Even people with a strong genetic predisposition to obesity can offset their risk of being overweight by being physically active, according to a study published Tuesday in the journal PLoS Medicine.
British researchers examined the effects of 12 genetic variants associated with a higher risk of obesity among 20,430 people in Britain. Researchers calculated a genetic predisposition score for each volunteer that ranged from 0 to 24, representing the number of obesity-related variants they had inherited. (Most of the scores were between 10 and 13.) The volunteers also reported their levels of physical activity.
Armed with that information, the researchers determined that each DNA variant carried a 16% increased risk of obesity among those who were sedentary. But for people who got at least one hour of physical activity per day, the increased risk per variant was only 10% — a reduction of 40%.
In terms of weight gain, each obesity-related gene variant in inactive volunteers was associated with an additional 1.3 pounds in body mass for someone about 5 1/2 feet tall. In people who exercised, the extra body mass was 0.8 pounds, according to the report.
Previous studies have shown that physical activity can offset the effect of genetics, but most have focused on a single gene known as FTO, also known as fat mass and obesity. But many more DNA variants have been linked to obesity in the last three years, said Ruth Loos, program leader at Cambridge University's Medical Research Council Epidemiology Unit and the study's senior author.
"The more variants you carry, the more likely you are to be obese," she said.
Gil Atzmon, a geneticist at the Albert Einstein College of Medicine in the Bronx, N.Y., said the findings underscore that DNA doesn't necessarily mean destiny.
"The message from this is, if you have a genetic predisposition for some things, you can change your lifestyle and contribute to better health," he said.
Loos said she didn't advocate genetic testing for obesity at this point because not enough is known about how these and other variants affect weight.
"Knowing if your parents were obese is a better predictor than knowing your genome, since you not only share genes with your family, but lifestyle as well," she said. But in the future, being aware of one's genetic makeup may help tailor obesity treatments, she added.