Polysaccharides are widely present in herbs with multiple activities,especially immunity regulation and metabolic benefits for metabolic disorders.However,the underlying mechanisms are not well under-stood.Functional metabolomics is increasingly used to investigate systemic effects on the host by iden-tifying metabolites with particular functions.This study explores the mechanisms underlying the metabolic benefits of Astragalus polysaccharides(APS)by adopting a functional metabolomics strategy.The effects of APS were determined in eight-week high-fat diet(HFD)-fed obese mice.Then,gas chromatography-time-of-flight mass spectrometry(GC-TOFMS)-based untargeted metabolomics was performed for an analysis of serum and liver tissues,and liquid chromatography-tandem mass spectrom-etry(LC-MS/MS)-based targeted metabolomics was performed.The potential functions of the metabo-lites were tested with in vitro and in vivo models of metabolic disorders.Our results first confirmed the metabolic benefits of APS in obese mice.Then,metabolomics analysis revealed that APS supplemen-tation reversed the HFD-induced metabolic changes,and identified 2-hydroxybutyric acid(2-HB)as a potential functional metabolite for APS activity that was significantly decreased by a HFD and reversed by APS.Further study indicated that 2-HB inhibited oleic acid(OA)-induced triglyceride(TG)accumula-tion.It was also found to stimulate the expression of proteins in lipid degradation in hepatocytes and TG lipolysis in 3T3-L1 cells.Moreover,it was found to reduce serum TG and regulate the proteins involved in lipid degradation in high-fat and high-sucrose(HFHS)-fed mice.In conclusion,our study demonstrates that the metabolic benefits of APS are at least partially due to 2-HB generation,which modulated lipid metabolism both in vitro and in vivo.Our results also highlight that functional metabolomics is practical for investigating the mechanism underlying the systemic benefits of plant polvsaccharides.