GHRL and obesity due to melanocortin 4 receptor deficiency: According to the study by Singhal V et al., one year after sleeve gastrectomy, fasting serum ghrelin levels in patients with obesity remained significantly lower, with a concentration of 36.0 ± 8.3 pg/ml, compared to 247.0 ± 35.5 pg/ml in the non-surgical control group (p < 0.0001) [43].A prospective cohort study conducted by Ozmen et al. demonstrated that patients with obesity who underwent sleeve gastrectomy achieved significant weight loss one year after surgery.