Moreover, the anti-obesity effect was absent in GLP-1 receptor null (GLP-1R KO) mice and in mice that received daily intraperitoneal injections of a PYY receptor antagonist, confirming the causal relationship between GLP-1 and PYY on reduction of body fat accumulation and glucose homeostasis (Zhou et al., 2015). Here, GLP1R is linked to obesity due to melanocortin 4 receptor deficiency.