Recent reports have suggested that suppression of obesity and insulin resistance by atRA is largely mediated by PPARβ/δ [23], and this effect is enhanced by activation of retinoic acid receptors (RAR's), while others have reported that atRA does not compete with established PPARβ/δ agonists in ligand binding assays [24]. This evidence concerns the gene PPARD and obesity due to melanocortin 4 receptor deficiency.