Natto is a traditional Japanese dish made from fermented soybeans. It’s characterized by a slimy, sticky, and stringy texture and has many nutritional benefits. It may promote stronger bones and a healthier heart.

Some research suggests that adding natto to your diet can offer numerous health benefits, such as supporting the immune system and improving digestion. More research is necessary to further support these claims.

This article explains what makes natto so nutritious and the possible benefits it may provide.

What is natto?

Natto is 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 (B. subtilis) on its surface. This allowed the bacteria to ferment the sugars present in the beans, eventually producing natto.

However, at the beginning of the 20th century, the presence of 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.

Natto is super nutritious. It contains good levels of many nutrients that are important for optimal health. A 3.5-ounce (100 grams) portion provides the following:

  • Calories: 211 kcal
  • Fat: 11 grams (g)
  • Carbs: 12.7 g
  • Fiber: 5.4 g
  • Protein: 19.4 g
  • Manganese: 1.53 milligrams (mg)
  • Iron: 8.6 mg
  • Copper: 0.667 mg
  • Vitamin K: 23.1 micrograms (mcg)
  • Magnesium: 115 mg
  • Calcium: 217 mg
  • Vitamin C: 13 mg
  • Potassium: 729 mg
  • Zinc: 3.03 mg
  • Selenium: 8.8 mcg

Natto also contains smaller amounts of vitamin B6, folate, pantothenic acid, as well as antioxidants and other beneficial plant compounds.

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.

Natto improves your digestion

Having the right type of bacteria in your gut creates a healthy gut flora, which is linked to numerous health benefits, such as improved digestion.

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 symptoms such as bloating and constipation.

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.

Natto fermentation helps reduce the levels of antinutrients that are naturally found in soybeans, facilitating their digestion.

Natto is rich in several nutrients that contribute to healthy bones.

A 3.5-ounce (100 g) portion of natto provides 217 mg of calcium, the main mineral found in your bones. The recommended daily allowance (RDA) of calcium for adults is between 1,000 mg and 1,300 mg.

Natto may contribute to a healthier heart. — partly because it contains fiber, which can help reduce cholesterol levels.

Furthermore, natto fermentation produces nattokinase, a type of enzyme that helps dissolve blood clots.

Talk with your doctor if you wish to find out about supplements that may improve your heart health.

Natto may strengthen your immune system

Natto contains several nutrients that may help strengthen your immune system.

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.

Moreover, probiotics further reduce the risk of infection and may help you recover faster if you do get sick.

In a 2015 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 less likely to experience a respiratory infection over the 4-month study period.

In addition to its probiotic content, natto contains vitamin C, iron, zinc, selenium, and copper — all of which play important roles in immune function.

Other potential benefits

Regularly eating natto may provide several other benefits:

  • Natto may reduce the risk of cancer: Natto contains soy isoflavones and vitamin K2, both of which may be linked to a lower risk of cancer. However, more research is necessary.
  • Natto may help you lose weight: Natto contains good amounts of probiotics and fiber, both of which may help prevent weight gain and optimize weight loss.

Overall, more studies are necessary before strong conclusions can be made.

Should you eat natto?

Natto consumption is generally safe for most people.

However, natto contains vitamin K1, which plays a role in blood clotting. 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.

How to make homemade natto

You can find natto in most Asian supermarkets, but you can also make it at home.

Ingredients

  • 1.5 lb (0.7 kg) of soybeans
  • water
  • natto starter or a package of store-bought natto

Supplies

  • a large cooking pot
  • a sterilized, oven-safe dish with a lid
  • a kitchen thermometer
  • a pressure cooker (optional)

To make

  1. Thoroughly wash the soybeans under running water and place them in a pot.
  2. Pour fresh water over the beans so they’re fully submerged. Let soak for 9 to 12 hours, or overnight. Use approximately 3 parts water to 1 part soybeans.
  3. Drain the beans, add fresh water, and boil them for approximately 9 hours. Alternatively, you can use a pressure cooker to reduce the cooking time to around 45 minutes.
  4. 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.
  5. Follow the package instructions for adding the natto starter to the beans. You can also use store-bought natto and mix it in with the boiled beans.
  6. Stir everything together using a sterilized spoon, making sure all beans come into contact with the starter mix.
  7. Cover the dish and place it in the oven to ferment for 22 to 24 hours at 100°F (37.8°C).
  8. 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 to 96 hours, but those who are anxious to try their natto may do so after about 3 hours of aging.

Any leftovers can be stored in the freezer for later use.

The bottom line

Natto is a nutritious food. Eating it regularly may help 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.

If you’d like more information about natto’s possible health benefits, speak with your doctor or a registered dietitian.