TNF and obesity due to melanocortin 4 receptor deficiency: Obesity is associated with elevations in insulin, free insulin-like growth factors (IGFs), and adipocyte-derived factors that include leptin, tumor necrosis factor-alpha (TNF-α), interleukin (IL) 6, and reductions in adiponectin [5]. Several theories have been proposed to explain the association between elevated BMI and postoperative complications.