STAT3 and overnutrition: Although it is well known that some of the molecular mechanisms leading to insulin and leptin resistance involve alterations in key molecules of their intracellular signaling pathways, such as signal transducer and activator of transcription 3 (STAT3), suppressor of cytokine signaling 3 (SOCS3) and protein tyrosine phosphatase 1B (PTP1B) [12],[14],[15], why and how central insulin and leptin resistance are induced by overnutrition is not completely understood.