FFAR2 and Crohn disease: To further explore the clinical implication of key components of this EGCG-regulated multilevel intestinal microecosystem, we first analyzed the enrichment of fecal SCFAs, including propionic acid, butyric acid, and valerate/isovalerate, and the gene expression of colon epithelial FFAR2 in primary patients with Crohn's disease (CD) or Ulcerative colitis (UC) using a public database (untargeted metabolic data from Project ID PR000639 in the Metabolomics Workbench (http://www.metabolomicsworkbench.org); bulk RNA-seq data are from GSE111889) [24].