For evaluating whether the magnitude of RYGB surgery-induced weight loss after two years is related with pre-surgery 25-OH-vitamin D status (< 50 nmol/L equals deficiency) and FTO genotype, Bandstein et al. examined the role of 25-OH-vitamin D and FTO in the weight loss effect of RYGB surgery in obese patients [30]. Here, FTO is linked to hyperinsulinemic hypoglycemia, familial, 4.