Natto: The Fermented Soy Superfood

October 24, 2023

There’s a lot of controversy around soy and soy-based products like natto. With all the contradictory claims out there from researchers and health experts alike, it’s no wonder that many people are left scratching their heads on whether soy helps or harms your health.

The answer is: It depends. Marketing geniuses have posited soy as the wonder health alternative to virtually everything. In most supermarkets, you’ll find soy milk, soy protein, soybean oil, soy lecithin and even soy soap.

Unfortunately, though, many forms of soy are not necessarily as healthy as food manufacturers would like you to believe.

The problem is the soy you see in all these foods is not the traditionally grown crop of Japan. In fact, the majority of soy that you find in in grocery stores is actually genetically modified (GMO), produced in a different way and doesn’t yield the same nutritional benefits.

However, when you ferment soybeans you have a completely different product that boasts an entirely separate set of nutrients, which is why when it comes to soy, the safest and best way to consume it is through fermented foods like miso, tempeh or natto.

So what is natto, and how can it impact your health? Let’s dig in.

What Is Natto?

Natto is a traditional food usually consumed at Japanese breakfast tables together with miso soup, fish and rice.

Tofu, tempeh, miso and natto are all whole food forms of soybean. However, unlike many other soy foods, natto is fermented, which accounts for many of its health-promoting properties.

It is made by soaking whole soybeans, then steaming or boiling them, and afterward adding the bacteria Bacillus subtilis to the mixture. It is then allowed to ferment over time.

Natto is known to be a rather acquired taste, probably due to its unique smell and texture. What does natto taste like? It has a distinct, bitter flavor, and for many people, the ammonia smell may evoke a mixture of old socks and cheese.

As for the texture, it resembles a gooey, stringy and sticky small bean, which also adds to its unappealing nature.

People typically have strong feelings toward natto — they tend to either love it, hate it or eat it until it grows on them. The taste of natto is actually not that bad — it’s the unpleasant smell and stringy texture that can be surprising and unfamiliar to most western taste buds and palates.

If you can tolerate it, however, it’s packed with powerful nutrients that can make a serious impact on your overall health.

Although its true origins remains a mystery, there are many different theories about the creation of the natto food product. Some say that it was discovered when the Japanese samurai clan Minamoto no Yoshiie was attacked while boiling soybeans to feed their horses. They quickly packed the soybeans into straw bags and did not open them until several days later, at which point the soybeans had fermented to form natto.

Meanwhile, others believe that it was developed in several different locations around Japan as the ingredients have all been widely available since ancient times.

In the early 1900s, researchers discovered that the starter culture used to make natto could be produced without the use of straw. This changed the way that it was produced and made it much easier for food manufacturers to begin commercial production of natto, increasing its popularity and making it possible to enjoy all around the globe.

Nutrition Facts

While natto’s appearance may not leave a very good first impression, its nutrition profile makes it well worth giving it a chance. It is as an excellent source of protein, fiber, vitamins and minerals. Additionally, the Bacillus subtilis in natto creates an enzyme called nattokinase, which aids in the production of vitamin K2 and helps preserve heart health.

Rich in macronutrients and micronutrients, natto is fantastically nutritious, which is why people who regularly consume it experience a wide array of health benefits. It’s the very definition of a “superfood” and contains huge amounts of beneficial nutrients in every serving.

A one-cup serving of natto (about 175 grams) contains approximately:

Calories: 369
Total Carbohydrates: 22.2 g
- Fiber: 9.5 g
- Sugar: 8.6 g
Total Fat: 19.2 g
- Saturated Fat: 2.8 g
- Polyunsaturated Fat: 10.9 g
- Monounsaturated Fat: 4.3 g
- Trans Fat: 0 g
Protein: 34 g
Sodium: 12.2 mg (0.5% DV*)
Copper: 1.2 mg (133% DV)
Manganese: 2.7 mg (117% DV)
Iron: 15 mg (83% DV)
Magnesium: 201 mg (48% DV)
Zinc: 5.3 mg (48% DV)
Vitamin K: 40.4 mcg (34% DV)
Calcium: 380 mg (29% DV)
Selenium: 15.4 mcg (28% DV)
Potassium: 1,280 mg (27% DV)
Vitamin C: 22.8 mg (25% DV)
Thiamine: 0.3 mg (25% DV)
Riboflavin: 0.3 mg (23% DV)
Vitamin B6: 0.2 mg (12% DV)

*Daily Value: Percentages are based on a diet of 2,000 calories a day.

