Natto Day (Nattō no Hi)

What Is Natto Day?

Every year on July 10, Japan celebrates "Natto Day" (Nattō no Hi). The date comes from a play on numbers: "na" (7) and "tō" (10) combine to sound like "nattō." The anniversary was first established in 1981 by the Kansai Natto Industry Cooperative Association to promote natto consumption in the Kansai region, where it was still relatively uncommon at the time. In 1992, the National Natto Cooperative Association Federation re-established it as a nationwide anniversary. It's a day to rediscover the nutritional value of natto, a traditional Japanese fermented food, and incorporate it into a healthy diet.

A Fermentation Story Born from Chance

While there are several theories about natto's origins, they're all rooted in the real-life intersection of wild natto bacteria and Japanese daily life.

• Legends involving Prince Shotoku and Minamoto no Yoshiie: According to records and legends from various regions, boiled soybeans wrapped in straw were left to sit, and wild natto bacteria naturally present on the straw multiplied, producing the sticky, stringy natto we know today. This was a natural outcome of an environment where straw (used as horse feed) and boiled beans coexisted.
• The street vendors who fed Edo's mornings: During the Edo period, natto vendors walked the streets each morning, and natto became established as an affordable, protein-rich staple for ordinary people. This cheap, nutrient-dense food was both an economically and nutritionally sound choice for city dwellers at the time.

The Science Behind Natto, the "Ultimate Probiotic"

Natto's reputation as a "superfood" is backed by solid microbiological evidence.

• Nattokinase improves blood flow: The enzyme nattokinase, found in natto's sticky strands, has been shown to directly dissolve blood clots in blood vessels, scientifically supporting healthier blood flow.
• The astonishing survival power of "spores": When conditions become unfavorable, natto bacteria retreat into a tough protective shell called a "spore." These spores can withstand temperatures of 100°C and the strong acidity of stomach acid, allowing the bacteria to reach the intestines alive and activate beneficial gut bacteria — making them an exceptionally resilient probiotic.
• Vitamin K2 for stronger bones: Natto boasts one of the highest vitamin K2 contents of any food. This vitamin activates proteins that help calcium bind to bone, scientifically contributing to the prevention of osteoporosis.

[Scientific illustration of Bacillus subtilis natto producing threads and a diagram showing its impact on intestinal flora]

Fun Facts About Natto

• Why stirring brings out more flavor: Stirring natto brings glutamic acid, an amino acid, to the surface, making it easier for your taste buds to detect umami. For maximum flavor, it's recommended to stir it around 400 times before adding any sauce.
• The white specks that appear after the expiration date: Those white granules sometimes seen in older natto are crystals of the amino acid tyrosine. They don't indicate spoilage — they're a sign of further protein breakdown (aging), which can give the natto a slightly gritty texture.
• Natto bacteria are incredibly competitive: Natto bacteria are extremely good at outcompeting other microbes. Because of this, sake and soy sauce brewers traditionally avoid eating natto during production periods, to prevent accidental contamination of their fermentation processes.
• Polyamines and anti-aging: Natto is rich in polyamines, compounds that have recently drawn attention in aging research for their role in promoting cell turnover and reducing inflammation.
• "Natto" gains recognition abroad: In recent years, natto has been gaining recognition overseas as a valuable protein source for vegetarians and as a source of vitamin K2, with nutritionists abroad taking note. A uniquely Japanese food is now being recognized worldwide as a scientifically backed health food.

Tips for Enjoying Natto Day

• On July 10 (Natto Day), try stirring your natto a bit more than usual — around 400 times is the benchmark. Watching the umami compounds develop can be a small but satisfying way to refresh a body and mind worn down by the new fiscal year.
• Try pairing natto with kimchi or green onions. The lactic acid bacteria in kimchi support the activity of natto bacteria, while compounds in green onions help your body absorb vitamin B1 — a smart food pairing that maximizes nutritional efficiency.
• Share the history of natto with kids or friends. Learning how this fermented food emerged by chance from straw is a fun way to appreciate the hidden power of microorganisms in the natural world.
• Try eating natto in the evening. Since blood clots tend to form during sleep, eating natto at dinner is a well-timed way to take advantage of nattokinase's blood-flow benefits.

The Resilient White Strands Awaken the Life Force Within You, and the Strength of the Earth, Passed Down Through Tradition, Forges an Unbreakable Core for Tomorrow

July 10 is a day to appreciate the immense power packed into each tiny bean. The sticky strands that emerged by chance from a bundle of straw carry within them centuries of wisdom that have sustained the Japanese people. As the new fiscal year wears you down with stress and busyness, today is the day to stir your natto thoroughly and savor its rich umami. Like the resilient bacteria themselves, may you find the strength to thrive in any environment. Carry that resilient spirit with you into a wonderful summer.