Natto: The Fermented Soy Superfood

July 19, 2017

One of the most commonly asked food topics that I field from my readers is about soy, and is it good for you?

The answer is: sometimes. Marketing geniuses have poised soy as the wonder health alternative to virtually everything. In most supermarkets today you’ll find soy milk, soy protein, soybean oil, and even soy soap, but the soy in its many forms is not necessarily the health choice that it has been marketed to be.

The problem is that the soy that you are seeing in all these foods is not the traditionally grown crop of Japan. The majority of soy that you find in in grocery stores is actually genetically modified or GMO, and is not farmed the same way or yielding the same nutrition.

However, when you ferment soybeans you have a completely different product that yields a completely different nutrient system for the body. When it comes to soy, the safest (and in my opinion the only) way to consume it is through fermented soy products like miso, tempeh or natto.

So What is Natto?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.  The key to natto’s health benefits is that it is fermented. Natto is made by soaking whole soybeans, then steaming or boiling them, and afterwards adding the bacteria Bacillus subtilis to the mixture.  It is then allowed to ferment over time. (1)

Natto is known to be a rather acquired taste, probably due to its smell and texture; and for many people the ammonia smell may evoke a mixture of old socks and cheese. As for the texture, it’s resembles a gooey, stringy and sticky small bean, which also adds to its unappealing nature.

People have strong feelings towards natto – they tend to either love it, hate it, or eat it until it grows on them. Actually, the taste of natto is not that bad, it’s the unpleasant smell and stringy texture which can be surprising and it is simply not a texture that our western taste buds and palate are used to.

Natto Nutrition Facts

While natto’s appearance may not leave a very good first impression, its nutrition is well worth giving it a chance.  Natto is as an excellent source of protein, fiber, vitamins and minerals. (2) Additionally, the Bacillus subtilis in natto creates an enzyme called nattokinase, which produces vitamin K2 (more on that later).

Rich in macronutrients and micronutrients, natto is fantastically nutritious, which is why people who regularly consume natto experience a fantastic array of health benefits. The nutritional profile of just one cup of natto include: (3)

  • Protein: 31.0 g
  • Manganese: 134%
  • Iron: 84%
  • Copper: 58%
  • Magnesium: 50%
  • Calcium: 38%Potassium: 36%
  • Zinc: 35%
  • Phosphorus: 30%
  • Selenium 22%

A whopping 38% of the daily recommended amount of calcium! It’s interesting to compare it to milk which only provides 29% of the daily recommended amount of calcium), and is very high in iron, potassium, copper, zinc, phosphorus, magnesium, manganese and selenium. It’s also very low in sodium. (4)

In terms of vitamins, one cup of natto provides the following (in daily recommended values):

  • Vitamin K: 51%
  • Vitamin C: 38%
  • Riboflavin: 20%
  • Thiamin: 19%
  • Vitamin B6: 11%
  • Folate: 4%
  • Pantothenic Acid: 4%
Natto Nutrition

Why is Natto so Nutritious?

1. Loaded with Vitamin K Benefits

One of the main reasons natto is so good for you is because it is rich in vitamin K. In fact, the Department of Public Health reports that Natto contains 100 times more vitamin K2 than cheese! (5) The importance of K2 is profound because, according to the National Institutes of Health, it is a key component in maintaining the bone mineral density of postmenopausal women suffering from osteoporosis. (6) As described by the George Mateljan Foundation:

“There are three basic types of vitamin K. Their common names are K1, K2, and K3. The K1 form of vitamin K is found in plant foods, and many of our best sources of this vitamin are green vegetables (including 16 excellent sources); this makes good sense since K1 is required for green plants to conduct the process of photosynthesis. The K2 form of vitamin K is made from K1 and K3 by bacteria and other microorganisms. It can also be made in the human body through a conversion process involving K1 and K3.” (7)

This is especially good news for vegetarians and vegans because vitamin K2 is generally obtained by eating meat and other animal products. (8)


The first key vitamin K2 benefit is heart health. (9). K2 has been shown to help prevent hardening of your arteries, which is prevalent in coronary heart disease and heart failure. Dr. Weston Price observed that it may even reverse arterial calcification. (9, 10) Also known to prevents age-related neurological degeneration, vitamin K2 helps prevent kidney stones. (11)

Also, because it is fermented, natto has a completely different nutritional makeup from raw soy beans; especially the genetically modified variety! On one hand, when natto is fermented the soybean loses vitamin A, several other vitamins and minerals, and decreases in calorie content and sodium. But what it gains from the process more than makes up for these nutrition losses. Natto is a superior source of nutrients. (12)

