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.
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
Natto also contains smaller amounts of vitamin B6, folate and 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.
This is one reason why natto is considered more nutritious than boiled soybeans.
Natto also contains fewer antinutrients and more beneficial plant compounds and enzymes than non-fermented soybeans
Your gut contains trillions of microorganisms — more than 10 times the total number of cells found in your body.
Having the right type of bacteria in your gut creates a healthy gut flora, which is linked to numerous health benefits like 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 gas, constipation, antibiotic-associated diarrhea and bloating, in addition to symptoms of inflammatory bowel disease (IBD), Crohn’s disease and ulcerative colitis.
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.
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.
Interestingly, 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.
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.
In addition, natto is one of the rare plant sources of vitamin K2.
Vitamin K2 plays an essential role in bone health by activating bone-building proteins that help bring calcium into your bones and keep it there.
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.
Studies show vitamin K2 supplements can slow age-related loss in bone mineral density and may reduce the risk of certain types of fractures by 60–81%.
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.
Natto may also contribute to a healthier heart.
That’s partly because it contains fiber and probiotics, both of which can help reduce cholesterol levels.
Furthermore, natto fermentation produces nattokinase, a type of enzyme that helps dissolve blood clots. It seems to be especially concentrated in the “stringy portion” of natto.
Moreover, Japanese researchers report that natto may help lower blood pressure by inactivating angiotensin converting enzyme (ACE), which helps control blood pressure.
In fact, several studies show that nattokinase supplements reduced blood pressure by around 3–5.5 mmHg in participants with initial blood pressure values of 130/90 mmHg or higher.
Finally, in addition to strengthening your bones, the vitamin K2 in natto helps prevent calcium deposits from accumulating in your arterie.
In one study, regular intake of vitamin K2-rich foods was linked to a 57% lower risk of dying from heart disease.
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.
For reference, natto is estimated to contain around 1 gram of vitamin K2 per 3.5-ounce (100-gram) serving.
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.
Moreover, probiotics further reduce the risk of infection and may help you recover faster if you do get sick.
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.
What’s more, a probiotic-rich diet may also reduce the likelihood of needing antibiotics to recover from an infection by around 33%.
In addition to its high probiotic content, natto is rich in vitamin C, iron, zinc, selenium and copper, all of which play important roles in immune function.
Regularly eating natto may provide several other benefits:
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.