Natto: Benefits, Nattokinase, Vitamin K2 & How to Eat It

Dr. Josh Axe · Free quiz

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Natto is a traditional Japanese food made by fermenting cooked whole soybeans with Bacillus subtilis, which turns them sticky, stringy and deeply savory. It's one of the fermented organic soy foods I recommend, because a small pack brings plant protein, iron and one of the richest food sources of vitamin K2, plus nattokinase, an enzyme that helps your body break down excess fibrin in the blood.11291310

Both of those work with systems your body already runs. Your body was designed to build calcium into your bones and teeth and keep it out of your artery walls, and vitamin K2 is the nutrient it uses to steer calcium where it belongs.10 Your body also lays down fibrin to stop bleeding and then breaks it down again once the job is done, and nattokinase lends a hand with that cleanup.1014 So when you eat natto, you're feeding two jobs your body is built to do, protecting your bones and keeping your blood flowing.

People in Japan have eaten natto for more than a thousand years, mostly over rice.21 Japan has one of the longest lifespans in the world, and I think part of that is the Bacillus subtilis people there take in through fermented foods like natto.15 On soy in general, this is the line I draw:

Did you know?

• The word natto appears in a Japanese document as early as 1068.1

• Women in Tokyo, where natto is a common food, had blood vitamin K2 levels of 5.26 ng/mL, against 1.22 in Hiroshima, where it's seldom eaten, and 0.37 in Britain.16

• In a study of young Japanese women, about a quarter of their vitamin K came as MK-7, the form natto is rich in, most of it from beans and soybean foods like natto.13

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What is natto?

The threads are the first thing you notice when you open a pack and give it a stir. They're made of chains of glutamic acid, an amino acid, which the bacteria produce as they ferment the beans,2 and they stretch from the beans to your chopsticks like strands of melted cheese. The natto strain of Bacillus subtilis is a hardy organism that stays active from pH 6 to 12 and at temperatures up to 140°F (60°C),2 and it's the bacterium itself that makes natto's two most valuable products, vitamin K2 and nattokinase.34

Natto belongs to the same family of fermented whole-soy foods as miso and tempeh, and all three belong among the traditional fermented foods. Fermentation is what sets them apart from processed soy, because the beans stay whole and the microbes do part of the digesting for you.1718

A short history of natto

The word natto shows up in a Japanese document as early as 1068, though back then it named a salted, mold-fermented soybean rather than the sticky food we know today.1 A Japanese food book from 1695 traces the name to nassho, the word for the kitchen in a Buddhist temple, literally a "place of offering."1 For centuries, families made natto by wrapping cooked soybeans in rice straw, which carries Bacillus subtilis naturally, and keeping the bundles warm overnight. In 1905 a Japanese researcher named Sawamura isolated the bacterium, and pure starter cultures later let makers produce natto without straw.1 Natto is eaten most of all north of Tokyo and in the six prefectures of the northeast, and much less in the west and south of the country.2116

The long-lived Japanese way of eating pairs rice with fermented foods like miso, natto and pickled vegetables,10 and natto still turns up on breakfast tables there, stirred and spooned over a bowl of warm rice. When a food stays on the table that long, it's worth asking what it gives the people who eat it, and research over the last few decades has started to show what that is.

What does natto taste like?

Natto tastes savory, nutty and earthy, with a deep, almost cheesy richness, and the scientists who discovered its enzyme even called it a vegetable cheese.4 What takes getting used to is the smell and the texture. A review of nattokinase research calls natto's odor and stringy texture a major drawback to eating it as an everyday food,2 and the threads multiply the more you stir, stretching from the bowl to your chopsticks.

If you're trying it for the first time, a few small moves make it easier to enjoy. Stir the natto well before you season it, so the threads turn light and foamy, then add the little packet of mustard and a splash of coconut aminos. Spoon it over warm rice with sliced scallions, where the rice softens both the flavor and the smell, or mix it with kimchi or avocado. Starting with half a pack is perfectly fine while you get used to it.

