Heat-Inactivated FRT4 Alleviates Diet-Induced Obesity via Gut-Liver Axis Reprogramming.

Obesity and related metabolic disorders are major global health challenges. Postbiotics, such as heat-inactivated probiotics, have attracted attention for their improved safety, stability, and potential metabolic benefits compared to live probiotics. However, the comparative anti-obesity effects and mechanisms of live versus heat-inactivated FRT4 remain unclear, so this study systematically evaluated their effects and mechanisms in high-fat-diet-induced obese mice. Mice received oral administration of live or heat-inactivated FRT4 (prepared by heating in a water bath at 80 °C for 5 min) for 16 weeks. Comprehensive analyses included metabolic profiling, histological evaluation, serum and liver biomarkers, gut microbiota composition, liver metabolomics, and transcriptomics. Both live and inactivated FRT4 significantly reduced body weight gain, adiposity, hepatic steatosis, and dyslipidemia, with inactivated FRT4 exhibiting comparable or superior efficacy. Notably, inactivated FRT4 restored gut microbiota composition, increased short-chain fatty acid production, and regulated hepatic metabolic pathways. Multi-omics analyses revealed modulation of lipid biosynthesis, amino acid metabolism, and energy utilization pathways. Specifically, the "biosynthesis of unsaturated fatty acids" pathway was downregulated in metabolomics and significantly enriched in transcriptomics, highlighting its central role in FRT4M-mediated metabolic reprogramming. These findings demonstrate that heat-inactivated FRT4 exerts systemic anti-obesity effects via gut-liver axis modulation, supporting its potential as a promising postbiotic intervention for obesity and metabolic dysfunction.