Stimulates glucose uptake in differentiated adipocytes via the induction of glucose transporter SLC2A1/GLUT1 expression (but not SLC2A4/GLUT4 expression). Activity requires the presence of KLB. Regulates systemic glucose homeostasis and insulin sensitivity. Interacts (via C-terminus) with KLB; this interaction is direct. Interacts with FGFR4. Belongs to the heparin-binding growth factors family.