Natto nutrition facts

Per pack and per 100 grams, from USDA FoodData Central (FDC 172443), with % Daily Value in parentheses. A pack is about 40 grams.95

USDA's record measures only vitamin K1, 23.1 micrograms per 100 grams, so it leaves out the vitamin K2 that natto is known for.9 Lab tests of ordinary natto found about 775 micrograms of K2, in the form called MK-7, per 100 grams, and a second analysis of 58 foods found about 940, so a 40-gram pack carries roughly 310 to 375 micrograms.313

Natto's protein contains all nine essential amino acids,9 so a pack adds 7.8 grams of plant protein that pairs well with an egg or a piece of wild fish to round out a meal. Its minerals stand out as well: per 100 grams, natto gives you about three-quarters of a day's copper and two-thirds of a day's manganese, and its magnesium and potassium are two of the minerals your blood vessels need in order to relax.919 For the iron side of the story, our guide to iron-rich foods covers the other everyday sources.

Is natto good for you?

Soy is one of the most argued-about foods in nutrition, and fermented, organic soy like natto is the kind I recommend over processed soy.17 The Japanese research lines up with that distinction. In a large Japanese cohort study that ran for nearly 15 years, total soy intake had no link with the risk of dying, while the men and women who ate the most fermented soy had about a 10% lower risk.6

How the soy is grown matters as much as how it's made. My rule for soy is that it should be organic, natural and nonprocessed,21 and in The Biblio Diet, organic soybeans are on the eat list while non-organic soybeans and soy protein powder are on the avoid list.22 A pack of organic natto meets all of that, since the beans themselves are nothing but whole organic soybeans and a bacterium. That's food as medicine: a traditional food your body knows what to do with, made better by the way it's prepared.

How natto works in your body

Natto works through two things the bacteria make while the beans ferment. Vitamin K2 helps your body put calcium in the right places, building it into bone and keeping it out of your artery walls, and nattokinase helps your blood break down fibrin, the protein mesh that holds a clot together.1014 This is the path a pack of natto takes, from the fermenting bean to your bones and your bloodstream:

Natto's vitamin K2: calcium into bone, not arteries

Vitamin K2 directs calcium into your bones and teeth, where it belongs, and it works hand in hand with vitamin D, which is why I pair the two.10 In my High Blood Pressure Protocol, K2 sits in the essential tier of the supplement plan for that reason,19 and you can picture it as a traffic officer for calcium, waving it into your bones and away from your vessel walls, where calcium deposits make arteries stiff.

The K2 in natto is the MK-7 form, and it's the form that lasts. In healthy volunteers, MK-7 from natto stayed in the blood far longer than vitamin K1, so with a daily dose its levels built up 7- to 8-fold, and it activated osteocalcin more completely than K1 did.25 My supplement dose for K2 is 100 to 200 micrograms a day with a meal that has some fat,10 and a single pack of natto gives you more than that, in a food that comes with its own fat.39 Our guide to vitamin K foods shows where natto sits among the other sources.

Natto benefits

The cards below start with bones and the heart, where the evidence is strongest, and each badge shows the kind of study behind the benefit.

Nattokinase: what it is, what the trials show and how much to take

Nattokinase is the reason natto can break down fibrin, and researchers in Japan first described it in 1987.4 It belongs to the family of proteolytic enzymes, the enzymes that break down proteins, and related enzymes turn up in other fermented soybean foods, including Thai thua nao, Chinese douchi and Korean doen-jang,2 so natto is the best-known source rather than the only one. What makes it useful as a supplement is that it seems to survive digestion. In a pilot study of 11 healthy adults, nattokinase showed up in the blood within 2 hours of a single 100-milligram capsule and peaked at about 13 hours; that capsule is the standard 2,000 fibrinolytic units (FU) you'll see on labels.332

Nattokinase and blood pressure

As I see it, high blood pressure is what your arteries and kidneys do when insulin runs high, the minerals that relax your vessels run low and your nervous system is stuck in overdrive.19 Nattokinase is one helper alongside those bigger levers, and its trials have focused on people whose pressure runs high.

