A microbiome-brain-β cell axis mediated by acetate promotes metabolic syndrome. Increased gut microbiota-derived acetate activates the parasympathetic nervous system, leading to enhanced glucose-stimulated insulin secretion (GSIS), increased ghrelin secretion, hyperphagia, and obesity. The study shows that altered gut microbiota in high-fat diet (HFD) rats increase acetate production, which in turn activates the parasympathetic nervous system, driving GSIS and metabolic syndrome. Whole-body acetate turnover was significantly increased in HFD rats, with acetate primarily produced in the gut microbiota. In vitro experiments confirmed that fecal microbes generate acetate from glucose and fatty acids, and that antibiotics reduce acetate production. Acetate infusion in chow-fed rats replicated the GSIS increase seen in HFD rats, indicating that acetate turnover drives GSIS. Acetate also increases plasma gastrin, a marker of parasympathetic activation. Vagotomy reduced GSIS, and parasympathetic blockade with atropine prevented acetate-induced GSIS. Intracerebroventricular acetate infusion also increased GSIS, suggesting a central effect. Chronic acetate infusion led to hyperphagia, weight gain, and metabolic syndrome, with parasympathetic activation being essential. Germ-free mice had negligible acetate production, confirming the gut microbiota's role in acetate generation. These findings highlight the gut microbiota-brain-β cell axis as a therapeutic target for obesity and metabolic syndrome.A microbiome-brain-β cell axis mediated by acetate promotes metabolic syndrome. Increased gut microbiota-derived acetate activates the parasympathetic nervous system, leading to enhanced glucose-stimulated insulin secretion (GSIS), increased ghrelin secretion, hyperphagia, and obesity. The study shows that altered gut microbiota in high-fat diet (HFD) rats increase acetate production, which in turn activates the parasympathetic nervous system, driving GSIS and metabolic syndrome. Whole-body acetate turnover was significantly increased in HFD rats, with acetate primarily produced in the gut microbiota. In vitro experiments confirmed that fecal microbes generate acetate from glucose and fatty acids, and that antibiotics reduce acetate production. Acetate infusion in chow-fed rats replicated the GSIS increase seen in HFD rats, indicating that acetate turnover drives GSIS. Acetate also increases plasma gastrin, a marker of parasympathetic activation. Vagotomy reduced GSIS, and parasympathetic blockade with atropine prevented acetate-induced GSIS. Intracerebroventricular acetate infusion also increased GSIS, suggesting a central effect. Chronic acetate infusion led to hyperphagia, weight gain, and metabolic syndrome, with parasympathetic activation being essential. Germ-free mice had negligible acetate production, confirming the gut microbiota's role in acetate generation. These findings highlight the gut microbiota-brain-β cell axis as a therapeutic target for obesity and metabolic syndrome.