In relation to metabolic effects, an obesogenic diet induces increased liver expression of C3, C5aR, and C5L2 [8, 14, 55], while C3KO, C5aRKO, C5L2KO, and C3aRKO mice are resistant to diet-induced obesity [8, 9, 23, 24, 56]. This evidence concerns the gene C5AR2 and obesity due to melanocortin 4 receptor deficiency.