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By Amanda Gardner

TUESDAY, November 1, 2011 ( — If you are one of the millions of people who are genetically predisposed to , getting more exercise may help you trump the cards nature has dealt you. A new study suggests that even moderate physical activity can reduce the influence of an obesity-related gene variation by more than one-quarter.

This gene variation—sometimes called the "obesity gene"—has been shown to increase the risk of obesity by 20% or more, depending on how many copies of the variation a person inherits. And it's very common: Roughly three-quarters of white people and black people and up to 44% of individuals of Asian descent have at least one copy, according to the study, which was published this week in the journal PLoS Medicine.

Exercise may not be able to neutralize this predisposition entirely, but the study findings drive home the lesson that genes aren't fate when it comes to obesity, says senior author Ruth Loos, PhD, a researcher at the Institute of Metabolic Science, in Cambridge, England.

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    "Even people who are genetically predisposed to [obesity] can, at least in part, reduce that genetic susceptibility by living a physically active lifestyle," Loos says. "Too often, people…may have thought they had no control over their own obesity risk, while we show that they do. It is still hard to lose weight or to stay lean, but it is possible."

    And you don't have to become a marathoner to overcome your genetic susceptibility. Walking the dog, cycling to work, climbing stairs, or engaging in other low-intensity exercise for at least 30 minutes a day five days a week is sufficient to lower your risk of obesity, Loos says.

    "Obviously genetic predisposition is important, but what you do with the disposition is also important," says Mitchell Roslin, MD, the chief of bariatric surgery at Lenox Hill Hospital, in New York City, who was not involved in the study. "We look like our parents, we act like our parents—but we're also in control of our own destiny by how physically fit we are."

    Variations of the fat mass and obesity associated (FTO) gene were first linked to obesity in 2007, and since then dozens of studies have explored the effect of these variations on body size and other health measures. To pin down the role that exercise plays in this relationship, Loos and her colleagues sought out the authors of 54 of these studies and, with their assistance, re-analyzed raw data on more than 218,000 adults and 19,000 children.

    Having a copy of the FTO gene variation increased an adult's odds of being obese by 30%, the researchers found. If the person was physically active, however, the odds of obesity dropped to 22%—a 27% reduction. Similarly, physical activity lowered the odds of being obese from 70% to 49% among adults who inherited two copies of the gene variation.

    Next page: No need to get genetic testing

    Three-quarters of the adults and 13% of the children in the combined studies were considered "inactive." The reduction in obesity risk associated with physical activity was seen only in adults, however, possibly because there were relatively few children included in the study. (As the authors note, assessing the interaction of gene variations and lifestyle factors such as exercise tends to require very large sample sizes.)

    Physical activity is healthy regardless of whether a person is predisposed to obesity, so for now there's no reason to undergo genetic testing to determine if you have the FTO variation, says J. Lennert Veerman, MD, a researcher at the University of Queensland School of Population Health, in Brisbane, Australia.

    The study shows that the "extra weight" associated with gene variations is "not inevitable but can be lost by being active," says Dr. Veerman, who wrote an editorial accompanying the study. "But for persons who don't have those genes, physical activity is also good. If persons are overweight, and even if they are not, it is always advisable to be physically active."