rs9939609

rs9939609 is a non-coding variant in the first intron of FTO on chromosome 16 and one of the most replicated common markers associated with body weight. In European adult cohorts, each A allele was associated with about 0.36 kg/m2 higher BMI and roughly 1.2 kg higher average body weight. Small controlled meal studies linked A-carrier genotypes to feeling less full or having a weaker drop in hunger after eating, but they did not measure how soon hunger returned and their samples were small. A meta-analysis of 9,563 adults in eight randomized trials found that this marker did not change response to diet, exercise, or drug-based weight-loss programs. The causal mechanism is not settled, and this exact marker does not carry the same validated BMI meaning in African-ancestry populations.