AHR and nervous system disorder: Butyrate thus modulates AhR activation.49 Binding to Ahr is important in several metabolic and immune processes (Figure 2), allowing the co-existence of gut microbiota and their host.50 The activation (increase) of AhR downregulates intestinal inflammation, alleviating inflammatory bowel diseases (IBD), including Crohn’s disease and ulcerative colitis (UC), but also celiac disease, metabolic syndrome, liver disease, and neurological disease, as summarized in Figure 2.