LEP and obesity due to melanocortin 4 receptor deficiency: Peripheral administration of exogenous leptin results in a specific reduction in body fat mass with no change in lean mass in experimental animals [39] or in obese humans on a weight-reducing diet [40], but elevated concentrations of endogenous leptin do not appear to be capable of preventing, or reversing, the accumulation of adipose tissue during, or after, the development of obesity [41].