Subjects carrying the Val/Val genotype of the UCP2 Ala55Val polymorphism appear to have a lower degree of uncoupling of the mitochondrial internal membrane, lower energy expenditure [50], higher exercise energy efficiency [51], higher metabolic rate, increased susceptibility to obesity and T2DM [16], [45], [52], [53] and greater weight loss [54] than subjects with the Ala allele. Here, UCP2 is linked to obesity due to melanocortin 4 receptor deficiency.