FGF21 and obesity due to melanocortin 4 receptor deficiency: Meta-analyses of GWASs for macronutrient intake (i.e., protein, carbohydrate and fat intake) have confirmed associations between consumption of carbohydrates, fat and protein with the fibroblast growth factor 21 (FGF21) gene and associations of consumption of protein intake with the fat mass and an obesity-associated locus (FTO)10–12.