This study investigated the gut microbiome and metabolite signatures associated with fibrosis severity in non-obese individuals with nonalcoholic fatty liver disease (NAFLD). Using 16S rRNA sequencing and an independent Western cohort for validation, researchers found significant microbiome diversity alterations linked to fibrosis severity in non-obese, but not obese, subjects. *Ruminococcaceae* and *Veillonellaceae* were prominently associated with fibrosis in non-obese individuals. Stool bile acids and propionate were elevated in this group. Metagenomic sequencing and mouse NAFLD models further explored the role of specific bacteria, revealing *Ruminococcus faecis* as having a potentially protective effect on fibrosis. The study suggests potential microbiome-based markers for diagnosing fibrosis in non-obese NAFLD.

Giljae Lee, Hyun Ju You, Jasmohan S. Bajaj, Sae Kyung Joo, Junsun Yu, Seoyeon Park, Hyena Kang, Jeong Hwan Park, Jung Ho Kim, Dong Hyeon Lee, Seonhwa Lee, Won Kim, GwangPyo Ko