GCG and obesity due to melanocortin 4 receptor deficiency: In humans and rodents, GLP‐1 levels are reduced in obesity, while bariatric surgery dramatically increases post‐prandial levels of GLP‐1 (Chambers et al., 2014; Jiménez et al., 2014; Umeda et al., 2011) as early as a few days after the surgery (Le Roux et al., 2007).