JAPAN

The Nutrient That Tells Calcium Where to Go
is fermented into a soybean dish most Westerners refuse to eat.

Natto  ·  Menaquinone-7 (MK-7)  ·  Mechanism: vitamin K-dependent protein carboxylation

Natto is a traditional Japanese food made from whole soybeans fermented with Bacillus subtilis var. natto. It has been part of the Japanese diet for over a thousand years.

The texture is viscous and stringy, threaded with long pale strands when lifted with chopsticks. The smell is sharp, close to ammonia, which has made natto one of the most polarizing foods in the world.

In the Kantō and Tōhoku regions of eastern Japan, natto is eaten almost daily, typically served cold over steamed rice with soy sauce and a small packet of karashi mustard. It is a breakfast food, not a delicacy.

Even within Japan, the dish divides the population. Western Japan has historically eaten far less of it, and younger generations increasingly pass, but in the regions where the tradition holds, the preparation has not changed in centuries.

What distinguishes natto from every other fermented food is not the probiotics. It is that Bacillus subtilis fermentation produces the highest known dietary concentration of vitamin K2 in the menaquinone-7 form, commonly called MK-7.

Vitamin K is not one nutrient. K1, abundant in leafy greens, handles blood clotting, but K2 activates a separate class of vitamin K-dependent proteins with an entirely different job.

The two that matter most are osteocalcin, which binds calcium into bone, and matrix Gla protein, which prevents calcium from depositing in arterial walls. Without sufficient K2 to carboxylate them, both proteins remain inactive.

The practical consequence is what researchers have called the calcium paradox. Calcium enters the body through food and supplements, but without the activated proteins to route it, the mineral may bypass bone and settle in soft tissue, including the walls of arteries.

America spent decades telling women over fifty to take calcium for their bones. It rarely mentioned the nutrient that routes calcium once it arrives.

In a double-blind, placebo-controlled trial published in Thrombosis and Haemostasis, Knapen and colleagues gave 244 healthy postmenopausal women either 180 micrograms of MK-7 or placebo daily for three years. The MK-7 group showed statistically significant improvement in arterial stiffness, assessed by carotid-femoral pulse wave velocity.

MK-7 has a half-life of roughly seventy-two hours, compared to just one to two hours for the shorter-chain MK-4 found in egg yolks and butter. That longer duration allows it to accumulate in tissue at doses achievable from a single daily serving of fermented soy.

One hundred grams of natto delivers roughly 1,000 micrograms of MK-7, more than five times the dose used in that trial. For most Western adults eating no fermented soy, daily MK-7 intake is near zero.

The how-to

This requires no cooking and takes under five minutes, but it does take one trip to an Asian grocery store or one online order.

Look for natto in the frozen or refrigerated section at Asian grocery stores such as H Mart, Mitsuwa, or Nijiya. Some Whole Foods locations carry it, and it is available from online specialty retailers. A three-pack of single-serve containers typically costs two to four dollars.
Thaw one container overnight in the refrigerator. Open it, stir the beans vigorously with chopsticks or a fork for about thirty seconds until thick strings form, then add the included sauce packets or a small splash of soy sauce.
Eat it over a bowl of warm rice. If the texture is difficult at first, mix it thoroughly into the rice rather than placing it on top. Some people add a soft-cooked egg, sliced scallions, or a drop of sesame oil.
One single-serve pack, roughly forty to fifty grams, already provides several hundred micrograms of MK-7, well above the 180-microgram daily dose used in the Knapen trial.
If you take warfarin or another vitamin K-dependent blood thinner, do not add natto to your diet without consulting your doctor first. The K2 content is high enough to interfere with anticoagulant dosing. Soy allergy is also a contraindication.

Tomorrow: Indonesia and the fresh turmeric tonic Javanese women have prepared daily for centuries.
What changes when you grind the root fresh instead of scooping the powder.

See you then.