People who walk briskly an hour a day could beat back a genetic predisposition to be overweight, compared to those who plant themselves in front of the TV, new research suggests.

The findings don’t prove that the exercise is the specific factor that makes a difference, because it’s possible that something else could explain why those who walked were thinner, the researchers stressed. Also, the difference would amount to less than a pound for many people.

Still, “the message is that while we cannot change genes, we can do something to change the influence of genes by increasing physical activity and reducing sedentary behavior,” said study author Qibin Qi, a research fellow with the department of nutrition at the Harvard School of Public Health.

Research has suggested that inherited traits may be responsible for 50 percent of obesity cases, Qi said. As scientists study what makes people fat from a biological point of view, one of the big issues is this: How can you turn back a genetic tide that may make you more likely to put on pounds just because you were born to a specific set of parents?

In the new study, Qi and colleagues tried to tease out an answer. They came up with one, although it has caveats.

The researchers analyzed the results of two studies that tracked about 7,700 female and 4,600 male health professionals. The studies included data about how much time the people spent watching TV and walking in the two years prior to their weight being measured.

The researchers looked at a measurement called body-mass index (BMI) that analyzes whether a person’s height and weight are proportional. The formula is kilograms/meter squared (kg/m-squared).

Genes that have been linked to obesity boosted weight by 0.13 kg/m-squared.

Those who briskly walked an hour a day had a 0.06 kg/m-squared decrease in the genetic effect. For each two hours a day people spent watching TV, the BMI went up by 0.03 kg/m-squared.

The differences wouldn’t amount to much for many individuals. A 6-foot-tall person who weighs 200 pounds would have a BMI of 27.1, and an increase of one pound would boost the BMI to 27.3 — a 0.2 difference.

So should you take an hour-long walk every day to beat back our genetic heritage?

“We don’t know whether it is just physical activity that reduced the genetic risk, or whether a generally healthy lifestyle would have the same effect,” said Ruth Loos, director of Genetics of Obesity and Related Metabolic Traits at the Mount Sinai School of Medicine. “After all, people who are physically active tend to eat more healthily and smoke less, etc., but in these types of studies the contribution of these different aspects of a healthy lifestyle are hard to tease apart.”

The study was scheduled to be presented Wednesday at an American Heart Association meeting in San Diego. Data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.

More information

For more about obesity, try the U.S. National Library of Medicine.

SOURCES: Qibin Qi, Ph.D., research fellow, department of nutrition, Harvard School of Public Health, Boston; Ruth Loos, Ph.D., professor and director, Genetics of Obesity and Related Metabolic Traits, Mount Sinai School of Medicine, New York City; March 14, 2012, presentation, American Heart Association’s Epidemiology and Prevention/Nutrition, Physical Activity and Metabolism 2012 Scientific Sessions, San Diego

Last Updated: March 14, 2012