GCG and type 2 diabetes mellitus: Abbreviations: AMPK, AMP-activated protein kinase; BMI, body mass index; GIP, gastric inhibitory polypeptide; GLP-1, glucagon-like peptide 1; GSK-3β, glycogen synthase kinase-3β; HbA1c, hemoglobin A1c; HOMA-β, Homeostatic Model Assessment of β-cell Function; HOMA-IR, Homeostatic Model Assessment of Insulin Resistance; PGC-1α, peroxisome proliferator-activated receptor gamma coactivator 1α; RCT, randomized controlled trial; SIRT1, sirtuin 1; T2DM, type 2 diabetes mellitus.