In all patients with obesity, glucose levels during meal test correlated significantly with duodenal GLP‐1 cell numbers (0 min: r = 0.388, p = 0.048; 30 min: r = 0.330, p = 0.086; 60 min: r = 0.456, p = 0.048; 120 min: r = 0.370, p = 0.058, AUC r = 0.405, p = 0.048; incremental AUC r = 0.399, p = 0.048), but among the subgroups of patients with or without T2D or in the controls, no significant correlations emerged. This evidence concerns the gene GCG and obesity due to melanocortin 4 receptor deficiency.