Natto: Benefits, Nutrition, and Why It Is Rich in Vitamin K2

In this article

1. What is natto and where does it come from?
2. How is natto made?
3. What nutrients does natto contain?
4. Why is natto so rich in vitamin K2?
5. What are the potential benefits of natto?
6. What is the connection between natto and bone health?
7. What is the connection between natto and cardiovascular health?
8. What is nattokinase, and is it the same as natto?
9. Can natto support gut health?
10. How much natto can we eat and how is it served?
11. How is natto different from miso, tempeh, and other fermented soy foods?
12. Who should be cautious with natto?
13. Frequently asked questions
14. Final thoughts

Natto is a traditional Japanese food made from fermented soybeans. It has a distinctive sticky texture, forms long strings when stirred, and has a strong aroma and flavor that can be unfamiliar to people trying it for the first time.

From a nutritional perspective, natto is particularly interesting because it provides plant protein, fiber, and several minerals. Fermentation also produces compounds such as vitamin K2, especially menaquinone-7 (MK-7), and the enzyme nattokinase.

Natto has been studied in relation to bone health, cardiovascular health, and the gut microbiota. However, the evidence is not equally strong for all of these effects, and research on natto as a food should be distinguished from studies using concentrated nattokinase supplements.

What is natto and where does it come from?

Natto is a traditional Japanese food made from fermented soybeans. The best-known variety is itohiki natto, which has a sticky consistency and develops long, string-like threads when the beans are stirred.

Natto belongs to a broader group of fermented Asian soy foods, but its fermentation process differs from those used to make foods such as miso or tempeh. Its characteristic microorganism is Bacillus subtilis var. natto.

Fermentation creates natto’s distinctive flavor and texture, but it also changes the composition of the soybeans. Compounds associated with this process include vitamin K2 and the enzyme nattokinase.

How is natto made?

To make traditional natto, soybeans are first soaked and cooked. They are then inoculated with Bacillus subtilis var. natto and kept under controlled conditions while fermentation takes place.

During fermentation, the bacteria use components of the soybeans and produce various enzymes and metabolites. This process also creates the characteristic sticky, stringy texture of natto.

Fermentation does more than simply preserve the soybeans. It changes the structure and composition of the food and contributes to the formation of bioactive compounds that are not found in the same amounts in unfermented soybeans.

One of the most notable compounds produced during this process is menaquinone-7 (MK-7). MK-7 is a form of vitamin K2 and one of the nutritional characteristics that makes natto unusual among common foods.

What nutrients does natto contain?

Because natto is made from soybeans, it is naturally rich in plant protein. It also provides fiber, predominantly unsaturated fats, and a range of minerals.

The values below are approximate amounts per 100 g of natto. Nutrient content can vary depending on the soybeans, bacterial culture, and production method.

Nutrient	Approximate amount per 100 g
Energy	211 kcal
Protein	19.4 g
Fat	11 g
Carbohydrates	12.7 g
Fiber	5.4 g
Calcium	217 mg
Magnesium	115 mg
Potassium	729 mg
Iron	8.6 mg
Zinc	3 mg
Copper	0.67 mg
Manganese	1.5 mg

These values show that natto should not be viewed only as a source of vitamin K2. It is a nutrient-dense food that combines protein and fiber with several important minerals.

Nutrition databases do not always separate vitamin K1 accurately from the different forms of vitamin K2. Studies that directly measure MK-7 in natto therefore often report much higher values than generic “vitamin K” figures found in some food databases.

Why is natto so rich in vitamin K2?

One of natto’s most unusual nutritional characteristics is its high concentration of menaquinone-7, or MK-7, a form of vitamin K2. MK-7 is produced during fermentation as a result of bacterial activity.

This means that ordinary soybeans and fermented natto do not have the same vitamin K2 profile. The fermentation process is responsible for much of natto’s unusually high MK-7 content.

Studies have reported approximately 775–865 mcg of MK-7 per 100 g in some types of traditional natto. Specially enriched products may contain even higher amounts, although the exact concentration varies by product and fermentation method.

Vitamin K is required to activate several vitamin K-dependent proteins. These include osteocalcin, which is involved in bone metabolism, and matrix Gla protein (MGP), which is studied for its role in vascular tissues.

This high MK-7 content is one reason natto frequently appears in research examining vitamin K2 and bone health. It also makes natto nutritionally different from many other fermented soy products.

What are the potential benefits of natto?

One of the clearest nutritional advantages of natto is the combination of protein, fiber, minerals, and vitamin K2 in a single food. This nutritional profile can make it a useful component of a varied diet.

Researchers have also investigated whether regular natto consumption may be associated with additional health effects. The most commonly studied areas include:

• bone metabolism;
• cardiovascular health;
• vitamin K2 intake and status;
• digestion and the gut microbiota.

However, the strength of the evidence differs considerably between these areas. Some findings come from observational studies conducted in Japan, which can identify associations but cannot prove that natto itself caused the outcome.

This distinction is important when discussing possible benefits. Natto can be considered a nutritious fermented food without presenting it as a treatment for conditions that have not been shown to respond directly to natto consumption.

What is the connection between natto and bone health?

The relationship between natto and bone health is one of the most interesting areas of research, largely because of natto’s high MK-7 content. Vitamin K is required for the carboxylation of osteocalcin, a protein produced by bone cells and involved in bone metabolism.

Adequate vitamin K allows osteocalcin to function normally. This biological relationship has led researchers to investigate whether eating natto may be associated with bone-health outcomes.

One study involving 1,662 Japanese men aged 65 or older found that higher natto consumption was associated with greater bone mineral density at the hip and femoral neck. When researchers adjusted the results for a marker of vitamin K status, the association disappeared, suggesting that vitamin K may explain an important part of the observed relationship.

