For instance, study populations with obesity class 1 (BMI 30–34.9 kg/m2) and class 3 (BMI ≥ 40 kg/m2) are afflicted differently by hyperinsulinemia, hyperleptinemia, insulin and leptin resistance or low ghrelin levels [22,23]. Here, GHRL is linked to obesity due to melanocortin 4 receptor deficiency.