Six months after bariatric surgery, an increase in plasma ANGPTL8 was observed in patients with obesity submitted to sleeve gastrectomy (pre-surgery 9.34 ± 0.94 vs. post-surgery 10.85 ± 1.13 ng/mL, p < 0.05) and RYGB (pre-surgery 20.76 ± 3.53 vs. post-surgery 47.53 ± 5.47 ng/mL, p < 0.001). The gene discussed is ANGPTL8; the disease is obesity due to melanocortin 4 receptor deficiency.