A later meta-analysis including 2,327 participants from Japanese studies also found associations between habitual natto intake, higher blood levels of MK-7, and a more favorable profile for some markers of bone metabolism. The authors nevertheless noted that much of the available evidence is observational, and certainty remains low for some bone-density outcomes.

Natto can therefore be considered a valuable dietary source of vitamin K2. The available evidence does not establish natto as a treatment for osteoporosis.

What is the connection between natto and cardiovascular health?

Natto has also been studied in relation to cardiovascular health. Here, it is especially important to distinguish between eating natto as a food and taking a concentrated nattokinase supplement.

A large prospective study published in The BMJ followed 92,915 Japanese adults. Higher consumption of fermented soy foods, including natto and miso, was associated with lower overall mortality, while natto intake showed an inverse association with cardiovascular mortality.

The study was observational, which means it cannot establish cause and effect. The authors also noted that unmeasured or incompletely controlled factors may have contributed to the association.

The results therefore do not prove that natto prevents cardiovascular disease. They show an association that is interesting enough to justify further research.

Vitamin K2 and nattokinase are also studied separately for potential cardiovascular effects. Findings from these studies should not automatically be attributed to an ordinary serving of natto.

What is nattokinase, and is it the same as natto?

Nattokinase is an enzyme produced during natto fermentation. It was isolated from natto and has attracted scientific interest because of fibrinolytic activity observed in laboratory research.

Natto and nattokinase are not the same thing. Natto is a complete fermented food, whereas nattokinase is one component that can be isolated from it.

Natto	Nattokinase
Fermented food	Enzyme
Contains protein, fiber, minerals, and vitamin K2	Isolated compound
Eaten as food	Can be sold as a supplement
Contains many naturally occurring compounds	Supplements may provide concentrated doses

This distinction is important when interpreting research. Findings from a study using a concentrated nattokinase supplement cannot automatically be applied to natto as a food.

A meta-analysis of randomized trials of nattokinase supplements found modest reductions in systolic and diastolic blood pressure. It did not find consistent improvements in blood lipids, and the relatively small number of studies and participants means the results should be interpreted cautiously.

These results apply to nattokinase supplements rather than ordinary servings of natto. They do not demonstrate that eating natto produces the same cardiovascular effect.

Can natto support gut health?

Natto is fermented with Bacillus subtilis var. natto, which has led researchers to investigate its possible effects on the intestinal microbiota. Several small studies have reported changes in intestinal bacteria or bowel-movement frequency after natto consumption.

Human clinical evidence is still limited, however. A review of fermented foods found some indications that natto may influence the gastrointestinal microbiota and stool frequency, but there were too few controlled studies for firm conclusions.

It is therefore more accurate to say that the relationship between natto and gut health is promising and still being studied. Claims that natto “repairs the microbiome” or acts as a treatment for digestive disorders go beyond what the current evidence establishes.

How much natto can we eat and how is it served?

There is no official recommendation establishing an amount of natto that every adult should eat each day. In Japan, natto is commonly sold in individual containers and eaten as part of a meal.

A commercial serving is often around 40–50 g, although serving sizes vary between products. The 100 g values used in nutrition tables are mainly a standardized way to compare foods rather than a suggested serving size.

Natto can be eaten:

• with rice;
• with green onions;
• with Japanese mustard;
• with soy sauce;
• alongside vegetables;
• in a variety of Japanese dishes.

Before eating, natto is often stirred vigorously. This makes its characteristic long, sticky strings even more noticeable.

Its strong aroma, fermented flavor, and texture can take some getting used to for people trying it for the first time. There is no need to eat 100 g simply because nutrient values are often presented for that amount.

How is natto different from miso, tempeh, and other fermented soy foods?

Natto, miso, tempeh, and soy sauce are all made from soy or can contain soy, but their fermentation processes are different. Different microorganisms and production methods create different flavors, textures, and nutritional profiles.

Food	Fermentation	Main characteristic
Natto	Bacillus subtilis var. natto	Sticky texture, particularly rich in MK-7
Tempeh	Mainly Rhizopus fungi	Firm texture and milder flavor
Miso	Fermentation with koji and other microorganisms	Salty paste used for seasoning
Soy sauce	Complex fermentation	Liquid seasoning, usually high in sodium

The fact that all of these foods are fermented soy products does not mean they have the same properties. Fermentation organisms and processing methods strongly influence the final composition.

The particularly high concentration of MK-7 is one characteristic that distinguishes natto from many other fermented foods. This makes the foods nutritionally related but not interchangeable.

Who should be cautious with natto?

The most important precaution concerns people taking warfarin or other vitamin K antagonist medications. Warfarin works by interfering with the vitamin K cycle, so major changes in vitamin K intake can alter the effect of the medication.

Natto can provide particularly large amounts of vitamin K2. For this reason, someone taking warfarin should not begin eating natto regularly or make a major change in their usual natto intake without discussing it with the healthcare professional monitoring their treatment.

People with a soy allergy should also avoid natto because soybeans are its main ingredient. The same general allergy precautions that apply to other soy foods apply to natto.

Additional caution is appropriate with nattokinase supplements. Concentrated nattokinase should not be treated as equivalent to eating an ordinary fermented food, particularly for people using medications that affect blood clotting.

Written by Victoria, founder and editor of RoutineHealth. This article is for general education and is not medical advice. The information provided should not be used to diagnose, treat, or prevent a medical condition. If you take warfarin, another anticoagulant or vitamin K antagonist, have a soy allergy, have a medical condition, or are considering a nattokinase supplement, speak with a qualified doctor or pharmacist before making significant dietary changes or using a supplement. How we research and correct articles is explained in our Editorial Policy; see also our Medical Disclaimer.

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