I started noticing my cholesterol levels once I hit my 50s.

At every health checkup, I’d hear the same thing: “Could you bring it down a bit more?” That’s when I decided to change my diet and turned to fermented foods. Shio koji, soy koji, nukadoko (rice bran for pickling), miso—before I knew it, I was eating something made with koji almost every single day.

Then I came across some research about koji and cholesterol.

In a clinical trial, cholesterol dropped 21mg/dL

This comes from a clinical study published in Clinical Nutrition back in 2015.

Patients with high cholesterol were given koji-fermented foods for 12 weeks, and their total cholesterol dropped an average of 21mg/dL. Twelve weeks, and 21 points. When you look at the numbers, that’s a pretty solid change.

And there’s more—another study from 2021 confirmed that a group consuming fermented soy products for 12 weeks saw total cholesterol drop by 0.23 mmol/L, with LDL (the “bad” cholesterol) dropping 0.18 mmol/L.

The enzymes created by koji quietly work inside your body

Koji mold (Aspergillus oryzae) produces hundreds of different enzymes.

Protease (breaks down protein), amylase (breaks down starch), lipase (breaks down fat). These work inside your gut and help balance your intestinal bacteria. Research shows they’re particularly good at helping Bifidobacterium species multiply.

There’s invisible work happening inside your stomach. When I think about it that way, my daily shio koji and pickled vegetables start to look different.

Everything I use every day is actually koji-made

When I really think about it, almost everything fermented on my table comes from koji.

Miso (soybeans + koji), shio koji (brown rice koji + salt), soy koji (brown rice koji + soy sauce). Every meal means miso soup, pickled vegetables in the bran. Even the homemade miso I put down in winter. It’s all fermented by the power of koji mold.

By the way, koji mold is recognized by the FDA (U.S. Food and Drug Administration) as “Generally Recognized As Safe (GRAS).” It’s got the official stamp of approval for safety too.

From “restriction” to “restoration”—what fermented foods changed for me

When I was chasing those cholesterol numbers, I think I was stuck in a “depriving myself” mindset. Cut the oil, hold back on the things I love. It was subtraction, not addition.

But after I started eating fermented foods, something shifted. Instead of restricting, it became more about “restoring balance.” A spoonful of shio koji, a bowl of miso soup, some pickled vegetables on the side. Just that, and my whole meal would feel more balanced and nourishing.

To be honest, I didn’t feel dramatic changes right away. But as I kept going, there was this quiet sense of my body getting sorted out from the inside. The way I wake up in the morning, how light I feel after eating. Those small changes that don’t show up on a number sheet kept adding up.

Seeing these research results now, it feels like my gut feeling got backed up by science. When I think about that 21mg/dL number and imagine there are others quietly accumulating those same small changes, it feels a little more reassuring.

I don’t think I’ll do anything different going forward. I’ll keep making miso soup the way I always do, keep putting my hands in the nukadoko. But I want to do it with awareness that each one of these small acts is quietly restoring balance in my body.

Fermentation isn’t something you “use”—it’s something you live alongside. That’s how I feel about it now.

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Koji is a mold that Japanese people have carefully cultivated over centuries. And now, science is starting to speak its language.

※ This article is based on personal experience and publicly available information. It is not intended to diagnose, treat, or prevent any disease. If you have health concerns, please consult a doctor or registered dietitian. See our Disclaimer.