Soy, Vitamin K2 and Natto

Andrea Fabry

Andrea Fabry › Andrea is a former journalist, a radio host, and the mother of nine children. She is ...


January 6th is National Bean Day, which begs the question, “Should we celebrate the soybean?”

The problem with soy in its natural state is that it contains various anti-nutrients that present problems for the immune system.These anti-nutrients help protect the bean from the sun’s radiation and microbial invasion, but work against the people interested in consuming soy.

Soy’s anti-nutrients:

Phytates:  All beans contain phytates (or phytic acid). Soaking typically removes most of this, but soybeans are particularly stubborn in this regard. Fermentation offers an extra boost.

Enzyme inhibitors: Enzymes digest our food. When enzyme inhibitors are present, enzymes can’t do their job. This leads to gas and bloating, as well as a host of other issues. Soaking usually solves this, but again the fermentation helps the process along.

Goitrogens: These substances potentially block production of thyroid hormones. Fermentation does not eliminate goitrogens. Because the sugar separates from the goitrogens during fermentation, goitrogens may actually be increased. A healthy thyroid should handle this, however some suggest using alternate beans, such as navy beans. Others suggest consuming foods high in iodine to counter the goitrogen effect. Still others suggest keeping fermented soy consumption to a minimum. Certainly less may be more when it come to fermented soy.

Should we celebrate the soybean?

Why pay tribute to the fermented soybean then?

Because fermented soy  in forms such as tempeh, miso and natto offer unique health benefits. Natto, in particular, is rich in vitamin K2, a fat soluble vitamin closely connected with the health of our bones, teeth and overall immune system.

The health benefits of vitamin K2

  • Protects against heart disease
  • Helps ensure healthy skin
  • Contributes to strong bones
  • Promotes brain function
  • Supports growth and development
  • Fights against cancer

To learn more about the immune boosting properties of vitamn K2, I recommend the book,Vitamin K2 and the Calcium Paradox. Author Kate Reheaume-Bleue offers an excellent explanation of why calcium supplements are coming up short in the fight against osteoporosis and why adult women are in need of vitamin K2.

While vitamin K2 is a recent discovery, it’s important to note that researcher Dr. Weston Price became aware of  its benefits while studying dental health and diet in the 1930’s. Dr. Price found that primitive people groups with the healthiest teeth consumed traditional foods rich in a mystery compound he termed Activator X. We now know it as vitamin K2. (For more on Dr. Price’s research see On the Trail of the Elusive X-factor: A Sixty-Two-Year-Old Mystery Finally Solved.)

Convinced about vitamin K2? Look what natto has to offer!

       Data taken from the book Vitamin K2 and The Calcium Paradox p. 66


*The butter in this graph refers to standard butter rather than butter from cows raised on fast growing grasses. The egg yolk statistic does not reflect pastured chickens raised in the outdoors. In both cases, vitamin K2 levels would be higher, but not nearly as high as natto.

Want to add natto to your diet? Here are some options:

Store-bought natto.

Most Asian markets carry natto in their frozen food section. The flavor packets contain numerous additives. These can easily be tossed. The natto in the styrofoam package typically has lots of strings, which indicates proper fermentation. It is not clear whether or not the soybeans have been genetically modified.

Natto in supplement form. 

Vitamin K2 comes from two sources: animal and bacteria. The  K2 found in grass-fed meat, egg yolks and butter is called menaquinone-4 or MK-4. If this appears on the label it is likely synthetic. Vitamin K2 in bacterial form has a range of MK-5 through MK-10. MK-7 is the one found in natto, and the one you’ll typically see on supplement labels. Amazon offers these varieties of vitamin K2 supplements.

Homemade natto.

Making natto from scratch is not as hard as it may seem. One of the biggest benefits is quality control. There are a number of farms that offer organic, non-GMO soybeans:

Laura Soybeans
Bob’s Red Mill
Wheatgrass kits

I have been making my own natto for 2 years, and have found a method that works for me. The recipe is outlined here. I did not acquire the taste easily. Once I did, I found myself craving it. I’ll typically have several spoonfuls daily along with a calcium supplement I make with dried eggshells.

See more on the interplay between calcium and vitamin K2 in the article What You Need to Know About Vitamin K2, D and Calcium.

Ready to celebrate National Bean Day? Why not try natto?

This article originally appeared on It is reproduced here with permission.

Tell us how you feel about soy.

Photo credit: Andrea Fabry