PPARD and obesity due to melanocortin 4 receptor deficiency: Interestingly, we have found recently that supplementation of L-carnitine to obese rats counteracts the obesity-induced muscle fiber transition from type I to type II through inducing genes encoding critical molecular regulators of muscle fiber transition, like peroxisome proliferator-activated receptor δ (PPARδ encoded by PPARD), PPARγ coactivator-1α (PGC-1α encoded by PPARGC1A) and PGC-1β (PPARGC1B) [9–12], and thereby favours an oxidative metabolic phenotype of skeletal muscle [13].