A study by Swedish researchers has revealed that with regular exercise, teenagers genetically predisposed towards obesity can lose weight and keep it off. The study was carried out in ten European countries over 14 months and involved 753 teenagers. The A allele of a gene called FTO (fat mass and obesity associated gene) is known to be linked with high body mass index (BMI), such that possession of one FTO A allele is equivalent to an average 3.3 pounds of extra weight. Sixteen percent of the group studied possessed two FTO A alleles, 47% possessed one A allele and 37% did not possess any A alleles. Of all the teenagers who exercised for at least one hour daily, it was found that BMI was similar (only 0.17 higher) when comparing those with FTO A alleles and those without. However, comparing teenagers who did no exercise, the difference was significant – BMI was 0.65 higher in those with FTO A alleles. (Attenuation of the effect of the FTO rs9939609 polymorphism on total and central body fat by physical activity in adolescents: the HELENA study. Arch Pediatr Adolesc Med. 2010 Apr;164(4):328-33).