"Almost everyone carries some genetic risk of obesity," says Frank Hu, professor of nutrition and epidemiology at the Harvard School of Public Health and an author on the study.
"People who carry a lot of obesity genes have a higher risk. People who drink a lot of soda also have a higher risk of obesity. For people who have both, their risk of obesity is much greater than either factor alone," he says.
To come to these conclusions, researchers examined data on 6,934 women from the Nurses' Health Study; 4,423 men from the Health Professionals Follow-up Study; and 21,740 women from the Women's Genome Health Study. Participants in all three studies were of European ancestry; genetic profiles were available on all of them, which allowed scientists to look at the 32 genes associated with obesity.
All participants completed questionnaires on their food and beverage intake over time. Sugar-sweetened beverages included sugary soft drinks, fruit drinks and lemonade. Not included: 100% fruit juice, iced coffee or iced tea.
The participants were divided into categories: those who consumed less than one serving a month of sugar- sweetened beverages; one to four servings a month; between two and six servings a week; one or more servings a day. Researchers made calculations that accounted for participants' overall dietary quality, physical activity, smoking and alcohol consumption. The dietary quality score includes dietary fats, meat intake, fruits, vegetables, nuts and whole grains.
Findings: The risk of becoming obese as a result of carrying a high dose of obesity genes was more than twice as great in the group with the highest intake of sugary beverages as it was for the lowest intake group, says lead author Lu Qi, assistant professor in the nutrition department at the Harvard School of Public Health. This means that regular consumption of sugary beverages magnified the genetic risk of becoming too heavy, he says.
The study is being published online Friday in the New England Journal of Medicine, and Qi is presenting it Friday at the annual meeting of Obesity Society in San Antonio.
"This study indicates that unhealthy diet choices, such as drinking a lot of sugary beverages, can affect how the genes are expressed," Hu says. "Although genetic makeup influences obesity risk, the trigger of the genetic effects may lie in our environment."
Other genetic experts offer a word of caution on interpreting the results. It's hard to know if it's just the sugary beverages that are to blame for the increased genetic susceptibility or if it was influenced by other unhealthy lifestyle factors, says Ruth Loos, director of the Genetics of Obesity and Related Metabolic Traits Program at Mount Sinai School of Medicine in New York. People who drink sugary beverages "tend to be less physically active, have a higher caloric intake and a poorer diet in general," she says. This is illustrated in the new study, she says.
Still, Loos says, there's no reason for people to get discouraged and blame their genes for their weight woes. She has done research that shows that being physical active lowers your risk of obesity, even more so in people with a high genetic susceptibility. Her study and this new one "show that your genetic susceptibility to obesity can be reduced by living a healthy lifestyle," she says.
By Nanci Hellmich, USA TODAY
