T2DM: Type 2 Diabetes Mellitus; FBG: Fasting Blood Glucose; EGCG: Epigallocatechin-3-Gallate; TCM: Traditional Chinese Medicine; DHA: Docosahexaenoic Acid; EPA: Eicosapentaenoic Acid; BCAA: Branched Chain Amino Acids; GLP-1: Glucagon Like Peptide 1; ImP: Imidazole Propionate; MAPK: Mitogen-Activated Protein Kinase; SCFA: Short-Chain Fatty Acid; HOMA-IR: Homeostatic Model Assessment for Insulin Resistance; VLDL: Very Low Density Lipoprotein; ROS: Reactive Oxygen Species; MICT: Moderate-Intensity Continuous Training; PRISMA: Preferred Reporting Items for Systematic reviews and Meta-Analyses. This evidence concerns the gene GCG and diabetes mellitus.