INS and obesity due to melanocortin 4 receptor deficiency: Obese individuals have elevated levels of circulating free fatty acids (FFAs) [49,50], which is thought to be due to (1) a surplus of metabolically active FFA-secreting adipocytes and (2) due to a vicious cycle of obesity-associated insulin resistance; insulin normally inhibits FFA mobilization from adipocytes, but excess of visceral adipose tissue is associated with insulin resistance [51].