This study is the first to identify the effects of FTO genotype on the interactions between the level of macro-nutrients intake and the expression level of fat mass and obesity associated (FTO) and homeobox transcription factor iriquois-3 (IRX3) genes This longitudinal study was carried out on 84 overweight and obese adolescent boys in Tehran, Iran. The gene discussed is FTO; the disease is obesity due to melanocortin 4 receptor deficiency.