IGF1 and obesity due to melanocortin 4 receptor deficiency: Indeed, muscle is also source of IGF-1, known to be one of the factors which cooperate in the maintenance of skeletal health [43].In addition, lower levels of IGF-1 [27, 41] have been found in obese individuals (unpublished observation) and IGF-1 might play a pivotal role in the mechanism linking obesity to decreased bone density and bone quality [41], by mechanism due to altered osteoblast homeostasis.