As expected, leptin and body fat were elevated in participants with obesity before surgery, and decreased significantly post-surgery [% body fat: t(13) = 9.9, P < 0.001; kilogram body fat: t(13) = 13.7, P < 0.001; ng/ml leptin: t(13) = 5.6, P < 0.001; two-tailed, paired t-test; Table 1]. This evidence concerns the gene LEP and obesity due to melanocortin 4 receptor deficiency.