Our study investigated 18 patients with obesity and T2DM and showed that SG is an effective intervention to improve obesity (body weight, BMI, and waist circumference), insulin intolerance (fasting blood glucose, glycated hemoglobin, C-peptide, and insulin levels and homeostatic model assessment-insulin resistance index), liver functions (alanine aminotransferase and gamma glutamyl transferase levels), lipid profile (triglyceride and high-density lipoprotein cholesterol level) and NAFLD (FLI). This evidence concerns the gene INS and obesity due to melanocortin 4 receptor deficiency.