While few people in the Western world have heard of natto, it’s very popular in Japan.
This fermented food has a unique consistency and surprising smell. In fact, many say it’s an acquired taste. However, you shouldn’t be deterred by this.
Natto is incredibly nutritious and linked to various health benefits, which range from stronger bones to a healthier heart and immune system.
This article explains what makes natto so nutritious and why you should consider giving it a try.
What Is Natto?
Natto is a traditional Japanese dish consisting of fermented soybeans and characterized by a slimy, sticky and stringy texture.
It’s easily recognizable by its distinctive, somewhat pungent smell, while its flavor is commonly described as nutty.
In Japan, natto is typically topped with soy sauce, mustard, chives or other seasonings and served with cooked rice.
Traditionally, natto was made by wrapping boiled soybeans in rice straw, which naturally contains the bacteria Bacillus subtilis on its surface.
Doing so allowed the bacteria to ferment the sugars present in the beans, eventually producing natto.
However, at the beginning of the 20th century, the B. subtilis bacteria was identified and isolated by scientists, which modernized this preparation method.
Nowadays, the rice straw has been replaced with styrofoam boxes in which B. subtilis can be directly added to boiled soybeans to start the fermentation process.
Summary: Natto is a traditional Japanese dish made from fermented soybeans. It has a sticky texture, pungent odor and somewhat nutty flavor.
It Is Rich in Several Nutrients
Natto is super nutritious. It contains good levels of many nutrients that are important for optimal health. A 3.5-ounce (100-gram) portion provides the following (1):
- Calories: 212
- Fat: 11 grams
- Carbs: 14 grams
- Fiber: 5 grams
- Protein: 18 grams
- Manganese: 76% of the RDI
- Iron: 48% of the RDI
- Copper: 33% of the RDI
- Vitamin K: 29% of the RDI
- Magnesium: 29% of the RDI
- Calcium: 22% of the RDI
- Vitamin C: 22% of the RDI
- Potassium: 21% of the RDI
- Zinc: 20% of the RDI
- Selenium: 13% of the RDI
Natto also contains smaller amounts of vitamin B6, folate and pantothenic acid, as well as antioxidants and other beneficial plant compounds (2).
Natto is especially nutritious because its soybeans undergo a process of fermentation, which creates conditions that promote the growth of probiotics.
Probiotics are beneficial bacteria that provide a wide range of health benefits. One such benefit includes making foods more digestible, which makes it easier for your gut to absorb their nutrients (3, 4, 5).
This is one reason why natto is considered more nutritious than boiled soybeans.
Summary: Natto is rich in protein, vitamins and minerals. The fermentation process it undergoes reduces its antinutrients, increases its beneficial plant compounds and helps your body absorb the nutrients that it contains.
Natto Improves Your Digestion
Your gut contains trillions of microorganisms — more than 10 times the total number of cells found in your body.
The probiotics in natto can act as your gut’s first line of defense against toxins and harmful bacteria.
Researchers report that probiotics can help reduce gas, constipation, antibiotic-associated diarrhea and bloating, in addition to symptoms of inflammatory bowel disease (IBD), Crohn’s disease and ulcerative colitis (12, 13, 14).
Most probiotic-rich foods and supplements contain 5–10 billion colony-forming units (CFUs) per serving. Comparatively, natto can contain between one million and one billion colony-forming bacteria (CFUs) per gram (15).
Thus, each gram of natto contains almost the same amount of probiotics you’d get from a whole serving of most other probiotic-rich foods or supplements.
In addition, soybeans naturally contain antinutrients, which can make it more difficult for your body to digest them. Antinutrients can also reduce the amount of nutrients your body absorbs from foods and may cause bloating or nausea in some people.
Summary: Natto contains fewer antinutrients and more probiotics than non-fermented soybeans. This reduces unpleasant digestive symptoms and helps your body absorb nutrients more easily.
It Contributes to Stronger Bones
Natto is rich in several nutrients that contribute to healthy bones.
To start, a 3.5-ounce (100-gram) portion of natto provides 22% of the recommended daily intake (RDI) of calcium, the main mineral found in your bones (1).
In addition, natto is one of the rare plant sources of vitamin K2.
It should not be confused with vitamin K1, which plays an important role in blood clotting. For reference, natto contains both vitamins K1 and K2 (20).
Nonetheless, some of the studies on vitamin K2 and bone health used very high supplement dosages. While eating natto can raise your vitamin K2 levels, it’s not yet known whether eating natto alone would provide the same level of benefits (24).
Summary: Natto contains calcium and vitamin K2, both of which contribute to stronger, healthier bones.
It Promotes Heart Health
Natto may also contribute to a healthier heart.
Moreover, Japanese researchers report that natto may help lower blood pressure by inactivating angiotensin converting enzyme (ACE), which helps control blood pressure.
