People Who Are Genetically Prone to Obesity Need to Work Out Harder to Avoid Weight Gain

Some people are genetically predisposed to obesity — and must work out harder than those without the same genes to achieve the same results, according to a new study.

Using data from the National Institutes of Health's All of Us Research Program, researchers from Vanderbilt University Medical Center (VUMC) looked at people with a genetic risk of reaching a higher Body Mass Index (BMI) and were able to determine how much physical activity they needed to avoid being obese. They published their findings Wednesday in JAMA Network Open.

BMI is "a person's weight in kilograms divided by the square of height in meters," the CDC explains. If a person's BMI is "30.0 or higher, it falls within the obesity range." 

The classification of someone as "obese" can be murky, as BMI is a historically flawed health standard, especially for people of color. But it's currently the primary benchmark used by health professionals.

As the study's authors point out, each person's history needs to be considered when figuring out their risks of obesity.

The biggest issue, they said, is what's lurking in their DNA.

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"Physical activity guidelines do not account for individual differences," senior author Douglas Ruderfer, PhD, associate professor of Medicine, Division of Genetic Medicine, and director of the Center for Digital Genomic Medicine at VUMC said in a statement. 

"Genetic background contributes to the amount of physical activity needed to mitigate obesity. The higher the genetic risk, the more steps needed per day."

The study looked at 3,124 middle-aged participants without obesity, who walked an average of 8,326 steps per day, as tracked by a Fitbit device. 

They then compared the participant's Polygenic Risk Score — which the CDC explains can "provide a measure of your disease risk due to your genes" — for obesity. 

"Although often attributed to unhealthy lifestyle choices or environmental factors, obesity is known to be heritable and highly polygenic - the majority of inherited susceptibility is related to the cumulative impact of many common DNA variants," the National Institute of Health explains.  

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The study found that those genetically at-risk of obesity (whose Polygenic Risk Score was in the 75th percentile) needed to walk 2,280 more steps per day (a total of 11,020 steps per day) than those in the 50th percentile.

And those in the 75th percentile who also had a BMI of 22, 24, 26 and 28 would need to walk an additional 3,460, 4,430, 5,380 and 6,350 steps per day, as compared to those in the 25th percentile — even though those with a BMI of 22 and 24 are classified in the "healthy" range, per the CDC.

"What is new and important from this study is that we were able to put a number on the amount of activity needed to reduce the risk," lead author Evan Brittain, MD, associate professor of Medicine in the Division of Cardiovascular Medicine at VUMC and lead investigator in Digital Health for the All of Us Research Program Data and Research Center, said a statement.

"We would like to test whether knowledge of one's genetic risk for obesity actually has an impact on their behavior," Brittain said. 

"I think these findings could be empowering for patients because the current physical activity guidelines take a one-size-fits-all approach, and what we learned is that depending on your genetic risk, the guidelines may underestimate the amount of activity needed to reduce your risk of obesity."