Stinky, Slimy and Stringy, but the Healthiest Soy Food Ever

There’s nothing natty about natto. This old-fashioned soy product is made from whole soybeans that have been soaked, boiled or steamed, and then fermented.    It’s known for its sticky coat, cheesy texture, musty taste, sliminess, stringiness and pungent odor.   Healthwise, it’s good for us and one of the “good old soys.”

Natto first appeared in northeastern Japan about a thousand years ago.  Traditionally, it smelled like straw because it was made by inoculating whole cooked soybeans with Bacillus subtilis or Bacillus natto and incubated in straw.   The straw also absorbed the none-too-fragrant ammonia-like odor.   Because of frequent contamination by unwanted microorganisms, natto makers abandoned the straw method in favor of inoculating the cooked beans with B. natto, then mixing and packing the product in wooden boxes or polyethylene bags.

Natto is one of the few fermented soy products in which bacteria predominate over the fungi.  It’s made the news as the very best source of vitamin K2.    The runners up are all animal foods such as goose and chicken liver, cheese, egg yolk, bacon and butter.   Natto beats all of them by far  though we can certainly get plenty with a rich and varied WAPF diet containing those foods.

K2 is a fat-soluble vitamin best known for its roles in blood clotting and healthy bone formation and preservation.

There’s only two studies that convincingly suggest soy might prevent osteoporosis, and, unfortunately for the soy industry, the only soy food that seems to do that is natto. The bone building, of course, doesn’t come from the miracle bean itself, but from the vitamin K2 manufactured by the bacteria involved in the fermentation process.   Vitamin K2 is conspicuously absent from tofu, soy milk or  soybean products, and researchers have found no significant or consistent association between their intake and bone mineral density despite the soy industry’s grand hope of finding a bone building elixir in the phytoestrogens.

Natto is also the source for nattokinase, an enzyme sold as a supplement and recommended by many alternative MDs for cardiovascular and circulatory problems.

Ready to try natto for its health benefits?   It’s most often served with mustard and soy sauce, or used in soups and spreads in Japanese cuisine.  But don’t expect it to be widely available in stores here anytime soon.    It’s definitely an acquired taste, and a little goes a long way.   Children love it — not for its strong, rotten flavor — but because its glistening threads can be stretched, making it one of the all-time great play foods.   As for them actually eating it, well, not likely at least not over here.

Indeed, natto isn’t even popular in all parts of Japan.  In areas where it is popular, many restaurants require patrons to sit in a private area so as not to offend other diners with the distinctive smell.   You could say natto is the durian of soy foods, though most people who get past the smell of durian come to love it.    With natto, that’s not often the case.

Why’s that?    I’ll let the irrepressible Anthony Bourdain —  the brave man who willingly eats insects, live cobra and just about everything else —  explain how he was defeated by natto:

“What I was not ready for, and never will be, was natto  .  .  .  an unbelievably foul, rank, slimy, glutenous and stringy goop of fermented soybeans.  . . .  If the taste wasn’t bad enough, there’s the texture.  There’s just no way to eat the stuff.  I dug in my chopsticks and dragged a small bit to my mouth.  Viscous long strands of mucuslike material followed, leaving numerous ugly and unmanageable strands running from my lips to the bowl.  I tried severing the strands with my chopsticks, but to no avail.  I tried rolling them around my sticks like recalcitrant angel-hair pasta.  I tried slurping them in.  But there was no way.  I sat there, these horrible-looking strings extending from mouth to table like a spider’s web, doing my best to choke them down while still smiling . . . All I wanted to do now was hurl myself through the paper walls and straight off the edge of the mountain.   Hopefully, a big tub of boiling bleach or lye would be waiting at the bottom for me to gargle with.”

That about sums it up, but for one thing.   Unlike Vegemite, natto‘s actually very good for you!

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The Whole Soy Story: The Dark Side of America’s Favorite Health Food (New Trends, 2005) Chapter 5: Soybeans with Culture.

A Cooks Tour: Adventures in Extreme Cuisine by Anthony Bourdain (Bloomsbury, 2001).

Ikeda Y, Iki M, Morita A, Kajita E, Kagamimori S, Kagawa Y, Yoneshima H.  Intake of fermented soybeans, natto, is associated with reduced bone loss in postmenopausal women: Japanese Population-Based Osteoporosis (JPOS) Study.   J Nutr. 2006 May;136(5):1323-8.

Fujita Y, Iki M, Tamaki J et al.  Association between vitamin K intake from fermented soybeans, natto, and bone mineral density in elderly Japanese men: the Fujiwara-kyo Osteoporosis Risk in Men (FORMEN) study.  Osteoporos Int. 2012 Feb;23(2):705-14. doi: 10.1007/s00198-011-1594-1.

For more on Vitamin K read “On the Trail of the Elusive X Factor:  A Sixty-Two Year Old Mystery FInally Solved” by Chris Masterjohn as well as other articles by him.

Kaayla T. Daniel, PhD, CCN, is The Naughty NutritionistTM because of her ability to outrageously and humorously debunk nutritional myths. A popular guest on radio and television, she has appeared on The Dr. Oz Show, ABC's View from the Bay, NPR's People's Pharmacy and numerous other shows. Her own radio show, "Naughty Nutrition with Dr. Kaayla Daniel," launches April 2011 on World of Women Radio. Dr. Daniel is the author of The Whole Soy Story: The Dark Side of America's Favorite Health Food, a popular speaker at Wise Traditions and other conferences, and recipient of its 2005 Integrity in Science Award. Her website is and she can be reached at

2 Responses to Stinky, Slimy and Stringy, but the Healthiest Soy Food Ever

  1. Marc says:

    Awesome. This totally validates my experience with natto as well.
    I wrote an article on my natto experience here @

  2. Deborah says:

    So Bordain eats the foulest crap on earth, such as the slimy putrid innards of insects, which Humans are not created to eat, but gets all squeelish over natto vegetable? Give me a break! Okra is just as slimy.

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