The purpose of this research is to determine the role of CYP2B6 in PUFA metabolism and test whether CYP2B6 is an anti-obesity enzyme by comparing diet-induced obesity (DIO) between Cyp2b-null mice and our newly produced humanized CYP2B6 mice to determine if human CYP2B6 can reverse obesity and NAFLD in Cyp2b-null mice. This evidence concerns the gene CYP2B6 and obesity due to melanocortin 4 receptor deficiency.