A 5:2 Intermittent Fasting Regimen Ameliorates High‐Fat Diet‐Induced MASLD‐Associated Skeletal Muscle Impairment in Mice

BACKGROUND: Metabolic dysfunction-associated steatotic liver disease (MASLD) is a highly prevalent chronic liver disorder worldwide. Its pathogenesis is closely linked to high-fat diets (HFDs) and is frequently accompanied by decreased skeletal muscle quality. Although intermittent fasting (IF) has been shown to effectively alleviate hepatic steatosis and inflammation, its impact on skeletal muscle quality remains unclear. METHODS: Eight-week-old male C57BL/6J mice were randomly divided into two groups and fed a normal chow (NC) or 45% HFD for 14 weeks to induce MASLD. Subsequently, the MASLD model mice were subjected to a 5:2 intermittent fasting (IF5:2) regimen for 12 cycles (2 days of fasting per week, with ad libitum HFD feeding on the remaining 5 days). Grip strength, liver weight and quadriceps muscle mass were measured at sacrifice. Serum samples were collected for biochemical analysis and lipopolysaccharide (LPS) measurement. Liver, skeletal muscle and intestinal tissues were harvested for histopathological examination. Faecal samples were analysed by metagenomic sequencing. The mRNA expression of bile acid receptors and inflammatory genes was detected by qRT-PCR. Targeted free fatty acid profiling was performed in liver and skeletal muscle tissues. RESULTS: Compared with the continuous HFD group, the IF5:2 group showed no significant difference in cumulative energy intake but exhibited significantly reduced body weight, as well as alleviated hepatic steatosis and inflammation. IF5:2 significantly increased grip strength and skeletal muscle cross-sectional area and markedly downregulated mRNA expression of inflammation-related genes in muscle tissue. Regarding intestinal barrier function, the IF5:2 group displayed significantly higher mRNA expression of intestinal tight junction-related genes, a thicker colonic wall and lower serum LPS levels compared with the HFD group. Metagenomic analysis suggested that IF5:2 effectively remodelled HFD-induced gut microbiota dysbiosis and significantly enriched beneficial bacteria including Limosilactobacillus reuteri and Faecalibaculum rodentium, accompanied by significant upregulation of microbial secondary bile acid biosynthesis pathways. mRNA expression levels of bile acid receptors and their downstream regulatory genes in the intestine, liver and skeletal muscle were significantly elevated in the IF5:2 group. IF5:2 treatment significantly reduced free fatty acid levels in the liver and skeletal muscle, which were negatively correlated with the gene expression of bile acid-related receptors in these two tissues. CONCLUSIONS: Cyclic IF5:2 effectively ameliorates HFD-induced MASLD and protects against skeletal muscle impairment. It represents a promising dietary intervention with dual beneficial effects on alleviating hepatic steatosis and maintaining skeletal muscle quality.