Gym vs. Genes: How Exercise Trumps Obesity Genes

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Our genes may have a lot to do with the way we look and behave, but they certainly don’t dictate our destiny. That’s true when it comes to our weight too.

Scientists at the Institute of Metabolic Science in the U.K. report in the journal PLoS Medicine that people who are genetically predisposed to obesity can counter the influence of their DNA by doing even moderate amounts of exercise. People in the study weren’t marathoners or gym rats; rather, they got about 30 minutes of exercise five days a week by walking the dog, riding their bike to work or tending their gardens.

“This should convince people who think that their weight is in their genes, and sit back and say they can’t do anything about it, that they can so something about it,” says Ruth Loos, program leader in the MRC Epidemiology Unit at the Institute, who led the study. “It’s not easy, but you can.”

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The study focused on people with inherited variations of the FTO (for fat mass and obesity associated) gene, which was first linked to obesity in 2007. The current research involved a re-analysis of data from dozens of previous studies, which included more than 218,000 participants with at least one copy of an FTO variation. The researchers found that having a copy of an FTO variation increased an adult’s risk of obesity by about 30%. But if that person exercised, it cut the risk to 22% — a 27% drop in risk. In people with two copies of the genetic change, physical activity was found to reduce obesity risk by 30%, from 70% to 49%.

How common are these gene variations? About 74% of people from Europe, 76% of African Americans and 44% of those of Asian descent carry a copy of an FTO variation.

Loos launched the current study after finding similar results in her previous research. In that analysis, she looked at 12 different genes related to obesity, and scored participants on how many genes they had, as well as whether they had inherited one or two copies of each gene from their parents. On average, of 24 possible copies they could get, most adults were born with about 10 or 13. The more copies they had, not surprisingly, the more obese they were. But even among people with a larger tally of obesity genes, Loos found, those who exercised lowered their obesity risk by 40% compared to those who were sedentary.

Other groups have also found that physical activity can trump genes. One study published in 2008 in the Archives of Internal Medicine looked at an Amish population with copies of FTO variations, finding that the hard-laboring members of that community could overcome their genetic predisposition to weight gain by doing their daily chores.

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But some investigators couldn’t replicate these results, so Loos wanted to confirm the relationship once and for all. She contacted all the researchers who had previously studied FTO and asked for both their published and unpublished data in order to conduct a comprehensive analysis of how exercise may affect the influence of the gene. Using raw data was important, Loos says, because published data can be biased toward positive findings; many scientists choose not to report on data that fails to show a relationship between the gene variations and physical activity.

Loos and her colleagues also standardized the data, so that they could measure physical activity consistently — they defined it as more than one hour of moderate to vigorous leisure or commuting activity each week.

Exactly how exercise overcomes the effects of genes like FTO isn’t obvious yet, but early evidence suggests that physical activity can trigger changes in gene expression, making some health-promoting genes more active while suppressing others like those linked to obesity.

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But whether or not you’ve inherited fattening variations of FTO — and regardless of weight — engaging in regular physical activity is obviously still a good idea. It improves your physical and mental health in many measurable ways. It doesn’t take much, says Loos, but you do have to get moving.

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Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.