2. Fermentation Benefits

Due to fermentation, soybean proteins are 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 soy traditionally does is because of the enzyme nattokinase. Created during the fermentation process, nattokinase is used for a variety of medicinal purposes: (13)

  • Beriberi (B vitamin deficiency)
  • Cancer
  • Chronic fatigue syndrome
  • Endometriosis
  • Fibromyalgia
  • Infertility
  • Pain
  • Muscle spasms
  • Uterine fibroids

3. Probiotics Benefits

Another key to natto’s health benefits is its rich probiotics content. Bacillus subtilis, (also referred to as Bacillus uniflagellatus, Bacillus globigii, and Bacillus natto), is the bacteria added to soybeans and then left to ferment in order to create natto. It’s key function is that it produces enzymes, which are used to reduce blood clotting and produces vitamin K and B vitamins. (14) At one point in its history, it was even used as a broad spectrum antibiotic!

Highlighted Colon

Research conducted by the National Center for Biotechnology Information reveals that supplemental Bacillus subtilis improves symptoms of irritable bowel syndrome. (15) It is also used for:

  • Treating gastrointestinal conditions.
  • Prevent allergic disorders.
  • Fight cancer.
  • Increasing immune reaction of intestinal cells.

Subsequently, when natto is eaten on a regular basis, these are some of the more common health benefits you can expect: (16)

  • Effective against high cholesterol.
  • Effective against osteoporosis and hip fractures.
  • Fights against fibromyalgia.
  • Lowers blood pressure and improves circulation.
  • Less risk of colon cancer.
  • Less risk of breast cancer (as soy appears to lengthen the menstrual cycle).
  • Prevents stroke, heart attack and heart disease.
  • Prevents vitamin-deficiency disease.
  • Reduces the symptoms associated with menopause.
  • Relieves constipation.

Natto vs. GMO Soy

Although natto can be made with black beans, adzuki beans, kidney beans and even sunflower seeds, the Bacillus subtilis thrives best on soybeans; which helps to 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: (17)

  • Phytates – known to cause tooth decay and stunts growth.
  • Trypsin inhibitors – which disrupt healthy digestion and can cause pancreas disorders.
  • Goitrogens – thyroid hormone blockers that can cause cancer and hypothyroidism.
  • Phytoestrogens – compounds that block normal estrogen production that are linked to breast cancer.
  • Hemagglutinin – blot clotting agents that can cause hypoxia (low oxygen levels)
  • Aluminum – known to cause Alzheimer’s disease and dementia
  • Vitamin B12 inhibitors– can contribute to vitamin B12 deficiency.
  • GMO – more than 90% of soy grown in the U.S. is genetically modified.
No Gmo

This last point about genetically modified organisms (GMO) cannot be overemphasized because of the undeniable role that they play in:

  • Allergies
  • Antibiotic resistance
  • Cancer
  • Endocrine system disruption
  • Premature aging
  • Reproductive system disorders

The Institute for Responsible Technology takes it one step further and reports that genetically modified food has more than 65 health risks, which includes everything from intestinal damage to death. (18) Yet, at this point, no one really knows what GMOs will mean for our health. They’ve only been on the market for 30 years and no long-term studies have been conducted over the span of a person’s lifetime. Truth is, people eating GMOs are the science experiment and we can only wait and see how detrimental they really are.

Natto Possible Side Effects

Various sources warn that the nattokinase in natto is safe when eaten in the amount from food, but it is better to be cautious of it in supplement form, as more research is necessary to prove its safety and interaction with other elements. (18)

fermented soy beans

Also, at 371 calories per cup, the average adult on a 2,000-calorie diet would take in nearly 20% of their daily energy intake in just one sitting! The Japanese aren’t traditionally known as being a culture that struggles with obesity because of their active lifestyle and wholesome diet, but Americans are.

Meaning this, if you eat a typical American diet and add a couple cups of natto to your regimen because you think it’s healthy for you, you very well may be putting yourself at risk of gaining weight!

Same thing with protein. The average male should eat 70% of his body weight in grams of protein. So if you weigh 180, the 31 grams of protein per natto serving, would be about 25% the daily recommended value for an adult male. You might want to factor that in to your overall protein intake for the day. On the other hand because it is high in protein it can be a great addition to your morning routine to help boost your metabolism.  Too much protein consumption can cause a whole slew of health conditions like kidney stones and osteoporosis, so you definitely just want to make sure you are taking in a good amount for your age and weight.

When it is all said and done, the positive health benefits far outweigh any risk associated with eating natto. Just keep things balanced, eat a wide variety of fruits and veggies and stay away from the GMO soy!

 Have you tried natto? What did you eat with it? 

Josh Axe

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