Lactobacillus fermented carambola juice alleviates HFD-induced obesity and insulin resistance by modulating the gut microbiota and PPARγ signaling pathway

Dietary supplementation with carambola juice has shown notable effects on obesity. However, the mechanism by which fermented carambola juice (FCJ) alleviates insulin resistance in obesity induced by high-fat diet (HFD) is unclear. This study aimed to evaluate the effects of FCJ on obesity-related biomarkers, glucose homeostasis, and gut microbiota dysregulation in mice on a HFD. The results indicated that both unfermented carambola juice (UCJ) and FCJ reduced body weight, lipid accumulation, and insulin resistance in HFD mice. However, FCJ intervention had significantly stronger effects than UCJ, particularly in reducing lipid accumulation and PPARγ pathway-related proteins expression. Transcriptomic analysis revealed that FCJ modulated the expression of mRNA involved in hepatic glucose and lipid metabolism, primarily enriching the PPARγ pathway, which was confirmed by RT-PCR and western blotting. 16S rRNA analysis showed that UCJ and FCJ restored gut microbiota balance in HFD mice. FCJ increased short-chain fatty acid-producing microbiota and reduced pathogenic microbiota. Notably, FCJ intervention specifically promoted the abundance of Bifidobacterium and Norank_f_Muribaculaceae and enhanced short-chain fatty acid production, whereas UCJ primarily increased Roseburia and Alloprevotella abundance. These findings suggest that FCJ may be a promising functional food for managing obesity and insulin resistance.