Probiotics fail to reduce leaky gut in fatty liver disease, RCT finds

Not every gut-health study delivers a win for the supplement being tested, and that is exactly the value of this one. A double-blind, placebo-controlled randomized clinical trial in adults with biopsy-confirmed metabolic dysfunction-associated steatohepatitis (MASH, a more advanced, inflamed form of fatty liver disease) tested whether a probiotic supplement could tighten a leaky gut. After 24 weeks, the probiotic group looked no different from the placebo group. It is a clean, well-controlled null result, and a useful check on the assumption that any probiotic will fix gut-barrier problems in liver disease.

Key takeaways

• In a 24-week randomized trial in adults with biopsy-confirmed MASH (a severe form of fatty liver disease), a probiotic supplement was no better than placebo at lowering claudin-3, a blood marker of gut permeability.
• Levels of claudin-3 dropped significantly in both groups, probiotic and placebo alike, and the drop tracked with an unplanned, roughly equal reduction in calorie intake in both groups, not with which sachet participants took.
• Probiotics are not proven to fix gut-barrier problems in fatty liver disease based on this trial; the improvement seen appears to trace back to participants eating less during the study, a common effect of simply being monitored.

Probiotic Supplement Showed No Advantage Over Placebo for Gut Permeability in MASH

Researchers at Universidade Federal do Rio Grande do Sul in Brazil ran a secondary analysis of a randomized, double-blind, placebo-controlled trial in adult outpatients with liver biopsy-confirmed MASH. Forty-six patients were randomized to receive either a four-strain probiotic mixture (Lactobacillus acidophilus, L. rhamnosus, L. paracasei, and Bifidobacterium animalis subsp. lactis) or a matching placebo, twice daily for 24 weeks; 44 completed the trial. The researchers tracked serum claudin-3, a blood protein that leaks out when the tight junctions sealing the intestinal wall together break down, as a stand-in for how permeable, or "leaky," the gut had become. Before treatment, claudin-3 levels were similar in both groups. After 24 weeks, claudin-3 fell from a baseline of 14.7 ng/mL to 6.1 ng/mL in the probiotic group and from 16.7 ng/mL to 6.0 ng/mL in the placebo group, a difference the researchers found was not statistically meaningful between groups.

Why This Matters for Anyone With Fatty Liver Disease Considering a Probiotic

MASH is a progressive form of fatty liver disease tied to intestinal permeability: when the gut barrier weakens, bacterial byproducts can leak into the bloodstream and travel to the liver, where they help drive the inflammation and injury that define the disease. That biological link has made "fix the gut, help the liver" an appealing pitch for probiotic supplements, and broader research on the gut-liver axis in fatty liver disease supports the idea that gut barrier health matters for liver outcomes generally. This trial specifically targeted people already living with a confirmed, biopsy-proven diagnosis of MASH, not a healthy population or an animal model, which is exactly the group any real-world probiotic recommendation would target. The result, that a well-characterized four-strain probiotic did not outperform placebo on this measure, is a meaningful data point against assuming any probiotic will meaningfully repair a leaky gut once fatty liver disease has progressed this far.

A Randomized, Double-Blind Design Makes the Null Result Credible

What makes this result worth taking seriously rather than dismissing as a failed trial is the design behind it. This was a randomized, double-blind, placebo-controlled trial, the strongest available design for testing whether a supplement actually works, with both patients and researchers unaware of who received the real probiotic until after the data were analyzed. The placebo itself was a matched sachet designed to look and taste like the probiotic mixture. Compliance was high in both arms, and the two groups did not differ meaningfully in baseline characteristics like age, body mass index, diabetes, or hypertension rates. Critically, the researchers also tracked dietary intake throughout the trial and found that both groups reduced their calorie, carbohydrate, protein, and fat intake by similar, statistically significant amounts, even though participants were explicitly told not to change their diet. That unplanned dietary shift, likely a byproduct of the increased attention and self-monitoring that comes with being in a trial, lines up closely with the claudin-3 drop seen in both groups, giving the researchers a plausible alternative explanation for the improvement that has nothing to do with probiotics.

