FGF21 and obesity due to melanocortin 4 receptor deficiency: This study, therefore, aimed to investigate if (1) FGF21 is associated with sweet food and taste preference in patients with severe obesity scheduled for bariatric surgery, (2) bariatric surgery leads to changes in FGF21 and (3) if altered FGF21 levels are associated with changes in sweet food and taste preferences following bariatric surgery.