Recent studies have identified several factors released from BAT in response to exercise (237); here we will discuss 2 of these batokines, including 12,13-dihydroxy-9Z-octadecenoic acid (12,13-diHOME) and fibroblast growth factor 21 (FGF21) in the context of exercise and obesity. Here, FGF21 is linked to obesity due to melanocortin 4 receptor deficiency.