Among the genes correlated to obesity, the FTO (or fat mass gene) is one of the genes responsible for the accumulation of fat in humans. "Each copy of the mutation of this gene is associated with an increase of 3.3 lbs. This means that people who have two copies can weigh 6.6 lbs more than those who have no copies."But "its effect practically disappears among adolescents who perform the daily recommended amount of physical activity," which is an hour or so a day during adolescence. This is another reason for real gym class in middle schools.
People with one allele of this gene were even fatter, but they were protected if they ate a Mediterranean diet.