A study conducted at the University of Jyväskylä, Finland, was the first to investigate the effects of prebiotic xylo-oligosaccharides (XOS) on fatty liver in humans. The findings suggest that the fiber supplement may reduce harmful metabolic byproducts in the gut and thereby improve liver health. Importantly, the composition of the gut microbiota prior to supplementation influences the benefits observed.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a common comorbidity of overweight and obesity, affecting about 75% of individuals with excess weight. If left untreated, the condition may progress to liver cirrhosis or even liver cancer. Lifestyle changes remain the primary treatment approach, but adherence to them is often challenging, highlighting the need for complementary therapies.

Fiber supplement reduced harmful gut metabolites

In the study conducted in the Faculty of Sport and Health Sciences at the University of Jyväskylä, 42 overweight adults consumed 2.8 grams of XOS prebiotic daily for four months. Prebiotics are dietary fibers that are not digested by human enzymes but instead reach the colon, where they support the balance of the gut microbiota. Liver fat content was assessed using magnetic resonance imaging before and after the intervention.

The results showed that XOS reduced the levels of certain harmful amino acid-derived metabolites in the gut, which have previously been linked to liver fat accumulation.

“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,” says Jukka Hintikka, the first author of the study.

Baseline gut microbiota influenced response to intervention

The prebiotic appeared to be most effective in individuals with an initially imbalanced gut microbiota. These individuals showed signs of increased protein fermentation relative to carbohydrate fermentation in the gut. XOS supplementation helped rebalance microbial composition. In this subgroup, a reduction in visceral fat was also observed.

In contrast, the effect of the prebiotic was weaker, or not observed at all, in participants whose blood markers suggested more advanced stages of fatty liver disease.

This study is the first clinical trial in humans to examine the effects of XOS prebiotics on liver fat. The findings are consistent with earlier animal studies, in which XOS reduced fatty liver in rats.

“In the future, our findings may contribute to the development of personalized treatments for fatty liver disease,” says Hintikka. “However, larger and more targeted studies are still needed to confirm these results.”

The study was published in npj Gut and Liver.

The study was funded by an Academy Research Fellow grant awarded to Satu Pekkala.