In addition to the nutrients listed above, natto also contains a small amount of folate, pantothenic acid and sodium as well.

Vs. Nattokinase

Nattokinase is an enzyme that is isolated from natto and credited with supplying many of its potent health benefits. In particular, nattokinase has been shown to help prevent blood clots, promote blood flow and improve heart health.

It’s also been shown to be useful in the treatment of conditions like high blood pressure, stroke, atherosclerosis and Alzheimer’s disease.

Although plenty of other fermented soy foods boast a long list of health benefits, natto is the only soy product that contains nattokinase. Additionally, while nattokinase is also available in supplement form to help you get in your daily dose, adding natto to your diet instead can provide a burst of added nutrients and probiotics as well as a hearty chunk of nattokinase in each and every serving.

Health Benefits

1. Rich in Vitamin K

One of the main reasons that natto is so good for you is because it is rich in vitamin K. In fact, the Department of Public Health reports that it contains 100 times more vitamin K2 than cheese!

Vitamin K2 is important because, according to the National Institutes of Health, it’s considered a key component in maintaining the bone mineral density of postmenopausal women suffering from osteoporosis. This is especially good news for vegetarians and vegans because natto is one of the few plant-based sources of vitamin K2.

Having a higher intake of vitamin K2 is associated with lower risk of heart disease, artery calcification and death. Vitamin K2 also supports bone health by increasing bone mass and slowing bone loss that occurs over time.

2. Contains Nattokinase

During the fermentation process, soy becomes more easily digested and absorbed, which is especially good news for those who normally suffer gut issues when eating legumes. One reason natto doesn’t trigger gastrointestinal discomfort like other forms of soy is because of the enzyme nattokinase.

Created during the fermentation process, nattokinase is used for a variety of medicinal purposes, including:

3. Packed with Probiotics

Another key to natto’s health benefits is its rich content of probiotics. Bacillus subtilis (also referred to as Bacillus uniflagellatus, Bacillus globigii and Bacillus natto) is the bacteria added to soybeans that is then left to ferment in order to create natto. It helps synthesize enzymes, which are used to reduce blood clotting, and produces vitamin K and B vitamins.

At one point in its history, it was even used as a broad-spectrum antibiotic.

Research reveals that supplemental Bacillus subtilis improves symptoms of irritable bowel syndrome, supports a healthy microbiome and helps protect against inflammation. In general, though, the major benefit of fermented foods like natto is that they support overall health and immunity to reduce your risk of disease and keep your body in tip-top shape.

4. Promotes Bone Health

Natto is loaded with several important micronutrients that play an important part in bone health. Calcium, for example, is one of the main structural components of bone tissue and absolutely essential to preventing bone loss throughout the life span.

Vitamin K is also crucial to bone health, with studies showing that a deficiency of this key vitamin can increase the risk of bone abnormalities like osteoporosis and fractures. Manganese, zinc and copper are just a few other minerals that are plentiful in natto and important when it comes to maintaining bone density.

In addition, a 2020 study published in the Journal of Nutrition found that “natto intake is inversely associated with osteoporotic fracture risk in postmenopausal Japanese women.” Meanwhile, a 2021 systematic review and meta-analysis concluded that “the dietary intake of natto demonstrated an improving effects on the [bone mineral density] of the femoral neck.”

5. Enhances Digestive Health

Filling up on probiotic foods like natto can help balance the bacteria in your gut to optimize the health of your digestive system. Research shows that disruptions in this delicate gut microbiome can have serious consequences ranging from digestive issues to increased allergy severity and beyond.

Getting plenty of probiotics from food or supplement sources has been shown to be beneficial in the treatment of diarrhea, ulcerative colitis and irritable bowel syndrome, among other issues.

6. Keeps Your Heart Healthy

Topping the charts as one of the most nutrient-dense foods on the planet, it should come as no surprise that squeezing a serving or two of natto into your diet can have a big impact on the health of your heart.

With over nine grams of fiber packed into each cup, it may help lower cholesterol levels to prevent plaque buildup in the arteries. It’s also high in vitamin K2, which has been linked to a reduced risk of arterial calcification and coronary heart disease.

Plus, studies even show that consumption of nattokinase, the main enzyme found in natto, has been associated with lower blood pressure and decreased blood clotting. Keeping your blood pressure under control can help ease the stress on your arteries and keep your heart muscle healthy and strong.

