FGF21 and type 2 diabetes mellitus: T2DM: type 2 diabetes mellitus; FPG: fasting plasma glucose; HOMA-IR: homeostatic model assessment for insulin resistance; FGF-21: fibroblast growth factor-21; IL-6: interleukin 6; TNF-α: tumor necrosis factor alpha; Hs-CRP: high-sensitivity C-reactive protein; MDA: malondialdehyde; TAOS: total antioxidant status