The gut and liver talk to each other more than most of us realize. What happens during digestion can affect more than the stomach. It may also shape how the body handles fat, blood sugar and inflammation.
A small human study from the University of Jyväskylä in Finland adds to that growing area of research. Scientists studied a daily prebiotic fiber supplement called xylo-oligosaccharides, or XOS, in 42 adults with overweight. Participants took 2.8 grams per day for four months, and researchers used MRI scans to measure liver fat before and after the study.
The findings, published in npj Gut and Liver, do not show that XOS is a proven treatment for fatty liver disease. The study was small, and the researchers said larger studies are needed. But the results suggest that the gut may help explain why some people benefit more than others from certain nutrition changes.
The study focused on metabolic dysfunction-associated steatotic liver disease, or MASLD, a condition many people know as fatty liver disease. It is linked to overweight, obesity, insulin resistance and type 2 diabetes risk. If it worsens, it can contribute to more serious liver disease.
Lifestyle changes remain the main treatment approach, but they can be difficult to maintain. That has led researchers to study whether supporting the gut microbiome, the community of bacteria and other microbes living in the digestive tract, could also help.
Prebiotics are a type of fiber that feed beneficial gut bacteria. Unlike some nutrients that are absorbed earlier in digestion, prebiotic fibers travel to the colon, where gut bacteria break them down.
In this study, researchers found that XOS appeared to reduce certain gut byproducts that have been linked to liver fat buildup. In simpler terms, the supplement may have helped shift what gut bacteria were producing during digestion.
“Our findings suggest that, when applied to the right target group, XOS can restore gut fermentation balance, reduce the production of harmful metabolites, and thereby benefit liver health,” said Jukka Hintikka, the study’s first author.
That phrase “the right target group” is important. The supplement did not appear to work the same way for everyone.
Researchers saw the strongest effects in people whose gut bacteria seemed more out of balance at the start of the study. In those participants, XOS appeared to shift the gut in a healthier direction. Researchers also observed a reduction in visceral fat, the deeper abdominal fat that surrounds internal organs.
The effects were weaker, or not seen, in participants whose blood markers suggested more advanced fatty liver disease.
That does not mean people should rush to buy XOS supplements or order gut microbiome tests. It does suggest that future treatments for fatty liver may become more personalized, with researchers paying closer attention to how a person’s gut health affects their response.
The study also shows why fiber advice can be both useful and incomplete. Eating more fiber is generally linked to better health, but not all fibers act the same way in the body. A supplement is also not the same as an overall eating pattern built around fiber-rich foods such as beans, vegetables, fruits, whole grains, nuts and seeds.
“In the future, our findings may contribute to the development of personalized treatments for fatty liver disease,” Hintikka said. “However, larger and more targeted studies are still needed to confirm these results.”
That caveat matters. This study points to a possible path for future research, not a ready-made supplement solution.
The study was funded by an Academy Research Fellow grant awarded to Satu Pekkala.