Structural Insights and Metabolic Profiles of Oxidized Green Coffee Extract, and Its Impact on Obesity and Gut Microbiota in High-Fat Diet-Fed Mice

Background: Obesity is a severe chronic disease impacting health, closely linked to intestinal microbiota. Gut microbiome significantly contributes to obesity and metabolic issues. This study aims to explore the structural characterization of two coffee extracts and their effects on gut microbiota disturbances caused by a high-fat diet (HFD). Methods: Male C57BL/6J mice were divided into four groups—normal diet (ND), high-fat diet (HFD), HFD supplemented with unroasted coffee extract (UC), and HFD supplemented with oxidized green coffee extract (GCE). Results: Structural characterization revealed that both extracts are polymeric phenolic compounds rich in hydroxyl and carboxyl groups. Full-target metabolomic analysis revealed significant metabolic differences between the extracts, with 499 differential metabolites identified: a total of 247 metabolites were upregulated and 252 were downregulated in GCE compared to UC. Supplementation with GCE reduced body weight gain and adipose tissue accumulation, improved dyslipidemia and insulin sensitivity, and enhanced hepatic antioxidant capacity in high-fat model mice. Gut microbial analysis showed that GCE significantly (p < 0.05) increased the growth of beneficial bacteria such as Prevotella, Butyricimonas, and Parabacteroides. Conclusions: Oxidized green coffee extract has the effect of lowering lipids and increasing intestinal beneficial bacteria.