by Frank C. Siraguso
The rebels attacked at night. Hachiman Taro Yoshiie and his men had set up camp and were boiling soybeans to feed their horses. Totally surprised, with no time to think, the men packed the hot soybeans in rice-straw sacks, threw them over their horses’ backs, and barely escaped with their lives. (14)
During that year in northeastern Japan, 1051, cold weather, poor crops, and high taxes led peasants to revolt. The Kyoto government had sent Yoshiie, son of a famous general, to quell the uprising. (14)
Facing imminent battle the morning after their escape, Yoshiie and his men were forced to eat the only thing they had on hand – the boiled soybeans. They found the soybeans had fermented overnight and developed a sticky, stringy coating. Today known as natto, those sticky, stringy soybeans gave Yoshiie and his men the strength they needed to win. (14)
The story of Yoshiie is the most popular of several legends describing the origins of natto (not-toe´). Although they have different narratives, the common thread is natto was the happy accident resulting from storing boiled soybeans wrapped in rice straw in a warm place. (14)
Legends aside, the true origins of natto are obscure, although people have eaten soybeans for nearly 5,000 years, and the Chinese and Japanese have eaten fermented soybeans for more than 2,000 years. According to Japanese food historian Naomichi Ishige, the word “natto” originated with vegetarian Buddhist monks who ate lots of fermented soybeans. Loosely, natto means “beans [from] a temple kitchen.” (14) Natto is one of the few soyfoods called by its native name in every European language. (15)
Today in the U.S., Japanese cuisine, notably sushi, has become very popular and common. Some see sushi as a healthy way to eat. Natto, neither as well-known nor as glamorous, may have more important health benefits.
So, just what is natto?
Natto is fermented soybeans
You can ferment foods using bacteria, mold, salt, or yeast, depending on what you are making, such as using salt to make sauerkraut. Soybeans fermented for natto use a specific bacterium, Bacillus subtilis, isolated by Dr. Shin Sawamura in 1905. (14) Sometimes called Bacillus subtilis natto, it’s found naturally in soil, plant roots, and water. (2)
Natto is soybeans with more benefits
Although natto is fermented soybeans, it has the same nutritional benefits of soybeans. (15) According to USDA FoodData Central (16), natto and soybeans each have about 214 calories, 18.2 grams of protein, and 5.5 grams of fiber. Soy protein is as good as animal protein. (8) You get all the essential amino acids you need for proper nutrition. (9)
Natto’s health benefits come from two components: nattokinase, which is unique to natto; and vitamin K2, including MK-7, a specific form of K2. Natto has more MK-7 than practically any other food.( 17) This combination of nattokinase and vitamin K2 gives natto more health benefits than unfermented soybeans.
Nattokinase for vascular health
Natto’s most distinguishing feature is the sticky, stringy, slimy coating that results from fermentation. It contains nattokinase (long I, like “kind”), the protein that provides many of natto’s health benefits. (7)
Dr. Hiroyuki Sumi, at Chicago University Medical School, discovered nattokinase in 1980, which he determined is an enzyme with powerful anticlotting and clot-dissolving properties. It is the “most active ingredient in natto.”(1)
Nattokinase can improve blood flow in people with heart and vascular disease. Its effects are similar to aspirin but without the possible side effects of bleeding or gastric ulcers. (18)
Nattokinase also increases tissue plasminogen activator (t-PA) in the bloodstream, which can help prevent or dissolve blood clots. Unlike pharmaceutical tPA provided as emergency treatment to stroke patients, nattokinase has few or no side effects such as bleeding.(18)
A kinase is an enzyme, a type of protein that speeds up the body’s chemical reactions. It adds sugars or proteins to molecules that may make them active or inactive. For example, certain kinases are linked to cancer, which causes unregulated cell growth. (11) Nattokinase is not related to any of the known kinases. (18)
Vitamin K2 for bone health
Types of vitamin K, a fat-soluble vitamin, include K1 (phylloquinone) and K2 (menaquinone, or MK). K1, generally found in green vegetables, is the predominant form of dietary vitamin K.
