Obesity runs in families, with parents with higher body mass indexes (BMIs) tending to have children with higher BMIs. This familial transmission is in part because of genetic influences—that is, the heritability of obesity.1 That childhood obesity is heritable is a very reliable and robust finding, with heritability estimates (ie, the percentage of variance in BMI attributable to genetics) generally falling in the range of 60% to 85%.2 That genes have an important impact on childhood obesity would surprise few pediatricians or parents. Likewise, few would disagree.