FGF21 and obesity due to melanocortin 4 receptor deficiency: Finally, our findings suggest that n-3 LCPUFA exert their favorable effects counteracting on obesity by targeting distinct pathways, such as PPARα and AMPKα in iBAT, but also in liver and small intestine, thereby increasing energy expenditure, whereby FGF21 as downstream target of PPARs reflects the activation of PPARα by n-3 PUFA and the activation of several downstream signaling pathways including AMPKα [35, 39].