What This Means If You Have Fatty Liver Disease

If you have MASH, or a fatty liver diagnosis more broadly, and were considering a probiotic specifically to help a "leaky gut," this trial's result suggests you should not expect it to move that specific marker on its own. The researchers found that reducing calorie and macronutrient intake, something that happened unintentionally in this trial simply from being monitored, tracked with the improvement in gut-permeability markers regardless of which sachet a participant took. That points toward diet and monitoring, not a specific probiotic strain combination, as the more plausible driver worth discussing with a doctor or dietitian if gut-barrier health in liver disease is a concern. This is not evidence that probiotics are harmful or useless for other conditions, only that this trial did not find an added benefit for this specific marker in this specific patient group.

Limitations Worth Knowing

Claudin-3 itself is an "emerging," not fully validated, biomarker for intestinal permeability, since there is no accepted normal reference range for it yet, and the researchers relied on it as their only permeability measure rather than combining it with other established tests like the lactulose-mannitol ratio. The patients in this trial had relatively low-severity MASH with limited fibrosis, so the results may not extend to more advanced liver disease. This was also a secondary analysis of a trial originally designed and powered to study liver histology and cardiovascular markers, not gut permeability specifically, which limits how much weight the specific permeability findings can carry on their own.

What Comes Next

The authors call for longer-term studies to validate claudin-3 as a reliable intestinal-permeability marker in liver disease, potentially paired with more established permeability tests. They also flag that the unintentional dietary changes seen in both study arms deserve dedicated follow-up, since this and prior similarly designed trials in liver disease suggest supervised weight loss or dietary change, rather than probiotic supplementation alone, may be the more promising lever for gut-barrier health in this population.

Common Questions

What is claudin-3 and why does it matter? It is a protein that helps seal the junctions between intestinal cells together. When those junctions break down, more claudin-3 leaks into the bloodstream, so blood levels are used as an indirect signal of how permeable, or "leaky," the gut has become.

Does this mean probiotics don't work for gut health? No. This trial tested one specific four-strain probiotic mixture against one specific blood marker in people with an advanced fatty liver condition; it does not rule out benefits from probiotics for other conditions or other measures of gut health, and other trials on the broader relationship between the gut microbiome and fatty liver disease continue to explore different angles.

Why did the placebo group improve too? Both groups unintentionally reduced their calorie and macronutrient intake over the 24-week trial, likely because being monitored in a study tends to change behavior, and that dietary shift lined up with the improvement in gut-permeability markers in both arms.

Should someone with fatty liver disease still take a probiotic? This trial does not establish that probiotics help repair gut permeability in MASH, so anyone considering one for that specific reason should talk to their doctor about the evidence, or lack of it, rather than assuming it will help.

References

1. Bruna Concheski de Moura, Samanta Catherine Ferreira, Amanda Souza Silva‐Sperb, et al. (2026). Probiotics and intestinal permeability in adults with metabolic dysfunction‐associated steatohepatitis: A secondary analysis of a randomized clinical trial. Journal of Parenteral and Enteral Nutrition. https://doi.org/10.1002/jpen.70144
2. Jingjing Liu, Mei Zhao, Shujing Wang, Chengyong Zhang, Yingli Zhong, Yuanjun Qu (2026). Gut microbiota and the gut–liver axis in MASLD: mechanisms, immune regulation and therapeutic opportunities. Frontiers in Pharmacology. https://doi.org/10.3389/fphar.2026.1917467
3. Ankita Dua, Rashmi Kumari, Mona Singh, et al. (2025). Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD): the interplay of gut microbiome, insulin resistance, and diabetes. Frontiers in Medicine. https://doi.org/10.3389/fmed.2025.1618275