Objective This study explored how dietary rhythms influence metabolic-associated fatty liver disease (MAFLD) progression and the interactions among the circadian gene Bmal1, the gut microbiota, and MAFLD.

Methods Male Wistar rats were divided into five groups to simulate dietary rhythm disruptions: Control (ad libitum access to the high-fat diet), Control-T, ABX, ABX-FMT, and ABX-B (high-fat diet only during the rest phase). After 17 weeks, the ABX, ABX-FMT, and ABX-B groups received antibiotics to deplete gut microbiota, then ABX-FMT and ABX-B groups followed by fecal microbiota transplantation (FMT) from MAFLD patients or Bifidobacterium longum supplementation for 4 weeks, respectively. Metabolic function and MAFLD phenotypes were assessed via physiological measurement and histopathological methods. The expression of gene Bmal1 was evaluated via RT-qPCR and immunohistochemistry, while changes in the gut microbiota were detected by 16S rDNA amplicon sequencing.

Results Compared with the free-feeding Control group, diet rhythm-disrupted rats (Control-T group) showed aggravated hepatic injury, with elevated serum ALT and AST, increased steatosis and inflammation on HE staining, and downregulated hepatic Bmal1 expression. Antibiotic-mediated microbiota depletion (ABX group) markedly altered microbial abundance versus the Control-T group, attenuating hepatic inflammation and steatosis while upregulating Bmal1. Fecal microbiota transplantation from MAFLD patients (ABX-FMT group) increased serum ALT/AST and decreased Bmal1 relative to the ABX group, with reduced phylum-level Firmicutes abundance. Supplementation with Bifidobacterium longum (ABX-B group) alleviated hepatic steatosis and inflammation, lowered ALT/AST and NAS scores, upregulated Bmal1, and increased Verrucomicrobiota while decreasing Firmicutes, Desulfobacterota, and Proteobacteria.

Conclusion Dietary rhythm disruption may be associated with aggravated liver inflammation and steatosis, linked to abnormal expression of the liver circadian gene Bmal1. The gut microbiome may play a crucial role in regulating liver circadian gene expression and metabolic processes through dietary rhythm signals, and probiotic supplementation could help alleviate MAFLD lesions, accompanied by restoration of liver circadian genes and metabolic homeostasis.