Adipocytes of patients with obesity have a lower insulin receptor density and a higher density of beta-3 adrenergic receptors, thus increasing the lipolysis rate with release of FFA, a situation that has several metabolic consequences in which the following are present: increase in the production of oxygen-derived free radicals; induction of insulin resistance; synergism in the action of IL-6 and TNF-α, and induction of apoptosis in pancreatic beta cells; taken together, these effects are categorized as lipotoxicity. Here, TNF is linked to obesity due to melanocortin 4 receptor deficiency.