In a placebo-controlled trial in Korea with ties to the supplement's maker, 86 adults with untreated, mildly high blood pressure took 2,000 FU of nattokinase or a placebo for 8 weeks, and among the 73 who finished, nattokinase lowered systolic pressure by 5.55 points and diastolic by 2.84 more than placebo did.34 A North American placebo-controlled trial, sponsored by the product's U.S. distributor, found a similar pattern in 79 adults with high blood pressure, 74 of whom finished. After 8 weeks on 100 milligrams a day of a nattokinase with its vitamin K2 removed, diastolic pressure averaged 84 mmHg in the nattokinase group against 87 on placebo, and in men it fell from 86 to 81, while men on placebo stayed at 88. Systolic pressure dipped as well, from 144 to 140, but not by more than it did on placebo.35

When researchers pooled three 8-week placebo-controlled trials with 223 people in all, the two above plus one in people with high cholesterol, nattokinase lowered systolic pressure by 3.45 points and diastolic by 2.32 compared with placebo.8 In a placebo-controlled trial of 265 healthy adults with no heart disease, 2,000 FU a day for about 3 years didn't change blood pressure,36 so nattokinase looks most useful when your pressure is already running above where it should be.

Nattokinase and blood clots

Nattokinase tips your blood toward clearing fibrin, and the shift shows up within hours of a single capsule. In a study in which 12 healthy young Japanese men each tried both a single 2,000 FU capsule and a placebo, nattokinase raised fibrin and fibrinogen breakdown products at 4 hours and D-dimer, another marker of clot breakdown, at 6 and 8 hours. It also lowered factor VIII, one of the clotting proteins, at 4 and 6 hours, and every change stayed within the normal range.14 In a 2-month study in Taiwan, 45 adults, some healthy, some with risk factors for heart disease and some on dialysis, took 2,000 FU twice a day. Their fibrinogen fell 7% to 10% across the groups, factor VII fell 7% to 14% and factor VIII fell 17% to 19%; there was no placebo group, and people knew what they were taking.32 These studies measured how blood clots and clears rather than counting clots, and fibrinogen is the raw material your body turns into fibrin, so lower levels mean less of it is on hand to build a clot.

Nattokinase and artery plaque

In people who already have carotid plaque, higher doses of nattokinase have shrunk it. A records study from China with no untreated or placebo group followed 1,062 adults with high cholesterol who took 10,800 FU a day for 12 months, and in the 683 who had carotid plaque, plaque area fell 36.0%, while 3,600 FU a day changed nothing; five of its authors worked for an enzyme maker.37 In healthy adults at the usual 2,000 FU, the 3-year placebo-controlled trial of 265 people found no slowing of artery-wall thickening.36

In a randomized trial, 82 outpatients with carotid plaque and high cholesterol took either 6,000 FU of nattokinase a day or 20 milligrams of the statin simvastatin for 26 weeks, and people knew which treatment they got. Among the 76 who finished, plaque area shrank 36.6% on nattokinase against 11.5% on the statin. The statin lowered total cholesterol, LDL and triglycerides more, and nattokinase raised HDL.38 In the pooled placebo-controlled trials, though, nattokinase didn't lower cholesterol: in the two 8-week trials, total cholesterol came out about 5 points higher than on placebo and LDL about 6.5 higher, and in the two longer trials, total cholesterol was about 3 points higher.8 So in the one head-to-head trial, nattokinase did more for the plaque itself, and the statin did more for cholesterol.

Natto or a nattokinase supplement?

You can get nattokinase two ways, and I've laid out both on my show:

Natto is the food-first choice, because the pack brings the enzyme along with vitamin K2, protein, iron, fiber and live Bacillus subtilis.93 A supplement gives you a measured dose of the enzyme, the way the trials gave it, and some products, like the one in the North American blood pressure trial, have the vitamin K2 taken out.35 In the study that discovered it, natto's enzyme was measured in a lab unit that doesn't convert to the FU on a supplement label,4 so there's no reliable figure for how many capsules a pack equals. If you enjoy natto, eat it, and if you want the trial dose or can't warm up to the taste, a supplement is the measured route.

How much nattokinase?

Nattokinase is on my list of supplements for heart health in Heal Your Cells, because it helps break down excess fibrin in the blood and supports healthy circulation.10 If you take a blood thinner or aspirin, read the safety section below before you start. My dose is 100 to 200 milligrams a day, taken on an empty stomach for best absorption,10 which on a standard product works out to about 2,000 to 4,000 FU, the same amounts used in the clot-breakdown studies above.21432 When you shop, check the label for the FU count as well as the milligrams. The 6,000 and 10,800 FU doses in the plaque studies were study doses rather than everyday amounts,3837 so stay within the 100-to-200-milligram range and take your capsule between meals.

