Stimulates glucose uptake in differentiated adipocytes via the induction of glucose transporter SLC2A1/GLUT1 expression (but not SLC2A4/GLUT4 expression). Activity probably 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 (By similarity). Most abundantly expressed in the liver, also expressed in the thymus at lower levels (PubMed:10858549, PubMed:30389664). Expressed in skeletal muscle (at protein level). Secreted in plasma (at protein level) (PubMed:30605666). In the liver, down-regulated in postprandial conditions (PubMed:30389664). Up-regulated at the transcriptional level by CREB3L3 (PubMed:30389664). Belongs to the heparin-binding growth factors family.