Zucker Fatty (ZF) rats with a leptin receptor defect exhibit obesity, insulin resistance with hyperinsulinemia and normal glycemia that progress to type 2 diabetes in 6–12 weeks (4); ZF rats have severe mitochondrial inhibition with low oxidation of palmitic acid to CO2[30]. The gene discussed is LEPR; the disease is obesity due to melanocortin 4 receptor deficiency.