Together, these data support our observation that BMI only partially mediates the FGF19–diabetes association and highlight the need for future longitudinal and mechanistic studies integrating bile acid metabolomics (total and individual bile acids), FXR/TGR5 pathway biomarkers, gut microbiome features, and comprehensive inflammatory profiling to delineate causal pathways and identify potential therapeutic targets. This evidence concerns the gene NR1H4 and diabetes mellitus.