Impact of High-Fat Diet and Aflatoxin B1 on Immunometabolic Dysfunction and the Dose-Responsive Modulation by Isoleucine Supplementation

Objectives: Disruption of gut–liver axis homeostasis is a hallmark of metabolic and toxic stress. This study aimed to evaluate the combined effects of high-fat diet (HFD), aflatoxin B1 (AFB1), and exogenous isoleucine supplementation on immunometabolic function under nutritional and toxic stress. Methods: Two-phase murine experiments assessed: (1) HFD and AFB1 effects individually and combined; and (2) dose-dependent isoleucine responses (25/50/100 mg/kg) across control, HFD, and HFD + AFB1 backgrounds. Results: HFD significantly impaired liver function, promoted Th17-mediated inflammation, and induced gut dysbiosis, while AFB1 alone exerted minimal effects. Their combination synergistically exacerbated hepatic steatosis, intestinal barrier disruption, and inflammatory responses. Fecal metabolomics identified elevated isoleucine as a potential inflammatory biomarker. Under HFD, isoleucine (50 mg/kg) amplified inflammation and oxidative stress. Remarkably, under HFD + AFB1, moderate/high-dose isoleucine reduced hepatic lipid deposition and triglycerides despite persistent intestinal damage, demonstrating context-dependent effects. Conclusions: HFD and AFB1 synergistically disrupt gut–liver axis integrity through immunometabolic mechanisms. Isoleucine supplementation exhibits dual-modulatory effects, exacerbating damage under nutritional stress while partially mitigating hepatic lipid accumulation under combined toxic-nutritional stress, highlighting the critical importance of environmental context in amino acid interventions.