How to eat natto (and how to use it)

Natto is eaten cold or at room temperature, straight from the pack, and it's easy to fold into meals you already make. Here are the simplest ways to use it:

Keep natto warm rather than hot. Nattokinase holds up to about 122°F (50°C) and the natto bacterium to about 140°F (60°C),2 and in one test, boiled natto raised people's blood vitamin K2 far less than ordinary natto did,23 so stir it into food after the food comes off the heat.

How often should you eat natto?

One pack, about 40 grams, several times a week up to once a day is a good everyday amount. Natto is an everyday food in the parts of Japan where it's a staple,16 and that range matches the research: women who ate seven or more packs a week had the fewest fractures, the adults in the top fifth for natto ate more than 26 grams a day, and men who ate natto a few times a week carried more vitamin K2 in their blood.563 If the taste is new to you, start with half a pack a few times a week and build from there.

Where to buy natto (and what to look for)

You'll find natto in the refrigerated or freezer section of Japanese and Asian grocery stores, in many natural food stores and online. It usually comes as a stack of small cups, each with a packet of mustard and a packet of soy-based sauce. Choose packs made from organic soybeans, and read the sauce packet's label, since it can contain wheat-based soy sauce and added sugar; if you'd rather skip it, coconut aminos or a gluten-free organic tamari works well. Keep natto in the refrigerator and eat it by the date on the pack, or freeze it and thaw it in the fridge overnight.

Natto recipes

Start with the classic bowl, then try natto the other ways below. None of them call for heating the natto itself, which keeps its enzyme and bacteria intact.

• Natto hand roll. Lay a sheet of nori in your hand, add a spoonful of warm rice, natto, cucumber, avocado and flaked smoked wild salmon, then roll it into a cone.

• Natto miso soup. Make our miso soup, take it off the heat, and stir in a pack of natto and sliced scallions just before serving.

• Natto avocado toast. Toast a slice of sourdough bread, spread it with mashed avocado, and top it with natto, sesame seeds and a pinch of chili flakes.

• Natto kimchi bowl. Fill a bowl with warm rice, natto, a soft-cooked egg and a spoonful of homemade kimchi, then finish it with toasted sesame oil.

How to make natto at home

Making natto at home takes a natto starter (dried Bacillus subtilis spores, sold online), a way to hold the beans warm and about a day and a half from soaking to finished natto. Because you're growing a bacterium, scald your bowls, spoons and dish with boiling water first so the natto strain is the one that takes hold.

1. Soak. Cover 1 pound (about 2 cups) of organic soybeans with plenty of water and soak them for 9 to 12 hours, until they've roughly doubled in size.

2. Cook until tender. Steam or pressure-cook the beans until one crushes easily between your thumb and finger, then drain them well.

3. Add the starter. While the beans are still hot, mix in the natto starter as the package directs, usually dissolved in a spoonful of boiled and cooled water, and stir with a clean spoon.

4. Spread and cover. Spread the beans no more than an inch deep in a clean glass or ceramic dish, and cover it with a clean cloth so air can reach them.

5. Ferment warm. Hold the beans at about 104°F (40°C) for 14 to 18 hours, in a yogurt maker, a dehydrator or an oven with only the light on, checking the temperature with a thermometer, until they're coated in a white film and pull into sticky threads.1

6. Chill. Let the natto cool, pack it into small containers and refrigerate it, and freeze any you won't eat within a few days.

Natto side effects and who should skip it

For most people, natto is simply good food, and the cautions below apply to a few specific groups.

Never swap a prescribed blood thinner for nattokinase. In one documented case, a man who replaced warfarin with nattokinase after a mechanical heart valve replacement developed a clot on the valve and needed surgery again,42 and in another, a man on aspirin bled into his brain after a week of 400 milligrams of nattokinase a day, four times the usual capsule.39 Before surgery, tell your surgeon you take nattokinase and stop it when they advise.

A low thyroid. The soy my Hypothyroidism Protocol lists among the foods that work against the thyroid is unfermented soy, and natto is fermented, organic soy.46 In a review of 18 randomized trials, soy didn't change thyroid hormone levels, though TSH rose slightly.47 If you take thyroid medication, space it from natto as the interaction check describes, and your doctor can recheck your TSH if your soy intake changes a lot.

