FGF21 and Insulin resistance: Retinol-binding protein 4 (RBP4), α2-macroglobulin (A2M), fetuin A (FETUA), fetuin B (FETUB), hepassocin (FGL1), leukocyte cell–derived chemotaxin 2 (LECT2), and selenoprotein P (SELENOP) are negative regulators of insulin sensitivity, and they will cause insulin resistance, whereas fibroblast growth factor 21 (FGF21), sex hormone–binding globulin (SHBG), adropin, and angiopoietin-like protein 4 (ANGPTL4) are positive regulators (Lai et al., 2008; Meex and Watt, 2017).