PPARD and obesity due to melanocortin 4 receptor deficiency: Ligand-activated PPARβ/δ could increase the levels of serum high-density lipoprotein cholesterol, decrease the levels of serum triglycerides in mice [60], non-human primates [62], and humans [120], and improve the metabolic syndrome such as obesity and insulin resistance induced by a high-fat diet or genetic predisposition [116,121].