Soy or natto allergy. About 0.6% of U.S. adults have a soy allergy,44 and anyone with one should skip natto. Natto can also cause a rare, delayed allergy to its sticky threads, with symptoms that start hours after eating; in one clinic, 11 of 13 people with natto allergy were surfers, who may have been sensitized by jellyfish stings.4548 If you get itchy, swollen or short of breath hours after natto, stop eating it and get tested, and treat trouble breathing as an emergency.

Very weak immunity. In a study that compared 23 children on chemotherapy for cancer who developed a Bacillus subtilis bloodstream infection with 92 similar children who didn't, those who had eaten natto in the week before had 3.3 times the odds of infection.49 In a records review at one Japanese hospital, 69 of 70 Bacillus subtilis blood samples carried the natto strain, mostly from older patients with abdominal infections.50 If you're on chemotherapy or severely immunocompromised, ask your care team before eating natto.

The bottom line

Natto: frequently asked questions

References

1. Shurtleff W, Aoyagi A. History of Natto and Its Relatives (Page 1). Soyinfo Center, Lafayette, California; 2004 ("natto" first in a Japanese document in 1068; straw method; Sawamura isolated Bacillus natto in 1905; fermentation at 40°C (104°F) for 14-18 hours; northeast Japan).
2. Weng Y, Yao J, Sparks S, Wang KY. Nattokinase: An Oral Antithrombotic Agent for the Prevention of Cardiovascular Disease. Int J Mol Sci. 2017;18(3). doi:10.3390/ijms18030523
3. Tsukamoto Y, Ichise H, Kakuda H, Yamaguchi M. Intake of fermented soybean (natto) increases circulating vitamin K2 (menaquinone-7) and gamma-carboxylated osteocalcin concentration in normal individuals. J Bone Miner Metab. 2000;18(4):216-22. doi:10.1007/s007740070023
4. Sumi H, Hamada H, Tsushima H, Mihara H, Muraki H. A novel fibrinolytic enzyme (nattokinase) in the vegetable cheese Natto; a typical and popular soybean food in the Japanese diet. Experientia. 1987;43(10):1110-1. doi:10.1007/BF01956052
5. Kojima A, Ikehara S, Kamiya K, Kajita E, Sato Y, Kouda K, et al. Natto Intake is Inversely Associated with Osteoporotic Fracture Risk in Postmenopausal Japanese Women. J Nutr. 2020;150(3):599-605. doi:10.1093/jn/nxz292
6. Katagiri R, Sawada N, Goto A, Yamaji T, Iwasaki M, Noda M, et al. Association of soy and fermented soy product intake with total and cause specific mortality: prospective cohort study. BMJ. 2020;368:m34. doi:10.1136/bmj.m34
7. Nagata C, Wada K, Tamura T, Konishi K, Goto Y, Koda S, et al. Dietary soy and natto intake and cardiovascular disease mortality in Japanese adults: the Takayama study. Am J Clin Nutr. 2017;105(2):426-431. doi:10.3945/ajcn.116.137281
8. Li X, Long J, Gao Q, Pan M, Wang J, Yang F, et al. Nattokinase Supplementation and Cardiovascular Risk Factors: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Rev Cardiovasc Med. 2023;24(8):234. doi:10.31083/j.rcm2408234
9. U.S. Department of Agriculture, Agricultural Research Service. Natto. FoodData Central, SR Legacy, FDC ID 172443 (NDB 16113). Per 100 g: 211 kcal; protein 19.4 g; fat 11.0 g; carbohydrate 12.7 g; fiber 5.4 g; calcium 217 mg; iron 8.6 mg; magnesium 115 mg; phosphorus 174 mg; potassium 729 mg; sodium 7 mg; zinc 3.03 mg; copper 0.667 mg; manganese 1.53 mg; selenium 8.8 µg; vitamin C 13.0 mg; vitamin K (phylloquinone) 23.1 µg; 1 cup = 175 g.
