What is Natto? Nutritional Benefits of a Japanese Superfood

What is natto? Natto is boiled soybeans that have been fermented with a starter culture for a short incubation period.

During this process, as the culture feeds on the bean substrate, it produces a wispy thread-like biofilm that has a rather slimy sticky texture. Hence natto's common name "sticky beans."

Its distinct flavor and gooey texture is an acquired taste and mouthfeel to many Westerners, however, natto has long been a popular everyday food in Japan and other parts of Asia for centuries.

There are many different regional styles of nattō (納豆) in Japan. Usually, most are made from small soybean varieties which provide a stringier "neba neba" texture.

Natto is Not a type of miso. Yes, soybeans are the main ingredient involved, but natto isn't salty like miso nor does it taste anything like it. The Bacillus subtilis natto culture species used to ferment the beans, grows in an alkaline environment not an acidic one like miso or other fermented foods. This accounts for its different earthy robust flavor.

There are many stories on the origins of natto, but all center around the discovery that when you pack boiled soybeans in a wrapping of rice straw, they eventually produce natto. Since Bacillus subtilis natto is found on the straw this was one of the initial ways used to inoculate the beans.

Now, DIY natto can be made from either a starter powder or a small amount of natto from another batch. When making it homemade style it can also be made with other types of legumes not just the soybean. Fermentation involves a consistent incubation temperature of about 105°F (40°C) for up to 24 hours.

Natto is rarely eaten by itself but served as either a condiment topping or as a main part of a meal.

The classic Japanese way to eat natto is over a bowl of rice, topped with scallions and sometimes a raw egg. But first, it is frequently stirred in a bowl in a circular motion with chopsticks with added seasonings like hot mustard, shoyu, seaweed flakes or other Japanese spices. The stirring part is to help break up the strands and produce a more uniform texture, merging any liquid with the biofilm coating.

Natto is common as a breakfast food or part of a "natto teishoku" or meal set in which other side dishes like soup, rice, fish, seaweed or pickled foods are served.

We personally enjoy natto, especially as a breakfast food atop cooked grains, porridge, eggs or tofu scrambler with a side of sauerkraut. It has a slight bitterness with a coffee-like taste and scent. Some also describe it to have an aged cheesy flavor.

If you'd like to eat natto for its health benefits not necessarily for its taste, it can be camouflaged easily into recipes like sauces and dressings or used in nori rolls. It goes well in low temp miso soup, but the important thing is not to heat natto or you will lose some of its nutritional benefits, especially the probiotic and enzyme content.

The goopy long cobweb-like strands that persist when the soybeans are pulled apart can literally stretch across a small room. (we've tried it!) They are a type of sticky mucilage and soluble fiber that is naturally created to give the B. subtilus natto culture a protective environment in which to multiply.

The main component of this slimy goo is a substance called polyglutamic acid, or more specifically poly-gamma-glutamic acid or Gamma PGA (γ-PGA). This compound is a naturally occurring biopolymer that consists of repeating units of l-glutamic acid, d-glutamic acid or both. (*)

Glutamic acid or glutamate is the amino acid known for its savory UMAMI flavor that can enhance the taste of other foods.  

While, yes, natto may not be for all palates or taste buds, it can be one worth trying for its nutritional paybacks.

Not only is natto a probiotic-rich food source to add to the diet, it is also famous for two health-promoting substances we will now discuss.

What is Natto Good For? Top 2 Nutrients

Natto is known for its high amounts of nattokinase. NATTOKINASE (pronounced nuh-TOH-kin-ayss) is a natto-specific enzyme produced by the B. subtilus spores and is especially concentrated in the biofilm strands.

Nattokinase has been proposed in research to offer beneficial support to the cardiovascular system because it’s shown to offer antihypertensive, antithrombotic, anti-atherosclerotic, anticoagulant and neuroprotective effects. It is especially known for its protective actions against blood clot formation.

The consumption of natto is reported to contribute to the longevity of the Japanese population due to its studied association with decreased risk of cardiovascular diseases.

Although natto is a whole-food form of this enzyme, nattokinase is also extracted from natto and sold as a popular dietary supplement marketed for cardiovascular and circulatory support.

Natto fermented soybeans and their nattokinase enzymes also aid in the production of a certain vitamin known as K2. What is vitamin K2 good for? Vitamin K2 works to ensure the body's proper utilization of the mineral calcium by supporting its uptake by the bones rather than depositing calcium in the soft tissues of the joints and arteries, influencing issues like arthritis and vascular calcification. 

Natto more specifically contains a distinct long-chain K2 variant called MK-7. Natto is considered the highest source of MK-7 of all foods. (*) Some reports in fact indicate that 100 grams (a little more than 1/2 cup) of natto can contain about 1000 micrograms of MK-7 or vitamin K2. 

Currently the FDA’s Daily Value for vitamin K (not vitamin K2 specifically) is 80 micrograms, based on an adult caloric intake of 2,000 calories.

The most common sources of K2 in the diet are animal foods like meat, liver, eggs and other dairy products. These foods are typically composed of short-chain K2 variant called MK-4. Vitamin K2 in the form of MK-7, unlike MK-4, is not only claimed to have a higher bioavailability but also goes directly into the bones as well as stays in the body longer than MK-4. 

Natto is a great K2 plant-based option for vegans and vegetarians or those who have trouble digesting aged cheeses, the other source of MK-7. As a fermented food, natto can be potentially more beneficial at increasing uptake of this important nutrient.

In conjunction with vitamin D3, vitamin K2 in the form of MK-7 is frequently found in many nutritional supplements for bone support. Quality formulas often include good ratios of vitamin K2 and D3 as well as food-based calcium, magnesium and silica, all of which work synergistically with K2 for their influence on healthy bones, teeth and collagen.

Although consuming soy-based foods may not be for everyone, fermented foods like tempeh, miso and natto are considered much healthier over all because fermentation can remove some of the antinutrients found in soybeans.

The other good news is that if you're someone trying to avoid soy altogether, natto can be made with other types of beans. This also happens to be the case for other soy-based favorites, like miso and tempeh, which we have firsthand experience making homemade with other types of legumes besides soy. (See our garbanzo bean miso and black-eyed tempeh recipes.)

We have yet to experiment with natto, but according to Natto Dad, he has successfully made natto with pinto, mung bean, garbanzo and black bean.