What Is Natto? Japan's Most Polarizing Food Explained

Natto (納豆) is fermented whole soybeans — sticky, ammonia-pungent, intensely savory, divisive. It is, depending on who you ask in Japan, either the most nutritious daily breakfast staple or the most challenging food in Japanese cuisine to adopt.

Even within Japan, natto is regionally divisive: eastern Japan (Tokyo, Tohoku, Kanto) eats natto routinely and proudly; western Japan (Osaka, Kyoto, Kansai region) historically used natto much less and maintains more skepticism. When Japanese people discover someone doesn't eat natto, the first question is always: "Are you from Kansai?"

What Natto Is

Natto is made by fermenting cooked soybeans with Bacillus subtilis var. natto, a bacterium that produces a specific fermentation character: the distinctive stickiness (mucilage — a polysaccharide polymer called poly-gamma-glutamic acid), the strong ammonia-tinged smell, and the deep fermented flavor.

History: Natto has been eaten in Japan for approximately 1,000 years. The most plausible origin story: Buddhist monks accidentally discovered fermented soybeans left in straw, realized they were edible (and delicious), and the tradition spread. Until the 20th century, natto was typically sold wrapped in straw — the straw itself harbored the Bacillus subtilis needed for fermentation. Modern natto uses commercial Bacillus starter cultures and styrofoam packaging.

What Natto Tastes Like

Describing natto to someone who hasn't eaten it is difficult because its flavor components don't map to Western food categories:

The base flavor: Intensely savory, deeply umami, with a strong fermented funk that has ammonia, earthiness, and some sourness. Not as sour as kimchi or strong cheese — more organic and pungent.

The texture: This is where most first-timers struggle. Natto has two texture elements: the beans themselves (firm, slightly waxy) and the coating mucilage (extremely sticky, stretchy, fibrous strings). When stirred, the strings multiply. A single chopstick pull creates elaborate string formations.

Smell: Pronounced. Some describe it as ammonia, others as very strong cheese, others as barnyard. The smell is part of the flavor profile and doesn't necessarily predict the eating experience.

How to Eat Natto

The traditional method:

1. Open the package, which contains the natto beans and small packets of soy sauce and karashi (hot mustard)
2. Mix vigorously with chopsticks — the goal is to develop the sticky strings and aerate the beans. Traditional wisdom says to mix 100 times; practically, mix until the beans are coated with white foam and the strings are well-developed (30-60 seconds)
3. Add the provided soy sauce and mustard. Mix again
4. Add thinly sliced green onion
5. Pour over hot white rice and eat

Variations:

• Kimchi natto: Add a spoonful of kimchi to the natto before mixing — common in Korean-Japanese communities and increasingly popular generally
• Natto with raw egg: A raw egg yolk added to the natto and mixed in — richer, more emulsified
• Natto maki: Natto rolled inside nori and sushi rice. One of the most popular sushi roll types in Japan
• Natto on toast: A distinctly non-traditional but practical way for natto beginners to try it — spread natto on buttered toast with a splash of soy sauce

Nutrition

Natto is one of the more nutritionally dense fermented foods:

Protein: 17-18g per 100g serving — high-quality complete protein from soybeans.

Vitamin K2 (MK-7): Natto is the richest dietary source of vitamin K2 in the form of menaquinone-7 — a form with high bioavailability, associated with bone health and cardiovascular research. A single 50g serving of natto provides far more K2 than any other food.

Nattokinase: An enzyme unique to natto fermentation, studied for potential cardiovascular properties (fibrinolysis). Research is ongoing.

Probiotic bacteria: Live Bacillus subtilis var. natto that survive digestion.

Fiber: High dietary fiber from whole soybeans.

Note for warfarin users: The very high vitamin K2 content in natto can significantly interact with warfarin (blood thinner) therapy. Patients on anticoagulants should discuss natto with their physician.

The East-West Divide

The natto divide in Japan is cultural, not genetic. Eastern Japan (particularly Tohoku and Kanto regions) developed natto eating traditions through centuries of Buddhist temple influence, cold-climate preservation needs, and cultural habit. Osaka and Kansai developed a distinct food identity around different proteins and fermentation styles.

Survey data consistently shows:

• 70-80% of eastern Japanese adults eat natto regularly
• 30-50% of western Japanese adults eat natto at all
• The line runs roughly through the Japanese Alps

Visiting Japan and ordering natto in a Kyoto restaurant will earn you a different reaction than the same order in a Tokyo breakfast diner.

For First-Time Natto Eaters

Recommendations:

1. Try it in natto maki first — the rice and nori moderate the experience
2. Use the full mustard packet — the heat helps
3. Mix thoroughly before adding soy sauce
4. Eat it while both the natto and rice are at temperature — cold natto is more challenging
5. Don't smell it too deliberately before eating — approach it as breakfast food, not as a challenge

The acquired nature of natto appreciation is genuine — most non-Japanese people who adopt natto eating report that it took 3-5 tries before the flavor profile clicked. It's worth the effort: there are very few foods that provide this nutritional profile in this form.

Related reading: Traditional Japanese Breakfast Guide | History of Japanese Cuisine | Japanese Fermented Foods Guide