10. Axe J, Cole W. Heal Your Cells. Avery; 2026. ISBN 9798217181353 (chapter "Reversing Heart Age": p. 367, vitamin K2 (MK-7), 100-200 mcg a day with fat-containing meals, works with vitamin D; p. 368, nattokinase, helps break down excess fibrin in the blood, 100-200 mg a day on an empty stomach; Japanese longevity diets pair rice with fermented foods like miso, natto and pickled vegetables).
11. Theuwissen E, Teunissen KJ, Spronk HM, Hamulyák K, Ten Cate H, Shearer MJ, et al. Effect of low-dose supplements of menaquinone-7 (vitamin K2 ) on the stability of oral anticoagulant treatment: dose-response relationship in healthy volunteers. J Thromb Haemost. 2013;11(6):1085-92. doi:10.1111/jth.12203
12. Axe J. Women NEED to Know This Before Getting on HRT. The Dr. Josh Axe Show. 2026 (Dr. Axe, solo episode: fermented organic soy, like tempeh, miso and natto, and menopausal symptoms at 30:50; YouTube https://www.youtube.com/watch?v=rcPa3Wnl_CI&t=1850s).
13. Kamao M, Suhara Y, Tsugawa N, Uwano M, Yamaguchi N, Uenishi K, et al. Vitamin K content of foods and dietary vitamin K intake in Japanese young women. J Nutr Sci Vitaminol (Tokyo). 2007;53(6):464-70. doi:10.3177/jnsv.53.464
14. Kurosawa Y, Nirengi S, Homma T, Esaki K, Ohta M, Clark JF, et al. A single-dose of oral nattokinase potentiates thrombolysis and anti-coagulation profiles. Sci Rep. 2015;5:11601. doi:10.1038/srep11601
15. Axe J. The #1 Supplement to Heal Your Gut, Burn Fat, and Boost Immunity. The Dr. Josh Axe Show. 2025 (Dr. Axe, solo episode: Bacillus subtilis in natto and the Japanese diet at 15:39; protease and amylase at 16:38; natto and Bacillus subtilis at 21:47; nattokinase and vitamin K2 in natto at 23:20; YouTube https://www.youtube.com/watch?v=q-1THW9kLB0&t=1400s).
16. Kaneki M, Hodges SJ, Hosoi T, Fujiwara S, Lyons A, Crean SJ, et al. Japanese fermented soybean food as the major determinant of the large geographic difference in circulating levels of vitamin K2: possible implications for hip-fracture risk. Nutrition. 2001;17(4):315-21. doi:10.1016/s0899-9007(00)00554-2
17. Axe J. Natural Sunscreens, EMF Exposure, & the Best Dairy Alternatives | Q&A. The Dr. Josh Axe Show. 2024 (Dr. Axe, solo Q&A: processed soy vs natto, tempeh and miso at 39:29; YouTube https://www.youtube.com/watch?v=C-HsQGa7aOo&t=2369s).
18. Axe J. 10 Signs You Have an Iron Deficiency (How to Boost Iron Naturally). The Dr. Josh Axe Show. 2024 (Dr. Axe, solo episode: phytates, non-heme iron, sprouting and fermentation at 21:59; YouTube https://www.youtube.com/watch?v=JjlsPil8ZSE&t=1319s).
19. Axe J. The High Blood Pressure Protocol: A Root-Cause Approach. DrAxe.com protocol. 2026 (p. 3, "A letter to everyone told they'd be on pills for life": the root causes of high blood pressure and the 5-step path used with patients; top 10 blood-pressure-healing foods, #5 beans and lentils; supplement protocol, Essential tier: vitamin D3 + K2, "K2 steers calcium to bone, not arteries").
20. Knapen MH, Drummen NE, Smit E, Vermeer C, Theuwissen E. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int. 2013;24(9):2499-507. doi:10.1007/s00198-013-2325-6
21. Axe J. 6 Things Disrupting Women's Hormones (and How to Balance Hormones Naturally). The Dr. Josh Axe Show. 2025 (Dr. Axe, solo episode: organic, natural, nonprocessed soy at 47:26; YouTube https://www.youtube.com/watch?v=V9fLgt6Czpk&t=2846s).
