-- Doctors have long known that genetics can predispose some people to gain weight despite a healthy lifestyle while others seemingly never gain an ounce no matter how much they eat. A new study sheds light on how people can counteract their genetic makeup, even if it's in their DNA to put on more weight than others.
Researchers from University of North Carolina Chapel Hill, the University of Copenhagen and other institutions conducted a meta-analysis examining 60 past genetic studies to see if physical activity could mitigate the effects a genetic predisposition to weight gain.
"Decline in daily physical activity is thought to be a key contributor to the global obesity epidemic," the authors wrote. However, they explained that genetic make-up may also play a role in weight gain for people who are not physically active.
They screened for 2.5 million genetic variants in 200,452 adults and also separated the subjects between those who were physically active -- about 77 percent -- and those who were physically inactive, about 23 percent. The researchers then looked at different markers that would indicate if a person was overweight including their body-mass index, waist circumference and hip-to-waist ratio.
They found those with a genetic variation that predisposed them to gain weight -- called an FTO gene -- had the ability counteract the effects that gene through exercise. By looking at the data they found that those with the FTO gene who were physically active were able to reduce the weight-gain effects associated with the gene by about 30 percent.
Dr. Goutham Rao, chairman of Family Medicine and Community Health at University Hospitals Cleveland Medical Center, said this type of research is key in helping patients better understand their weight and health.
"Despite that sort of bad luck of having a genetic predisposition to obesity if you are physically active ... you're not going to reduce risk of obesity entirely but you reduce it significantly," Rao said.
The mechanism that leads to people with FTO to be predisposed to gain weight is still not fully understood, but Rao said it's key to give people encouragement that taking healthy steps has an effect even if they haven't reached their goal weight.
"The message is to be sympathetic," Rao said. Explaining he tells frustrated patients, "if you weren't doing your best you would weigh a lot more and be much less healthy."
Dr. Kevin Niswender, associate professor of medicine, molecular physiology and biophysics at Vanderbilt University Medical Center, said the study took on the "really interesting question" of if people can counteract their genetics through their lifestyle.
"This study definitively confirms that lifestyle has an impact," he said.
During their research the team also discovered 11 new genetic variants that likely predispose a person to weight gain and they said more may be found through similar studies.
"In future studies, accounting for physical activity and other important lifestyle factors could boost the search for new obesity genes," said Mariaelisa Graff of the University of North Carolina at Chapel Hill, the lead author of the study. "To identify more genes whose effects are either dampened or amplified by physical activity, we need to carry out larger studies with more accurate measurement of physical levels."
Niswender said finding new variants that indicate predisposition for weight gain can help give a better understanding of the complex mechanisms behind obesity.
"For a long time we've been searching for this gene, the gene that causes obesity and it's just not like that," Niswender."there are a bunch of genes that cause obesity and the effect of each gene variant is really quite small."
Graff said more study should need to be done to get more accurate measurements of the participants' physical activity. The researchers classified those as having a sedentary job, commute and leisure time as "inactive" while everyone else was declared physically active. Additionally, the study was done primarily in people of European descent, so the findings may not be be easily extrapolated to other groups.