Exercise associated with reduced effects of obesity gene in teens

"There is compelling evidence that human obesity is a multifactorial disorder where both genes and lifestyle factors, including diet and physical activity, are important contributors," the authors write as background information in the article. "Among the obesity-related genes, polymorphisms in the fat mass- and obesity-associated gene (FTO) are strongly associated with body fat estimates in populations of different ethnic background or ages." Each copy of a mutation in this gene may be associated with a weight increase of approximately 1.5 kilograms or 3.3 pounds.

The U.S. Department of Health and Human Services recently released updated guidelines recommending that children and adolescents participate in physical activity for 60 minutes per day or longer, with most exercise being of moderate to vigorous intensity. To see if this level of physical activity reduces the effects of mutations in the FTO gene on body fat, Jonatan R. Ruiz, Ph.D., of the Karolinska Institutet, Huddinge, Sweden, and colleagues studied 752 adolescents who were part of a cross-sectional study in 10 European countries between October 2006 and December 2007.

Of the participating teens, 275 (37 percent) had no copies of the obesity mutation, 354 (47 percent) had one copy and 123 (16 percent) had two copies. The mutation was associated with a higher body mass index (BMI), higher body fat percentage and a larger waist circumference.

However, among participants who met the daily physical activity recommendations, the effect of the gene mutation was much lower. For each copy of the mutated gene, those who exercised as recommended had a BMI an average of 0.17 higher than those with no mutations, compared with 0.65 higher per mutation among those who did not meet exercise requirements. Similarly, each mutated gene was associated with an increase of 0.4 percent in body fat and a 0.6-centimeter increase in waist circumference among those who met activity guidelines, compared with a 1.7 percent increase in body fat and a 1.15 centimeter increase in waist circumference among those who did not.

"These findings have important public health implications and indicate that meeting the physical activity recommendations may offset the genetic predisposition to obesity associated with the FTO polymorphism in adolescents," the authors write. "Indeed, adolescents meeting the daily physical activity recommendations may overcome the effect of this gene on obesity-related traits."