22. Axe J, Rubin J. The Biblio Diet. Hachette Book Group; 2025. ISBN 9781546008439 (food lists: "Beans and legumes (soaked or pressure-cooked are best)" with miso, tempeh and organic soybeans on the eat list; nonorganic soybeans and soy protein powder on the avoid list; "Note: Buy organic when possible").
23. Homma K, Wakana N, Suzuki Y, Nukui M, Daimatsu T, Tanaka E, et al. Treatment of natto, a fermented soybean preparation, to prevent excessive plasma vitamin K concentrations in patients taking warfarin. J Nutr Sci Vitaminol (Tokyo). 2006;52(5):297-301. doi:10.3177/jnsv.52.297
24. Knapen MH, Braam LA, Drummen NE, Bekers O, Hoeks AP, Vermeer C. Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women. A double-blind randomised clinical trial. Thromb Haemost. 2015;113(5):1135-44. doi:10.1160/TH14-08-0675
25. Schurgers LJ, Teunissen KJ, Hamulyák K, Knapen MH, Vik H, Vermeer C. Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood. 2007;109(8):3279-83. doi:10.1182/blood-2006-08-040709
26. Macfarlane BJ, van der Riet WB, Bothwell TH, Baynes RD, Siegenberg D, Schmidt U, et al. Effect of traditional oriental soy products on iron absorption. Am J Clin Nutr. 1990;51(5):873-80. doi:10.1093/ajcn/51.5.873
27. Garvey SM, Mah E, Blonquist TM, Kaden VN, Spears JL. The probiotic Bacillus subtilis BS50 decreases gastrointestinal symptoms in healthy adults: a randomized, double-blind, placebo-controlled trial. Gut Microbes. 2022;14(1):2122668. doi:10.1080/19490976.2022.2122668
28. Ikeda Y, Iki M, Morita A, Kajita E, Kagamimori S, Kagawa Y, et al. Intake of fermented soybeans, natto, is associated with reduced bone loss in postmenopausal women: Japanese Population-Based Osteoporosis (JPOS) Study. J Nutr. 2006;136(5):1323-8. doi:10.1093/jn/136.5.1323
29. Liu Y, He Y, He B, Kong L. The Anti-osteoporosis Effects of Natto on Bone Mineral Density in Perimenopausal Women. Curr Med Chem. 2021;28(25):5191-5200. doi:10.2174/0929867327666200306123140
30. Geleijnse JM, Vermeer C, Grobbee DE, Schurgers LJ, Knapen MH, van der Meer IM, et al. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr. 2004;134(11):3100-5. doi:10.1093/jn/134.11.3100
31. Nozue M, Shimazu T, Sasazuki S, Charvat H, Mori N, Mutoh M, et al. Fermented Soy Product Intake Is Inversely Associated with the Development of High Blood Pressure: The Japan Public Health Center-Based Prospective Study. J Nutr. 2017;147(9):1749-1756. doi:10.3945/jn.117.250282
32. Hsia CH, Shen MC, Lin JS, Wen YK, Hwang KL, Cham TM, et al. Nattokinase decreases plasma levels of fibrinogen, factor VII, and factor VIII in human subjects. Nutr Res. 2009;29(3):190-6. doi:10.1016/j.nutres.2009.01.009
33. Ero MP, Ng CM, Mihailovski T, Harvey NR, Lewis BH. A pilot study on the serum pharmacokinetics of nattokinase in humans following a single, oral, daily dose. Altern Ther Health Med. 2013;19(3):16-9.
34. Kim JY, Gum SN, Paik JK, Lim HH, Kim KC, Ogasawara K, et al. Effects of nattokinase on blood pressure: a randomized, controlled trial. Hypertens Res. 2008;31(8):1583-8. doi:10.1291/hypres.31.1583
35. Jensen GS, Lenninger M, Ero MP, Benson KF. Consumption of nattokinase is associated with reduced blood pressure and von Willebrand factor, a cardiovascular risk marker: results from a randomized, double-blind, placebo-controlled, multicenter North American clinical trial. Integr Blood Press Control. 2016;9:95-104. doi:10.2147/IBPC.S99553
36. Hodis HN, Mack WJ, Meiselman HJ, Kalra V, Liebman H, Hwang-Levine J, et al. Nattokinase atherothrombotic prevention study: A randomized controlled trial. Clin Hemorheol Microcirc. 2021;78(4):339-353. doi:10.3233/CH-211147
