Oat β-glucan prevents high fat diet induced obesity by targeting ileal Farnesoid X receptor-fibroblast growth factor 15 signaling

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Oat β-glucan has demonstrated an anti-obesity effect against high fat diet. However, its precise regulatory mechanism remains unclear. The anti-obesity effect was related to the structural characteristics. In this study, different molecular weight oat β-glucans were investigated, and yeast glucan was taken as the positive control. Compared with the low molecular weight oat β-glucan, the higher molecular weight β-glucan presented a superior anti-obesity effect, which might be attributed to its viscosity and fermentability. Oat β-glucan effectively modulated microbiota in both the large and small intestines. Correlation analysis revealed that ileal bacteria played a more critical role in lipid metabolism. Most bile acids are recycled in the distal ileum, and bile acid metabolism influences lipid metabolism. Consequently, the impact of oat β-glucan on bile acid metabolism was assessed. Oat β-glucan intervention reduced the abundance of Faecalibaculum, while increasing the abundance of Lactobacillus and Bifidobacterium. These microbiota alterations contributed to an increase in 7-ketodeoxycholic acid, which was identified as a Farnesoid X receptor (FXR) antagonist in cell experiments. Inactivation of ileal FXR-fibroblast growth factor 15 (FGF15) signaling by 7-ketodeoxycholic acid led to enhanced bile acid synthesis via the alternative pathway. Furthermore, upregulated cytochrome P450 family 27 subfamily A member 1 (CYP27A1) promoted chenodeoxycholic acid production, which subsequently activated hepatic FXR and further accelerated hepatic lipolysis through the peroxisome proliferator-activated receptor α (PPARα)-carnitine palmitoyltransferase 1 A (CPT1A) pathway. These findings provide new evidence that oat β-glucan exerts anti-obesity effects by modulating bile acid metabolism.