Fatty liver disease is not some rare condition.

Metabolic dysfunction-associated fatty liver disease (MASLD) affects roughly 25-30% of adults worldwide. It used to be called “NAFLD (non-alcoholic fatty liver disease),” but the name was standardized to MASLD in 2023.

In Japan too, it’s becoming increasingly common among middle-aged and older adults. Left unchecked, it can progress to cirrhosis or liver cancer.

In February 2026, a review article published in Nutrients (MDPI), a leading nutrition journal, brought together what we know about the relationship between fermented foods and the gut-liver axis in a systematic way.

Understanding the “Gut-Liver Axis”

The gut and liver are directly connected by a blood vessel called the portal vein. Everything absorbed in the intestines reaches the liver first. This intimate relationship is called the “Gut-Liver Axis.”

When things are healthy, the intestinal barrier keeps harmful substances out. But when gut bacteria fall out of balance, something called “leaky gut” develops, and bacterial toxins (LPS) flow through the portal vein straight into the liver.

This triggers inflammation in the liver and promotes fat accumulation, leading to MASLD progression. A damaged gut isn’t just a gut problem—it’s a whole-body issue.

Three Pathways Through Which Fermented Foods Influence the Gut-Liver Axis

The paper identifies three mechanisms by which fermented foods work on the gut-liver axis to protect the liver.

Production of Short-Chain Fatty Acids (SCFAs)

Beneficial bacteria in the gut produce short-chain fatty acids—acetate, propionate, and butyrate—which nourish the intestinal epithelial cells while strengthening the intestinal barrier. By protecting the gut wall, they prevent toxins from leaking into the liver.

Normalization of the Gut Microbiota

Beneficial bacteria found in fermented foods—like Lactobacillus (lactic acid bacteria) and Bifidobacterium—suppress pathogenic bacteria and balance the microbial ecosystem. This keeps LPS-producing bacteria from proliferating, reducing the inflammatory signals that reach the liver.

Adjustment of Bile Acid Metabolism

Bile acids synthesized in the liver are converted by gut bacteria into secondary bile acids. Through this process, energy and lipid metabolism are regulated. Improved gut microbiota from fermented foods is thought to optimize this bile acid metabolism as well.

What Clinical Trials Show

The paper references several clinical studies.

In one trial with 80 MASLD patients, a group that consumed kefir (a fermented milk drink) for eight weeks showed increased HDL cholesterol (the “good” kind) and decreased systemic inflammation (Mohammadi et al.).

Research by Wastyk et al. at Stanford University (published in Cell in 2021) is also cited, showing that people who consumed more fermented foods had greater gut bacterial diversity and a reduction in 19 inflammatory proteins.

Both findings support the idea that regularly eating fermented foods improves gut health and reduces inflammatory signals to the liver.

Connection to Japanese Fermented Foods

Among the fermented foods mentioned in the paper are yogurt, kefir, kimchi, and tempeh—alongside miso and amazake (sweet fermented rice).

Japanese traditional fermented foods align perfectly with this category of foods that influence the gut-liver axis.

Miso, in particular, is a complex fermented food created through the combined work of lactic acid bacteria, yeast, and koji mold. From the perspective of supporting beneficial gut bacteria, promoting short-chain fatty acid production, and maintaining intestinal barrier function, it’s a food worthy of attention in the context of MASLD prevention.

In Summary

Fermented foods show promise in balancing gut microbiota and slowing MASLD progression through the gut-liver axis. The mechanism operates through three pathways: short-chain fatty acid production, normalization of gut bacteria, and adjustment of bile acid metabolism.

The paper itself notes that “larger, longer-term clinical trials are needed,” so we’re still at the stage of “promising possibility” rather than proven fact. Even so, the reality that daily fermented food consumption can influence both gut and liver health offers an important perspective for thinking about diet.

Caring for your gut is caring for your liver. When you look at it that way, the meaning of fermented foods deepens a little.

---

The gut and liver are connected. What we eat, day after day, keeps that axis in balance.

---

From Toshi

I’ve loved alcohol since I was young.

I’ve had many wonderful times because of it. At the same time, I pushed myself a bit too hard sometimes, and my body paid the price.

If I could tell my younger self what I know now… I found myself thinking about that while reading this article.

The idea of the “gut-liver axis”—that the gut and liver are connected. The simple fact that whatever you eat or drink goes straight to your liver.

It seems obvious now, but back then, it felt like distant knowledge.

I knew fermented foods were good for you. I did know that. But I never really thought deeply about why.

What struck me this time was the thought: “Maybe all those years, the foods I ate were quietly protecting my liver without me realizing it.” But at the same time, there were also things I couldn’t protect.

If I’d understood the gut-liver axis back then, maybe I would have made different choices.

I feel a little regret about that. But I also know it’s not too late to understand it now.

Simply adding miso and fermented foods to my daily meals. Nothing fancy—just consistency.

That’s what will protect my body going forward.

I think it could be a helpful insight for anyone who loves drinking as much as I do.

Caring for your gut means protecting your liver.

With that thought, I want to keep tending to my table, day after day.

※ 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.