Natto has abundant vitamin K2, which can help improve postmenopausal bone density. (4) Vitamin K2 activates bone-building proteins so your bones can better absorb and retain calcium. (12) This helps inhibit osteoporosis without risk of negative side effects or overdosing.(3) Osteoporosis is a chronic loss of bone density that weakens the bones and results in fractures, especially the hips.
The different forms of vitamin K2 include MK-4, MK-7, MK-8 and MK-9. MK-7 is mainly in bacteria-fermented foods. It is the active form of vitamin K2 in natto.(3) Compare the amount of MK-7 in micrograms per 100 grams (3.5 ounces) or 100 milliliters (3.4 liquid ounces) for these foods.(17)
· Natto – 900 to 1,000
· Hard cheese – 2.3
· Whole milk (per 100 milliliters) – 2.0
· Yogurt (per 100 milliliters) – 0.4
· Sauerkraut – 0.2
Types of natto
The most common type of natto is made from yellow soybeans, although there is also black soybean natto. Otherwise, natto types are based on soybean size – large, medium and small, with some in-between sizes. Another type is hikiwari natto, where the beans are broken into small pieces before fermenting. Personally, I like smaller soybean sizes, but they all taste the same. You’ll learn which you like best.
Get natto at Asian markets
You can find natto in Asian groceries in the frozen food section. Natto comes in a 3-inch square single-serving foam box or, sometimes, a little round cup, in a bundle of 2 to 4, for about $3.
They are wrapped in a plastic label, always in Japanese, which I don’t read. The FDA nutrition facts label, pasted to the bundle, is in English, but it doesn’t tell you about the type of natto.
Each box or cup has 40-45 grams (about 1.5 ounces) of natto. There are also small plastic packets of hot yellow mustard and soy sauce. The soy sauce is often a custom blend for each brand of natto. Not every brand of natto has mustard and soy sauce. As you try different brands, you’ll learn which ones you like and what comes in the box, so to speak.
What I did was buy several brands at random and take photos of brands I liked and, just as important, those I disliked. Be ready to improvise – you may not always find the same brands consistently.
Get natto online
You can also buy natto online, with several brands made in the U.S. Depending on the seller, your natto may ship frozen or in a cold-pack box. Instead of the foam boxes, your natto may come in a glass jar with a lid or some type of resealable container you can recycle after the natto is gone. Keep these in the fridge.
Instead of the individual servings, bulk natto usually has several servings per container. Simply spoon out the amount you want, close the container tightly and return to the fridge. You’ll need your own mustard and soy sauce.
Hachiman and his men ate their natto out of the same rice-straw bags they had put the soybeans in before escaping. Today, you can eat natto out of the little box or put it in a bowl.
The Japanese – even their kids – eat natto as part of breakfast.(9) They put it on a bowl of hot rice, sometimes with chopped green onion. But they – and you – can eat natto anytime you want, with a variety of foods including kimchi, daikon (giant radish), and okra. You can experiment and find what combination you like.
As you stir in the soy sauce, mustard and other ingredients, your natto will become more and more stringy. These sticky strings are the secret to natto’s benefits. If you eat your natto plain, you should still stir it up first.
Smell and taste
Natto’s smell and taste have been described as earthy or funky, like strong cheese, or musty.(15) But sometimes natto has an ammonia smell. Natto is fairly perishable, and improper storage can cause overfermentation, developing ammonia.(14) This causes amino acids to break down, reducing the natto’s quality. In my experience, natto that has overfermented can be mushy in texture.
Sometimes natto straight from the store has an ammonia smell. Sadly, you won’t know until you get the natto home and open it. If your natto smells of ammonia, don’t eat it. If possible, return it to the store. I have found that some brands are more likely than others to be affected this way, and learned to avoid them. Again, take photos of the labels!
Make natto at home
The Japanese first made natto by wrapping warm, cooked soybeans in rice-straw bundles, and letting them sit at room temperature. Since the 1920s, they use a culture like Bacillus natto to make natto.(14)
The traditional process of fermenting soybeans to make natto is simple and straightforward and can be easily done at home. Bacillus subtilis (natto) is the starter used to make natto, commercially and at home. (18) It’s like a science project combined with canning veggies.
Preparing the beans takes time but the most important thing is to have a sterilized, oven-safe dish and a sterilized spoon. When you have prepared the soybeans, you have to keep them at a steady temperature of 100 F for 24 hours. After that, put them in the fridge to complete fermentation for another 24 hours. You can find detailed instructions online.
