LPL and obesity due to melanocortin 4 receptor deficiency: Furthermore, knockout mice lacking an inhibitor to lipoprotein lipase, fasting-induced adipose factor (Fiaf), were not protected from dietary-induced obesity, suggesting GF mice are protected from obesity by two independent mechanisms: increased AMPK activity and levels of Fiaf, known to upregulate the peroxisomal proliferator-activated receptor coactivator (PGC-1α) [22].