Therefore, the aim of the present study was (a) to analyse the jejunal expression of genes involved in insulin signalling and glucose metabolism pathway in morbidly obese subjects according to the insulin resistance grade and in those treated with metformin, (b) to analyse the association with the change of body mass index (BMI) and insulin resistance of those subjects after bariatric surgery, and (c) to study the effect of insulin, glucose and leptin on the expression of relevant genes. The gene discussed is LEP; the disease is Insulin resistance.