The supplementation of BCAA will lead to the proliferation of R. flavefaciens which synthesized and released acetic acid into the portal vein, so that the expression of fatty-acid synthase (FAS) and acetyl-CoA carboxylase (ACC) in the liver is downregulated, reducing the occurrence of non-alcoholic fatty liver disease (NAFLD) (30). Here, FAS is linked to metabolic dysfunction-associated steatotic liver disease.