1. Chen, H., McGowan, E., Ren, N., Lal, S., Nassif, N., Shad-Kaneez, S.,Qu, X., & Lin, Y., (2018).
Nattokinase: A promising alternative in prevention and treatment of cardiovascular diseases. Biomarker Insights, Vol. 13: 1–8
2. Earl, A., Losick, R., Kolter, R., (2008). Ecology and genomics of Bacillus subtilis. Trends in
Microbiology, 16(6): 269
3. Halder, M., Petsophonsakul, P., Akbulut, A. C., Pavlic, A., Bohan, F., Anderson, E., Maresz, K.,
Kramann, & R., Schurgers, L. (2019). Vitamin K: Double bonds beyond coagulation insights into differences between vitamin K1 and K2 in health and disease. International Journal of Molecular Sciences, 20(4), 896, http://dx.doi.org/10.3390/ijms20040896
4. Ikeda, Y., Iki, M., Morita, A., Kajity, E., Kagamimori, S., Kagawa, Y., Yoneshima, H. (2006). Intake of
fermented soybeans, natto, is associated with reduced bone loss in postmenopausal women: Japanese population-based osteoporosis (JPOS) study. American Society for Nutrition, 0022-3166/06
5. Jang, J-Y., et al. (2013). Nattokinase improves blood flow by inhibiting platelet aggregation and
thrombus formation. Laboratory Animal Research, December, 2013, Vol. 29, No. 4
6. Japan Nattokinase Association, (2021). What is Bacillus subtilis natto?
7. Kurosawa, Y. et al. A single-dose of oral nattokinase potentiates thrombolysis and
anti-coagulation profiles. Sci. Rep. 5, 11601; doi: 10.1038/srep11601 (2015)
8. MedlinePlus Medical Encyclopedia, (2019). Soy. https://medlineplus.gov/ency/article/007204.htm
9. Michelfelder, A. J., MD, (2009). Soy: A complete source of protein. American Family Physician,
Vol. 79, No. 1, pp. 43-47
10. New York Times Magazine, (2014). Rise and Shine. What kids around the world eat for breakfast.
11. NIH National Cancer Institute Publications, Dictionaries. Kinase:
12. Petri, A., MS, ( 2017). Why natto is super healthy and nutritious. Healthline,
13. Schwalfenberg, G. K., (2017). Vitamins K1 and K2: The emerging group of vitamins required for
human health. Journal of Nutrition and Metabolism, Vol. 2017, https://doi.org/10.1155/2017/6254836
14. Shurtleff, W., & Aoyagi, A., (2012). History of natto and its relatives (1405-2012). Soyinfo Center,
15. Shurtleff, W., & Aoyagi, A., (2004). History of natto and its relatives. Soyinfo Center,
16. USDA FoodData Central. https://fdc.nal.usda.gov/index.html;
17. Walther, B., Karl, P., Booth, S. L., & Boyaval, P., (2013). Menaquinones, bacteria, and the food
supply: The relevance of dairy and fermented food products to vitamin K requirements. American Society for Nutrition, Vol. 4, No. 4, pp. 463–473, https://doi.org/10.3945/an.113.003855
18. Weng,Y., Yao, J., Sparks, S., & Wang K.J., (2017). Nattokinase: an oral antithrombotic agent for the prevention of cardiovascular disease. International Journal of Molecular Science, 18: 523
19. Yamaguchi, M., (2006). Regulatory mechanism of food factors in bone metabolism and prevention of osteoporosis. Yakugaku Zasshi (Pharmaceutical Science Journal), 126 (11) 1117–1137, The Pharmaceutical Society of Japan
Photo credit: Tim Pott
Frank Siraguso has a years-long interest in the concept of food as medicine. He started as a medical-healthcare writer in 2005, when he started work in the Communications Department at The University of Kansas Health System. He has been a freelance medical-healthcare writer since 2013. Frank has also worked in web writing and design, and has reviewed theater productions and books. He recently published a book on his experience as a bass player in an Elvis impersonator band, “He Don’t Look Like Elvis.” Frank lives in Midtown with his spouse, Molly O’Leary, DC.