How are FTO and blood sugar related?

The FTO gene (fat mass and obesity-associated) is one of the most robustly replicated obesity loci. Variants such as rs9939609 are strongly associated with higher BMI and modestly increased risk of type 2 diabetes in GWAS. The link to blood sugar is largely indirect: the risk allele promotes increased adiposity and altered food intake (preference for energy-dense foods), which can secondarily impair insulin sensitivity and raise fasting glucose. Direct effects on insulin secretion or hepatic glucose production are not well established. Effect sizes are small – most carriers do not develop metabolic disease. Lifestyle factors (diet, physical activity) are far more influential. A single FTO test is not clinically predictive. Evidence: human-strong (GWAS).