The Role of FTO and Vitamin D for the Weight Loss Effect of Roux-en-Y Gastric Bypass Surgery in Obese Patients

A recent study in children demonstrated that the rs9939609 single-nucleotide polymorphism in the fat mass and obesity (FTO) gene influences prospective weight gain, however, only in those who were vitamin D-deficient. If this might also be the case for Roux-en-Y gastric bypass (RYGB), surgery-induced weight loss is however unknown. The objective of this study is to examine if the magnitude of RYGB surgery-induced weight loss after 2 years depends on patients' FTO rs9939609 genotype (i.e., TT, AT, and AA) and presurgery vitamin D status (< 50 nmol/L equals deficiency). Before and at 24 months after RYGB surgery, BMI was measured in 210 obese patients (mean BMI 45 kg/m(2), 72 % females). Serum 25-hydroxyvitamin D3 levels were also repeatedly measured. Following surgery, vitamin D was supplemented. Possible weight loss differences between genotypes were tested with multiple linear regressions. The per-allele effect of each FTO A-allele on excessive BMI loss (EBMIL) was 3 % (P = 0.02). When split by baseline status, the EBMIL of vitamin D-deficient patients carrying AA exceeded that of vitamin D-deficient patients carrying TT by similar to 14 % (P = 0.03). No such genotypic differences were found in patients without presurgery vitamin D deficiency. Post-surgery serum levels of vitamin D did not differ between groups. Our data suggest that presurgery vitamin D levels influence the size of genotype effects of FTO rs9939609 on RYGB surgery-induced weight loss in obese patients.