Soy Products

Although natto can be made with black beans, adzuki beans, kidney beans and even sunflower seeds, the bacteria used to make it thrives best on soybeans, which help produce nattokinase more efficiently. It is important to note that nattokinase is not found in other non-fermented soy foods, which makes the distinction between natto and unfermented, genetically modified soy very clear.

With that said, while fermented soybeans are a packed powerhouse of goodness, other soy products are packed powerhouses of health risks. For the most part, unfermented soy is full of:

Phytates — known to contribute to micronutrient deficiencies, such iron, zinc and calcium
Trypsin inhibitors — disrupt healthy digestion and can cause pancreatic disorders
Goitrogens — thyroid hormone blockers that may be tied to impaired thyroid function
Phytoestrogens — compounds that alter normal estrogen production and may be linked to breast cancer
Aluminum — known to contribute to Alzheimer’s disease and dementia
Genetically modified ingredients — more than 90 percent of soybeans grown in the U.S. are genetically modified

Unfortunately when it comes to GMOs, long-term health risks are still unknown. There are reports that genetically modified soybeans may impact formation of life-threatening food allergies, cause liver damage, disrupt fertility and alter fetal/childhood development.

One human study on consumption of genetically modified soybeans found that the modified genes for herbicide resistance actually transferred into the digestive tracts of participants and continued to function after the beans were digested. On the other hand, though, some reports find that animal testing on GMOs in food only occasionally reveal dangers to health.

Regardless, when eating soy, it’s best to stick to fermented varieties like natto, tempeh and miso. Not only do these probiotic foods contain a lower amount of antinutrients and other harmful compounds, but they are also higher in beneficial bacteria for your gut and contain a long list of potential health benefits.

How to Use

Wondering where to buy natto and how you can add it to your diet? Thanks to its growing popularity, it is now available at many natural food stores and specialty shops. You can also buy it online to have it delivered directly to your door.

Once you get your hands on this powerful superfood, there are plenty of ways to take advantage of the unique natto taste and nutrient profile. Try making a traditional Japanese natto breakfast by combining it with rice and pickled veggies.

Alternatively, you can make a natto roll using your favorite sushi ingredients to give the nutritional profile of your roll a major upgrade. It also works well with miso soup, fish and whatever vegetables you have on hand.

How to Make

Natto can easily be purchased and added to your favorite recipes and dishes. However, if you’re feeling up to the challenge, you can also try making it on your own at home.

Most recipes involve washing and soaking the soybeans for nine to 12 hours, draining them and then boiling for an additional nine hours. The soybeans should then be combined with a natto spore solution and placed into thin layers separated by a cheesecloth.

In a closed container, the natto should then be placed in a dehydrator or oven set to 100 degrees Fahrenheit and allowed to ferment for 22–24 hours. Once the final product is ready, it can be stored in the refrigerator or freezer to extend its shelf life even longer.

Risks and Side Effects

For most people, natto can be safely consumed with minimal risk of side effects. However, more research is still needed on the effects of nattokinase in supplement form as the potential long-term side effects of this supplement still remain unclear.

Because natto contains a specific type of vitamin K2, known as MK-7, it might interfere with blood-thinning drugs like warfarin when consumed in high amounts. For this reason, you should check with your doctor before adding this fermented soy to your diet if you’re currently taking any blood thinners.

Additionally, natto is relatively high in calories. It’s also loaded with protein, which can contribute to a slew of health conditions like kidney stones and bone loss when consumed in excess. For this reason, it’s important to keep your intake in moderation and pair it with other nutritious whole foods to avoid unintentional weight gain and other adverse side effects.

When it is all said and done, however, the positive health benefits far outweigh any risks associated with eating natto. Just keep things balanced, incorporate a wide variety of other foods into your diet, and swap it in for genetically modified and unfermented soy products in your diet.

Final Thoughts

What is natto? Produced from boiled soybeans that have undergone fermentation, it is a Japanese staple that is chock-full of powerful health benefits.
A few of the most impressive natto benefits include improvements in bone health, digestion and heart health. It is also high in protein, fiber and probiotics, as well as important micronutrients like manganese, iron, copper and vitamin K.
Natto stands out from other soy products because it is fermented, which increases its digestibility and helps your body absorb it better. It also contains nattokinase, a key enzyme that protects against blood clots and comes with a long list of health benefits.
For best results, try adding natto to your favorite rice and veggie dishes to squeeze more nutrients into your day and enjoy the multitude of health benefits that it has to offer.