richest dietary sources of this form of vitamin K; I write about its legal status above.
- Live cultures of the bacterium Bacillus subtilis natto: these are responsible for the fermentation and the characteristic strings.
- Fibre: a natural component of soy grains.
- Minerals: including iron and magnesium.
How to eat natto, the Japanese breakfast ritual
In Japan, natto most often appears on the table in the morning, as part of a classic breakfast: a bowl of warm rice, natto mixed with chopsticks until thick and sticky, and a little soy sauce and a pinch of karashi mustard, the sharp Japanese mustard made from mustard seeds. This combination, rice, soy sauce and karashi, is the most traditional way to serve natto, but not the only one. It can also be eaten like this:
- With rice: the most popular way, natto mixed with soy sauce and karashi mustard on warm rice.
- In soups: as an addition to miso soup or other soups.
- With vegetables: it pairs well with cucumber, radish or spring onion.
- As an addition to salads: the strings of natto combine interestingly with cold vegetables.
Our natto in Zielona Góra
We produce natto in Zielona Góra from certified organic soy, using exactly the bacterial fermentation method I described above. If you want to understand the nature of natto, fresh natto will tell you the most about it, because it is the simplest, least processed form of the product.
Safety and precautions
Natto is a food that is safe for most healthy people, but several groups should exercise caution.
Due to its high vitamin K content, persons taking anticoagulant medicines from the vitamin K antagonist group (for example warfarin or acenocoumarol) should consult a doctor before including natto in their diet, because vitamin K affects how these medicines work. Persons taking other medicines on a regular basis should likewise exercise caution. Pregnant and breastfeeding women should also discuss natto consumption with a doctor. Natto contains soy, so it is not suitable for persons with a soy allergy. A food does not replace a varied diet or medical advice.
Summary
Natto (納豆) is a Japanese dish made from fermented soy whose name describes directly how it is made: a grain stored for fermentation by the bacterium Bacillus subtilis natto. The characteristic strings are a natural polymer PGA with fructan, and traditionally it is eaten at breakfast with rice, soy sauce and karashi mustard. It is a valuable food, a source of plant protein, fibre and vitamin K2, but not a medicine or supplement, and has its place in a varied diet.
Frequently asked questions
What is natto?
Natto is a traditional Japanese dish made from cooked soy fermented by the bacterium Bacillus subtilis natto. It is written with the characters 納豆, literally “stored beans”, and is characterised by a stringy texture and a pronounced umami taste.
Where do the characteristic strings in natto come from?
They are a natural polymer, polyglutamic acid (PGA), with an admixture of fructan, formed as a by-product of bacterial fermentation. The longer natto is stirred, the more visible the strings become.
How is natto traditionally eaten in Japan?
Most often at breakfast, mixed with soy sauce and karashi mustard, served on warm rice. Natto also works well in miso soup, with vegetables or as an addition to salads.
Does natto have confirmed health effects in the European Union?
Partially. Vitamin K2 has such claims (Regulation (EU) 432/2012), but they concern vitamin K only, not the whole product. Nattokinase, the second well-known component of natto, has no authorised health claim in the EU (Regulation (EC) 1924/2006), which is why in our communication about natto we distinguish between these two components, rather than speaking generally about the “effects of natto”.
Who should be cautious about eating natto?
Persons taking anticoagulant medicines, pregnant and breastfeeding women, and persons with a soy allergy should consult a doctor before consuming natto, due to its vitamin K content and the presence of soy.
Where to buy natto in Poland?
Our natto, produced in Zielona Góra, can be bought directly in our online shop at natto.pl.
Sources
- Regulation (EC) No 1924/2006 on nutrition and health claims made on foods, text on EUR-Lex
- Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods, text on EUR-Lex
- EU Register on nutrition and health claims, European Commission
Legal and medical note. This article is educational and does not replace the advice of a doctor or pharmacist. Nattokinase has no authorised health claim in the European Union (Regulation (EC) 1924/2006), and natto is a food, not a medicine or supplement, and does not replace a varied diet. Full information is on the Legal and medical information page.
