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The risk is especially high for those who grow rapidly during childhood. But having a genetic risk doesn't sentence one to becoming obese, the researchers added.
"Genetic background is far from destiny," said study author Daniel Belsky, a research associate in psychology and neuroscience at Duke University. "Lots of kids with high genetic risk didn't become obese, and some kids with low genetic risk did become obese."
The report was published in the June issue of the journal Archives of Pediatrics & Adolescent Medicine.
For the study, Belsky's group collected data on more than 1,000 people born between April 1972 and March 1973 in Dunedin, New Zealand. These people took part in the Dunedin Multidisciplinary Health and Development Study, which followed them for almost 40 years.
Over that period, the researchers looked at how 32 recently discovered genetic markers for obesity influenced the growth and development of these individuals.
They found children with more of these genetic risk factors were between 1.6 and 2.4 times more likely to be obese as adults, compared with children with a low genetic risk of obesity.
Moreover, children with a high genetic risk started to gain weight sooner after losing their "baby fat" than children at low risk, the researchers noted.
In addition, children at high risk for obesity who grew faster were more likely to be obese, while similar children who grew more slowly were less likely to become obese, Belsky's team found.
"Our research suggests that, even for those who have the genetic predisposition to becoming obese, there are things you can do to mitigate that risk," Belsky said. "For kids who eat healthy and are active early in life, these genetic risks for obesity pose less risk across the life course."
There are rare cases of genetically influenced obesity that are difficult to prevent or treat, Belsky said.
"However, although genetics have an important role to play, they are not destiny," he added. "There are things we can do to reduce the risk we inherit."
Jose Fernandez, associate professor of nutrition at the University of Alabama at Birmingham and author of an accompanying journal editorial, said "obesity is so complex that it will require more than just a genetic test of 32 markers for a person to blame genetics for his or her obesity status, and we cannot forget about the influence of the environment."
The genes evaluated in the study account for less than 2 percent of the variation in body-mass index, so having a genetic predisposition to obesity doesn't mean an individual will be obese, Fernandez said. Body-mass index is a measure of body fat based on height and weight.
"When translating science to public-health implications we must be extremely careful, and nobody should pursue a test of genes associated with obesity and use that information to classify a kid as hopelessly obese," Fernandez said.
Another expert, Dr. David Katz, director of the Prevention Research Center at Yale University School of Medicine, added that "this information can potentially be used to identify individuals at higher risk of developing obesity, and to intervene early in such cases with preventive efforts."
But the big picture is more concerning, Katz said: The U.S. Centers for Disease Control and Prevention recently predicted that obesity rates in the United States could reach 42 percent by 2018.
"We also know that these same genetic mutations were around 100 years ago, when obesity was rare," Katz noted.
Although genes play a role in obesity, modern society has created an environment that all but promotes it, he said.
"If we concentrate our preventive efforts on changing that, we will be providing prevention strategies that reach everyone, no matter their vulnerability," Katz said.
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