Gut microbiota involvement in the effect of water-soluble dietary fiber on fatty liver and fibrosis

The beneficial effects of water-soluble dietary fiber on liver fat and fibrosis involve the gut microbiota; however, few epidemiological studies have investigated this association. This large-scale epidemiological study aimed to determine the effect of water-soluble dietary fiber intake on liver fat and fibrosis via gut microbiota for the general population. We divided low- and high-intake groups by median daily water-soluble dietary fiber intake and matched background factors by propensity score matching for sex and age. The high-intake group had lower controlled attenuation parameters, a lower fatty liver index, and a lower mac-2-binding protein glycosylated isomer level than the low-intake group. Furthermore, in the high-intake group, the prevalences of metabolic dysfunction-associated steatotic liver disease and cardiometabolic criteria were significantly lower than in the low-intake group. In the high-intake group, there were increases and decreases in 16 bacterial species. Of them, those belonging to Faecalibacterium and Gemmiger had higher relative abundances than the other species and had a negative correlation with the fatty liver index and its components triglyceride and glutamyl transpeptidase in a multivariate analysis adjusted for confounding factors. On the other hand, Dorea showed a significant negative correlation with liver stiffness measure, even though Dorea was decreased in the high-intake group. Faecalibacterium and Gemmiger are butyrate-producing bacteria, suggesting that water-soluble dietary fiber may inhibit fatty liver via gut butyric acid production.