IGF1 and obesity due to melanocortin 4 receptor deficiency: Collectively, it may be hypothesized that obesity induces feedback inhibition of pituitary GH secretion by increasing non-fasting serum FFA levels and the associated insulin resistance that causes compensatory intra-portal hyperinsulinemia and IGFBP-1 suppression, with the net result being low GH and normal IGF-I levels.