Notably, fructose-stimulated FGF21 levels were shown to be increased in adults with metabolic syndrome compared to healthy participants (4), and plasma FGF21 levels following glucose administration were found to be higher in people with obesity compared to healthy-weight (6), suggesting that metabolic impairments affect carbohydrate-induced FGF21 secretion. Here, FGF21 is linked to obesity due to melanocortin 4 receptor deficiency.