As you know if you've been following this blog for a while, obesity risk has a strong genetic component . Genome-wide association studies (GWAS) attempt to identify the specific locations of genetic differences (single-nucleotide polymorphisms or SNPs) that are associated with a particular trait. In the case of obesity, GWAS studies have had limited success in identifying obesity-associated genes. However, one cluster of SNPs consistently show up at the top of the list in these studies: those that are near the gene FTO. As with many of the genes in our genome, different people carry different versions of FTO. People with two copies of the "fat" version of the FTO SNPs average about 7 pounds (3 kg) heavier than people with two copies of the "thin" version, and they also tend to eat more calories ( 1 , 2 ). Despite being the most consistent hit in these genetic studies, FTO has remained a mystery. As with most obesity-associated genes, it's expressed in...