37. Chen H, Chen J, Zhang F, Li Y, Wang R, Zheng Q, et al. Effective management of atherosclerosis progress and hyperlipidemia with nattokinase: A clinical study with 1,062 participants. Front Cardiovasc Med. 2022;9:964977. doi:10.3389/fcvm.2022.964977
38. Ren NN, Chen HJ, Li Y, Mcgowan GW, Lin YG. [A clinical study on the effect of nattokinase on carotid artery atherosclerosis and hyperlipidaemia]. Zhonghua Yi Xue Za Zhi. 2017;97(26):2038-2042. (Chinese-language article.)
39. Chang YY, Liu JS, Lai SL, Wu HS, Lan MY. Cerebellar hemorrhage provoked by combined use of nattokinase and aspirin in a patient with cerebral microbleeds. Intern Med. 2008;47(5):467-9. doi:10.2169/internalmedicine.47.0620
40. Dobre MZ, Virgolici B, Doicin IC, Vîrgolici H, Stanescu-Spinu II. Navigating the Effects of Anti-Atherosclerotic Supplements and Acknowledging Associated Bleeding Risks. Int J Mol Sci. 2025;26(20). doi:10.3390/ijms262010183
41. Nakajima T, Taya Y, Nishikawa T, Kitamura Y, Kato H, Mathis BJ, et al. First Clinical Trial of a Newly Developed, Low Menaquinone-7, Fermented Soybean Natto in Warfarin-Dependent Patients. J Med Food. 2021;24(8):860-865. doi:10.1089/jmf.2021.0036
42. Elahi MM, Choi CH, Konda S, Shake JG. Consequence of patient substitution of nattokinase for warfarin after aortic valve replacement with a mechanical prosthesis. Proc (Bayl Univ Med Cent). 2015;28(1):81-2. doi:10.1080/08998280.2015.11929198
43. Wiesner A, Gajewska D, Paśko P. Levothyroxine Interactions with Food and Dietary Supplements-A Systematic Review. Pharmaceuticals (Basel). 2021;14(3). doi:10.3390/ph14030206
44. Gupta RS, Warren CM, Smith BM, Jiang J, Blumenstock JA, Davis MM, et al. Prevalence and Severity of Food Allergies Among US Adults. JAMA Netw Open. 2019;2(1):e185630. doi:10.1001/jamanetworkopen.2018.5630
45. Inomata N, Nomura Y, Ikezawa Z. Involvement of poly (γ-glutamic acid) as an allergen in late-onset anaphylaxis due to fermented soybeans (natto). J Dermatol. 2012;39(4):409-12. doi:10.1111/j.1346-8138.2011.01282.x
46. Axe J. The Hypothyroidism Protocol. DrAxe.com protocol. 2026 (p. 17, thyroid foods ranked: unfermented soy among the foods that harm; choose organic soy).
47. Otun J, Sahebkar A, Östlundh L, Atkin SL, Sathyapalan T. Systematic Review and Meta-analysis on the Effect of Soy on Thyroid Function. Sci Rep. 2019;9(1):3964. doi:10.1038/s41598-019-40647-x
48. Inomata N, Miyakawa M, Aihara M. Surfing as a risk factor for sensitization to poly(γ-glutamic acid) in fermented soybeans, natto, allergy. Allergol Int. 2018;67(3):341-346. doi:10.1016/j.alit.2017.11.001
49. Aoyagi R, Okita K, Uda K, Ikegawa K, Yuza Y, Horikoshi Y. Natto intake is a risk factor of Bacillus subtilis bacteremia among children undergoing chemotherapy for childhood cancer: A case-control study. J Infect Chemother. 2023;29(3):329-332. doi:10.1016/j.jiac.2022.12.010
50. Sada RM, Yamamoto G, Hamaguchi S, Kuroda E, Okura A, Cai M, et al. The Majority of Bacillus subtilis Strains Isolated From Blood Cultures Were Derived From Traditional Japanese Fermented Soybeans Natto: A Single-center Retrospective Study. Open Forum Infect Dis. 2025;12(9):ofaf574. doi:10.1093/ofid/ofaf574
51. Lampe BJ, English JC. Toxicological assessment of nattokinase derived from Bacillus subtilis var. natto. Food Chem Toxicol. 2016;88:87-99. doi:10.1016/j.fct.2015.12.025

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