Natto: The Japanese Superfood Most Americans Have Never Tried

Natto is a traditional Japanese food made from fermented soybeans. It is one of the most nutrient-dense foods in the Japanese diet, has an exceptionally strong research base for cardiovascular benefits through its primary active compound nattokinase, and contains the highest known food source of vitamin K2 MK-7. It is also one of the most challenging foods for Western palates, with a sticky, stringy texture, pungent smell, and intense umami flavor that requires genuine culinary courage to approach for the first time.

NUTRITIONAL PROFILE OF NATTO

A 100-gram serving of natto provides approximately 18 grams of protein, 11 grams of fat, 12 grams of carbohydrates, 5 grams of fiber, and an extraordinary micronutrient profile. It is the richest known food source of vitamin K2 MK-7, with approximately 1000 micrograms per 100g. For context, the recommended daily adequate intake for vitamin K2 is 45 micrograms for adults. Research published in the Journal of Nutrition documented natto as containing concentrations of MK-7 far exceeding any other food source and showed direct correlation between MK-7 levels and bone density in Japanese women.

Beyond vitamin K2, natto provides significant iron, calcium, potassium, copper, manganese, and magnesium. The fermentation process increases the bioavailability of many of these minerals by breaking down phytates that would otherwise bind them. Natto’s complete amino acid profile from whole soybeans combined with the enzymatic breakdown of fermentation makes its protein highly digestible.

NATTOKINASE AND CARDIOVASCULAR HEALTH

Nattokinase is a serine protease enzyme produced during the fermentation of soybeans by Bacillus subtilis natto. It has documented fibrinolytic activity, meaning it breaks down fibrin, the protein matrix of blood clots. Multiple clinical studies have found nattokinase supplementation reduces blood viscosity, fibrinogen levels, and certain cardiovascular risk markers. A systematic review in the Scientific Reports found consistent evidence for cardiovascular benefit from nattokinase.

Important note: people taking blood-thinning medications including warfarin, aspirin, and newer anticoagulants should consult their physician before consuming natto regularly, as the nattokinase activity and vitamin K2 content both interact with anticoagulation therapy.

HOW TO EAT NATTO

Traditional natto consumption in Japan involves stirring the natto vigorously (the stirring develops the characteristic stringy texture further), then eating it over warm rice with toppings including soy sauce, mustard, and chopped green onions. The pungency and texture are significant barriers for non-Japanese consumers. Practical strategies for approaching natto include: starting with small amounts mixed into other strongly flavored foods, using it in fried rice where the flavors integrate, adding it to miso soup, or consuming it cold (many people find the flavor less intense cold than warm).

Frozen natto is available at most Asian grocery stores across the US and is nutritionally equivalent to fresh. It comes in small individual servings (typically 45 to 50 grams per package) that make portion control simple. For athletes building high-protein meal routines, natto is a uniquely dense protein source that also provides probiotic benefit from the live Bacillus subtilis cultures it contains.

VITAMIN K2: WHY IT MATTERS

Vitamin K2 directs calcium to bones and away from arteries. Deficiency is associated with arterial calcification and reduced bone density. Most Western diets are significantly deficient in K2 because fermented foods containing it (natto, aged cheeses, fermented soy) are not dietary staples. The Japanese population consumes K2 at levels far exceeding Western populations, largely through natto, and has significantly lower rates of hip fracture and osteoporosis than countries with comparable dairy intake.

INTRODUCING NATTO TO YOUR DIET GRADUALLY

The most common approach for natto-curious people who are hesitant about the flavor and texture is to start with natto incorporated into other dishes rather than eating it plain. Natto fried rice is one of the most accessible preparations: the frying process integrates the natto into the rice, reducing the stringiness and distributing the flavor throughout the dish. Natto mixed into miso soup is another entry point where the strong flavors of the broth moderate the pungency of the natto. Natto toast with avocado and soy sauce is a modern fusion preparation that works surprisingly well and has become popular in Japanese-Western fusion contexts.

Give yourself 3 to 5 exposures to natto before deciding whether you like it. First exposure is almost always challenging regardless of how adventurous an eater you are. By the third or fourth experience, many people report that they have genuinely acquired the taste. The nutritional benefits, particularly the extraordinary vitamin K2 and nattokinase content, justify the investment in adaptation. Even small amounts of natto (one package of 50g, 2 to 3 times per week) provide meaningful cardiovascular and bone health benefits, so you do not need to eat it daily to access its key benefits.

The probiotic content of natto from Bacillus subtilis var. natto is distinct from the probiotic strains in yogurt and kefir. Consuming diverse fermented foods exposes the gut to different microbial species, and the Bacillus subtilis in natto has documented immune-modulating properties not shared by Lactobacillus-dominant fermented dairy. For people already incorporating fermented dairy and vegetables in their diet, adding natto once or twice per week expands the microbial diversity contribution of dietary fermented foods.

Natto is available at most Japanese and Korean grocery stores across the US and increasingly at Whole Foods and other natural food retailers in areas with substantial Asian populations. It is sold frozen in packages of 3 individual servings (typically 45 to 50 grams each), thaws in the refrigerator overnight, and has a refrigerated shelf life after thawing of 3 to 5 days. The per-serving cost is approximately $1.50 to $3 depending on brand and retailer, making it one of the most affordable high-nutrient-density foods available. For athletes tracking protein per dollar spent, natto provides approximately 9 grams of complete protein per serving at a cost that competes favorably with most other protein sources.

A critical note for people taking warfarin or other vitamin K-antagonist blood thinners: natto’s extraordinary vitamin K2 content (approximately 500 micrograms per 45g serving) dramatically affects anticoagulation stability. Consuming even a single serving of natto can significantly elevate INR for several days. People on warfarin should not consume natto without coordinating with their prescribing physician and possibly adjusting their warfarin dose accordingly.

FREQUENTLY ASKED QUESTIONS

Does natto taste good?

Natto has an acquired taste that many non-Japanese people find challenging on first exposure. The sticky texture, pungent smell, and intense umami are unlike most Western foods. Most people who eat it regularly develop genuine appreciation for it, particularly over rice with soy sauce and mustard.

Can I take nattokinase supplements instead of eating natto?

Yes. Nattokinase supplements are widely available and provide the enzyme without the challenging texture and flavor of natto. They are appropriate for people who want the cardiovascular benefits without eating the food. People on anticoagulant medications should consult their physician before using nattokinase supplements.

Is natto safe to eat every day?

Yes for most people. Traditional Japanese consumption is daily. The high vitamin K2 content makes it important for people on warfarin to consult their physician, as K2 affects anticoagulation.