A High BCAA diet alleviates NAFLD, by inhibiting the tryptophan-ILA-AHR axis and MAPK9-mediated de novo lipogenesis (DNL), promoting ketogenesis and energy metabolism, and activating PPAR-RXR and pexophagy to promote fatty acid β-oxidation. The gene discussed is MAPK9; the disease is metabolic dysfunction-associated steatotic liver disease.