Therefore, in this review our aim is to bring all IGF-1 information regarding metabolism together with the objective of offering clear insight into the issue—this way clarifying how miss-regulation of the GH/IGF-1/insulin axis can lead to metabolic disorders such as MetS and diabetes; introducing how obesity and insulin resistance (initiating factors for the onset of MetS and diabetes) may be opposed by recombinant-human-IGF-1 (rhIGF-1) treatment. The gene discussed is GH1; the disease is obesity due to melanocortin 4 receptor deficiency.