LEP and obesity due to melanocortin 4 receptor deficiency: Furthermore, studies on leptin in both animal and human have shown that obesity is generally associated with elevated leptin levels [17], whereas leptin is said to play a dual role of inhibition/stimulation of lipogenesis and lipolysis, respectively, reducing intracellular lipid levels in skeletal muscle, liver, and pancreatic beta cells, thereby improving insulin sensitivity [18].