FGF21 and obesity due to melanocortin 4 receptor deficiency: Circulating serum FGF-19 concentrations were similarly lower (p < 0.01) in individuals with obesity, regardless of their degree of insulin resistance, while FGF-21 levels were higher in individuals with obesity (p < 0.01), and further increased in obesity-associated T2D (p < 0.01) compared to healthy controls.