One of the most studied traditional fermented foods on the planet. Here is everything the research says about natto, nattokinase, and why vitamin K2 MK-7 from this single food stands apart from every other source.
Natto is a traditional Japanese food made from whole soybeans fermented with Bacillus subtilis var. natto. The fermentation process transforms the soybean's nutrient profile dramatically — producing nattokinase (a serine protease with fibrinolytic properties), vitamin K2 in the MK-7 form, free amino acids, and a characteristic sticky, stringy matrix of poly-γ-glutamic acid.
The flavor is polarizing: pungent, ammonia-edged, deeply savory. The texture is slimy and cohesive. In Japan, natto is eaten at breakfast over rice with soy sauce, mustard, and chopped green onion. Outside Japan, it is increasingly sought for its biochemical profile rather than tradition — and for good reason.
Japan, estimated over 1,000 years of documented use. Produced commercially since the early 20th century using pure B. subtilis starter cultures.
Nattokinase enzyme, vitamin K2 MK-7, poly-γ-glutamic acid, dipicolinic acid, free isoflavones, complete protein, menaquinone-7.
Fresh natto contains approximately 1,000 fibrinolysis units (FU) per gram — among the highest enzymatic activity of any commercially available fermented food.
Natto contains 775–1,000 mcg of vitamin K2 MK-7 per 100g — orders of magnitude more than dairy, meat, or fermented cheeses.
Nattokinase (NK) was isolated and characterized as a distinct fibrinolytic enzyme in 1987 by Dr. Hiroyuki Sumi at the University of Chicago. The enzyme belongs to the subtilisin family of serine proteases and has demonstrated the ability to directly degrade fibrin — the protein meshwork of blood clots — without requiring plasminogen as an intermediary.
This direct fibrinolytic mechanism distinguishes nattokinase from most endogenous fibrinolytic enzymes, which typically work through plasminogen activation cascades. Research has continued to accumulate on NK's cardiovascular effects, including blood pressure modulation and platelet aggregation.
Sumi et al. (1987) identified nattokinase as a potent fibrinolytic enzyme extracted from natto. In this landmark study, NK degraded fibrin clots more effectively than plasmin over a comparable 18-hour incubation period, with the enzyme showing robust activity in standard blood clot dissolution assays. This paper established NK as a novel food-derived enzyme with cardiovascular research potential.
Atsumi et al. (2018) conducted a randomized controlled trial examining nattokinase supplementation's effects on cardiovascular risk markers in human participants. The study found statistically significant reductions in LDL cholesterol, total cholesterol, and lipoprotein(a) — Lp(a) — a particularly difficult-to-modify independent cardiovascular risk factor. The trial used a standardized nattokinase extract over a 26-week intervention period.
Schurgers and Vermeer (2000) conducted a critical comparative study of menaquinone forms, demonstrating that MK-7 (found in natto) has dramatically superior bioavailability and half-life compared to MK-4 (found in animal products). MK-7 demonstrated a serum half-life of approximately 3 days versus MK-4's near-undetectable half-life of hours, meaning a single serving of natto sustains carboxylation of K-dependent proteins far longer than any other dietary source.
The Rotterdam Study, one of the largest prospective cohort studies on vitamin K2 and cardiovascular outcomes, followed 4,807 participants and found that higher dietary intake of menaquinones (K2) was significantly associated with reduced all-cause mortality, cardiovascular mortality, and severe aortic calcification. The association was specific to menaquinones, not phylloquinone (K1), underscoring the unique role of MK-7 from fermented foods like natto.
Vitamin K2 MK-7 activates two critical proteins in the body: osteocalcin (which binds calcium to bone matrix) and matrix Gla protein (which inhibits soft tissue calcification). When K2 is deficient, calcium tends to deposit in arterial walls rather than bone — a dynamic that epidemiological data links to both osteoporosis and atherosclerosis simultaneously.
Natto's K2 MK-7 concentration is extraordinary. A single 100g serving provides 775–1,000 mcg — well above the adequate intake of 120 mcg/day for adults and sufficient to fully saturate K2-dependent carboxylation for several days. No other food comes close. Aged cheeses like Gouda and Brie contain 50–75 mcg per 100g. Chicken liver contains approximately 35 mcg. Natto is in a category of its own.
Important note for anticoagulant users: The high K2 content in natto can interfere with warfarin (Coumadin) therapy. Individuals on anticoagulation must consult their physician before adding natto to their diet. This is a pharmacologically meaningful interaction.
Home natto fermentation requires only three things: soybeans, Bacillus subtilis starter culture, and a way to hold a stable 40°C (104°F) temperature for 22–24 hours. The process is straightforward once you understand the environmental requirements of B. subtilis — it thrives in warm, humid, oxygen-present conditions and outcompetes nearly all pathogens at fermentation temperature when given a head start with quality starter.
Natto's flavor has been described as earthy, nutty, savory, and intensely umami — with an ammonia back-note that fades after the first few bites. The texture is uniquely sticky; pulling beans apart with chopsticks produces long filaments of poly-γ-glutamic acid.
Traditional Japanese preparation: one pack of natto stirred vigorously 30–40 times with the included soy sauce and mustard packets, then poured over steamed rice. The stirring intensifies the string formation and is considered integral to proper preparation.
Western-friendly approaches for beginners: mix into avocado toast, blend into miso soup (the miso flavor complements it strongly), or fold into fried rice where the other flavors moderate the natto's intensity. Once accustomed, the flavor is often craved — it occupies the same deeply savory register as aged cheese or marmite.
Where to buy: Japanese grocery stores stock natto reliably. The frozen section typically carries Okame brand, the most recognized commercial product. Online specialty retailers carry artisanal natto from small Japanese producers. If fresh natto is unavailable, nattokinase supplements and vitamin K2 MK-7 supplements offer targeted delivery of the specific compounds.
Fresh and frozen natto is not universally available, and some individuals cannot tolerate the flavor. Nattokinase supplements and vitamin K2 MK-7 supplements provide the key bioactive compounds in standardized form. Nattokinase supplements are typically dosed at 100 mg (approximately 2,000 FU) per capsule. K2 MK-7 supplements commonly provide 90–200 mcg per serving.
Both are available widely online. When evaluating nattokinase supplements, look for products that specify FU (fibrinolysis units) activity on the label — this is more meaningful than milligram dosage alone. For K2 MK-7, the trans-MK-7 form (sometimes labeled as "all-trans") has stronger documented bioactivity than synthetic cis-MK-7.
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