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What matters more for obesity risk, genes or lifestyle?

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A new study suggests that genetics is not destiny when it comes to your odds of becoming obese.

For years, research into "obesity genes" has led many Americans to believe that their DNA makes becoming overweight and obese inevitable.

Genetic 'risk score'

But the new study shows that daily lifestyle – not genes – probably plays the much bigger role.

The study tracked data on more than 2 500 Americans who were followed for decades – from young adulthood in 1985 to 2010.

Researchers used modern technology to construct a genetic "risk score" for obesity for each participant, based on their individual DNA. They also tracked changes in each person's body mass index (BMI) over time, to gauge their levels of weight and fitness.

The bottom line, according to lead researcher Dr VenkateshMurthy, is that "we found fitness is a better predictor than genetics of where your BMI will go over time".

"Genetics clearly has some influence, but other factors are stronger," said Murthy, who is an associate professor of internal medicine and radiology at the University of Michigan, in Ann Arbor.

So, your BMI – a measure of weight divided by height – in youth appears to be the best predictor of your long-term obesity risk.

Eating well and exercising

That made sense to one expert in weight management.

"BMI, even at young age, represents both genetics and environment," noted Dr Mitchell Roslin, chief of obesity surgery at Lenox Hill Hospital in New York City.

"Many believe that genetic means destiny," he said, but "no, what is inherited is a susceptibility that is influenced by your behaviour."

The new research supports the notion that "no matter your genetic code, the best method to optimise health is eating well and exercising daily", said Roslin.

Murthy's team found that, when considered in combination with a person's age, sex and history of an overweight parent, BMI in young adulthood explained 52.3% of a person's BMI 25 years later.

In fact, they believe this combo of environmental factors could explain up to 80% of a person's BMI variation over time.

DNA mostly not the 'key'

In contrast, adding genetics into the mix explained only about 13.6% of BMI 25 years later, Murthy's group said.

"There's been a lot of attention to the idea of using genetic information to understand your risk of obesity or being overweight, and for potential drug development to address those genetic risks," Murthy said in a University of Michigan news release.

"We wanted to understand how, if at all, genetic data would add to the information already routinely available in clinic. It turns out, our standard clinical exam, including an assessment of BMI, actually has vastly more information to help guide patient care," said Murthy, who is also a cardiologist at Michigan Medicine Frankel Cardiovascular Center.

The study was published in the journal JAMA Cardiology.

A person's DNA is not the key to obesity for most Americans, agreed study senior author Dr Ravi Shah.

"Genetic risk may be most important [only] in those individuals with rare inherited causes of obesity," said Shah, who is an assistant professor of medicine at Harvard Medical School.

BMI much easier

Instead, "for the majority of the population at risk for becoming obese, universal recommendations like healthy eating and remaining active are important and should be reviewed regularly with your personal physician," he said.

Murthy noted that calculating BMI is also much easier and cheaper than genetic testing, so doctors could have weight/height records for patients on hand for discussions about their risks for obesity.

Dr Benjamin Hirsh directs preventive cardiology at Northwell Health's Sandra Atlas Bass Heart Hospital in Manhasset, New York. Reading over the new findings, he agreed that "health habits have a much greater influence on future body weight than genetics".

But changing bad health habits – unhealthy eating and sedentary lifestyles – is easier said than done, Hirsh noted.

"Obesity is complex and, unfortunately, will continue to rise at ever increasing levels until we have more robust methods to effect change in the American lifestyle," he said. "These methods will require societal change through the influence of policy makers, health organisations and respective governing bodies."

Image credit: iStock

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