FTO genotype impacts food intake and corticolimbic activation

Background: Variants in the first intron of the fat mass and obesity-associated (FTO) gene increase obesity risk. People with "high-risk" FTO genotypes exhibit preference for high-fat foods, reduced satiety responsiveness, and greater food intake consistent with impaired satiety. Objective: We sought central nervous system mechanisms that might underlie impaired satiety perception in people with a higher risk of obesity based on their FTO genotype. Design: We performed a cross-sectional study in a sample that was enriched for obesity and included 20 higher-risk participants with the AA (risk) genotype at the rs9939609 locus of FTO and 94 lower-risk participants with either the AT or TT genotype. We compared subjective appetite, appetite-regulating hormones, caloric intake at a buffet meal, and brain response to visual food cues in an extended satiety network using functional MRI scans acquired before and after a standardized meal. Results: Higher-risk participants reported less subjective fullness (chi(2) = 7.48, P < 0.01), rated calorie-dense food as more appealing (chi(2) = 3.92, P < 0.05), and consumed similar to 350 more kilocalories than lower-risk participants (beta = 348 kcal, P = 0.03), even after adjusting for fat or lean mass. Premeal, the higher-risk group had greater activation by "fattening" food images (compared with objects) in the medial orbital frontal cortex (beta = 11.6; 95% CI: 1.5, 21.7; P < 0.05). Postmeal, the higher-risk subjects had greater activation by fattening (compared with nonfattening) food cues in the ventral tegmental area/substantia nigra (beta = 12.8; 95% CI: 2.7, 23.0; P < 0.05), amygdala (beta = 10.6; 95% CI: 0.7, 20.5; P < 0.05), and ventral striatum (beta = 6.9; 95% CI: 0.2, 13.7; P < 0.05). Moreover, postmeal activation by fattening food cues within the preselected extended satiety network was positively associated with energy intake at the buffet meal (R-2 = 0.29, P = 0.04) and this relation was particularly strong in the dorsal striatum (R2 = 0.28, P = 0.01), amygdala (R2 = 0.28, P = 0.03), and ventral tegmental area/substantia nigra (R2 = 0.27, P = 0.01). Conclusion: The findings are consistent with a model in which allelic variants in FTO raise obesity risk through impaired central nervous system satiety processing, thereby increasing food intake.