Can Natto Be Made Without Soybeans? The Surprising Truth Behind This Japanese Superfood

Part 1 of “The Natto Stories” Series
Let’s Start With a Quick Question!

Q： What are the two main ingredients in traditional Japanese natto?

Bacillus subtilis (natto bacteria) and soybeans.

That’s the standard recipe for itohiki natto — the sticky, stringy, and pungent fermented food loved in Japan and gaining fans worldwide for its incredible probiotic benefits. But here’s a question that surprises many

Q： Is It Possible to Make Natto From Beans Other Than Soybeans?

Many health-conscious eaters and food innovators have wondered:

• Can you make natto from lentils or chickpeas?
• What about pinto beans, black beans, or other legumes?
• Are soybeans really necessary?

The short answer: No, at least, not successfully.

Personal Experiment: What Happens When You Use Non-Soy Beans?

Over 30 years ago, as a curious college student, I experimented by trying to ferment various beans with Bacillus subtilis natto. I tested:

• Red beans
• Pinto beans
• Chickpeas
• Lentils
• And more

The result?

No matter the bean variety, the fermentation failed to produce real natto.

Why Soybeans Are Uniquely Suited for Natto Fermentation

Soybeans (Glycine max) belong to the Fabaceae family, Glycine genus, and contain specific nutrients and amino acids that Bacillus subtilis depends on to thrive and ferment.

Other legumes belong to different genera and species, meaning their biological makeup is incompatible. In fact, they may contain compounds that inhibit the growth of B. subtilis or interfere with the fermentation process.

“Soybeans aren’t just convenient — they’re biologically perfect for natto.”

There’s no published research yet to confirm which compounds make soybeans so effective, but decades of industrial experience suggest soy contains unique fermentation-enabling molecules that no other legume offers.

What Happens During Natto Fermentation?

When Bacillus subtilis successfully ferments soybeans, it creates powerful functional ingredients like:

• Nattokinase, a heart-healthy enzyme linked to blood circulation
• Vitamin K2 supports bone health and cardiovascular wellness
• Polyglutamic acid enhances nutrient absorption and hydration

These are the same compounds that make natto one of the most respected functional superfoods in Japan.

A Well-Kept Industry Secret

Many supplement manufacturers use Bacillus subtilis not to make natto, but to extract nattokinase, vitamin K2, and other compounds at scale.

Even in controlled industrial fermentation, soybeans remain the #1 growth medium for B. subtilis. No other bean has proven more effective for consistent, high-quality probiotic production.

A Happy Accident of History

Hundreds of years ago, somewhere in ancient Japan, Bacillus subtilis encountered soybeans, and natto was born.

This chance meeting between microbe and legume led to a health food rich in tradition, taste, and science-backed benefits.

Despite the growing popularity of alternative beans and plant-based innovations, soybeans are still unmatched when it comes to fermenting true, probiotic-rich natto.

Final Thoughts: Stick With Soy for Authentic Natto

If you’re looking for real natto, plenty of Bacillus subtilis var. natto, plus nattokinase and vitamin K2, traditional natto made from soybeans is still the gold standard. Other beans might ferment, but they simply can’t match the benefits, taste, and texture of authentic Japanese natto.

And this is just the beginning.
? In our next article in The Natto Stories series, we’ll explore the science and history behind natto.

Stay tuned, the world of natto is more fascinating than you think.