Finally, in addition to strengthening your bones, the vitamin K2 in natto helps prevent calcium deposits from accumulating in your arteries (33).
In one study, regular intake of vitamin K2-rich foods was linked to a 57% lower risk of dying from heart disease (34).
In another study including only women, every 10 mcg of vitamin K2 consumed per day was linked to a 9% reduction in heart disease risk (35).
For reference, natto is estimated to contain around 1 gram of vitamin K2 per 3.5-ounce (100-gram) serving (36).
Summary: Natto contains fiber, probiotics, vitamin K2 and nattokinase. This combination may help reduce cholesterol and blood pressure levels and decrease the risk of heart disease.
Natto May Strengthen Your Immune System
Natto contains several nutrients that may help strengthen your immune system.
To begin with, probiotic-rich foods such as natto contribute to a healthy gut flora. In turn, a healthy gut flora helps prevent the growth of harmful bacteria and may even boost your production of natural antibodies (37, 38, 39, 40).
In one study, elderly people were provided 2 billion CFU of B. subtilis — the probiotic strain found in natto — or a placebo. Those given the probiotic strain were 55% less likely to suffer from a respiratory infection over the four-month study period (43).
What’s more, a probiotic-rich diet may also reduce the likelihood of needing antibiotics to recover from an infection by around 33% (44).
Summary: Natto is rich in probiotics, vitamin C and several minerals, all of which contribute to a healthy immune system.
Other Potential Benefits
Regularly eating natto may provide several other benefits:
- May reduce the risk of certain cancers: Natto contains soy isoflavones and vitamin K2, both of which may be linked to a lower risk of liver, prostate, digestive and breast cancer (47, 48, 49, 50, 51).
- May help you lose weight: Natto contains good amounts of probiotics and fiber, both of which may play a role in preventing weight gain and optimizing weight loss (52, 53, 54).
- May improve brain health: Probiotic-rich foods such as natto may help reduce stress, improve memory, and reduce symptoms of anxiety, depression, autism and obsessive-compulsive disorder (OCD) (55, 56, 57, 58).
That said, it’s important to note that the amount of studies directly linking natto to these benefits remains small.
Overall, more studies are needed before strong conclusions can be made.
Summary: Natto may benefit weight loss, brain health and offer protection against certain types of cancer. However, more research is needed.
Should You Eat Natto?
Natto consumption is generally safe for most people.
Nevertheless, natto contains vitamin K1, which has blood-thinning properties. For this reason, individuals already taking blood-thinning medication should seek advice from their doctor before adding natto to their diets.
In addition, natto is made from soybeans, which are considered a goitrogen.
This means it may interfere with the normal functioning of the thyroid gland, especially in individuals with an already poorly functioning thyroid.
This is unlikely to pose a problem for healthy individuals. However, those with impaired thyroid function may want to limit their intake.
Summary: Natto is safe for most people to eat, though individuals on blood-thinning medication or with thyroid problems should consult their doctor before adding natto to their diet.
How to Make Homemade Natto
Natto can be found in most Asian supermarkets, but it can also be made at home.
Here are the ingredients you’ll need:
- 1.5 pounds (0.7 kg) of soybeans
- Natto starter or a package of store-bought natto
- A large cooking pot
- A sterilized, oven-safe dish with a lid
- A kitchen thermometer
- A pressure cooker (optional)
Here are the steps to follow:
- Thoroughly wash the soybeans under running water and place them in a pot.
- Pour fresh water over the beans so they are fully submerged and let them soak for 9–12 hours, or overnight. Use approximately 3 parts water to 1 part soybeans.
- Drain the beans, add fresh water and boil them for approximately 9 hours. Alternatively, use a pressure cooker to reduce cooking time to around 45 minutes.
- Drain the cooked beans and place them in a sterilized, oven-safe dish. You can sterilize the dish by boiling water in it for at least 10 minutes before use.
- Add the natto starter to the beans, following the package instructions. You can also use store-bought natto and simply mix it in with the boiled beans.
- Stir everything together using a sterilized spoon, making sure all beans come into contact with the starter mix.
- Cover the dish and place it in the oven to ferment for 22–24 hours at 100°F (37.8°C).
- Cool the natto for a couple of hours and allow it to age in your refrigerator for approximately 24 hours before eating.
Natto is generally aged in the refrigerator for 24–96 hours, but those who are anxious to try their natto may do so after about three hours of aging.
Any leftovers can be stored in the freezer for later use.
Summary: Follow the steps above to make your own homemade natto. You can also find it in most Asian supermarkets.
The Bottom Line
Natto is an incredibly nutritious food that’s worth acquiring a taste for.
Eating it regularly may strengthen your immune system and bones, protect you from heart disease and help you digest foods more easily.
If you’re planning to taste natto for the first time, start with a small portion, adding plenty of condiments and working your way up gradually.