That's according to new research published in the New England Journal of Medicine.
In people with a high genetic risk for obesity, getting a lot of sugar from sugar-sweetened drinks may amplify the genetic effects on obesity, says researcher Lu Qi, MD, PhD, an assistant professor of nutrition at the Harvard School of Public Health.
Qi's study and two others looked at the effects on weight gain of sugary drinks -- including sodas, fruit punches, lemonades, or other fruit drinks.
The new research should inspire people to give up sugary drinks or consider them an occasional treat, says David Appel, MD. Appel is the director of the Montefiore Medical Center School Health Program and associate professor of clinical pediatrics at Albert Einstein College of Medicine.
"These three studies give very clear evidence that drinking sweetened beverages even in modest amounts clearly results in increased weight and excess weight," he says.
In a statement, the American Beverage Association countered: "We know, and science supports, that obesity is not uniquely caused by any single food or beverage."
Sugary Drinks and Genes
Evidence is already strong, Qi says, that sugary drinks are linked with weight gain.
His team wanted to look at whether the effect of sugary drinks differs depending on individual genetic risk for obesity.
Qi's team looked at more than 33,000 people and calculated a genetic-risk-for-obesity score.
The genetic risk scores ranged from 0 to 64.
For every 10 points on the genetic risk score, those who had the fewest sugary drinks had a 35% higher risk of obesity, he found. This group had less than one sugary drink a month.
For every 10 points on the genetic risk score, those who had the most sugary drinks, one or more a day, had a 235% higher risk of obesity, he found.
"If you reduce your intake of sugary beverages, your genetic risk of obesity may be lessened," he says.
His research found a link between sugary drinks, genetic risk, and excess weight, not cause and effect.
Qi received funding from Amgen for the study.
Sugary Drinks and Weight Gain in Kids
In another study, researchers assigned 641 children, ages 4 to 11 and mostly average weight, to drink either an 8-ounce sugar-free drink or an 8-ounce sugary drink daily for 18 months.
In all, 477 completed the study. The children who drank the sugar-free drink gained less fat, says Martijn B. Katan, PhD, emeritus professor of nutrition at VU University in Amsterdam. They also gained fewer pounds.
Those who drank the sugary drink gained about 16 pounds. Those who drank the sugar-free drink gained about 14 pounds.
While that difference may seem small, it is not insignificant, Katan says.
The size of the drink studied, 8 ounces, is far below the daily average in the U.S., he says. "With average consumption, you could be talking in the United States, say, about [a difference of] 5.5 pounds."
Sugary Drinks and Weight Gain in Teens
In a third study, researchers split 224 overweight or obese teens who regularly drank sugary drinks into two groups.
One group was encouraged to drink fewer sugary drinks during a one-year program. They were followed for another year without a formal program.
The other group was not encouraged to have fewer sugary drinks.
The researchers, from Boston Children's Hospital and Harvard, tracked changes in body mass index (BMI). At two years, there was no substantial difference in BMI between the groups.
At one year, however, the rise in BMI was smaller in the group that was encouraged to have fewer sugary drinks.
Beverage Industry Perspective
Americans are drinking fewer sugary drinks, according to the American Beverage Association. In its statement, it says that calorie intake from sugary drinks declined by more than 20% between 2001 and 2010.
"By every measure, sugar-sweetened beverages play a small and declining role in the American diet," it says.
"Obesity is caused by an imbalance between calories consumed from all foods and beverages and those burned through physical activity," the statement says.
The industry group took exception with the new findings. Among the many criticisms:
- The study in children, it says, did not consider physical activity and total calories.
- The genetic study looked only at the 32 known genes linked with weight, but these account for only a small amount of BMI variation, according to the American Beverage Association.
Advice for Parents
"Parents should do their best at home to have water [for children] instead of soda," Appel says. "We have equated quenching our thirst with a sweetened beverage," he says.
Water can quench thirst, too, he says.
Parents who choose to keep soda at home should give children controlled amounts, Appel says.
"I think all people really don't need to drink sweetened beverages," says Nancy Copperman, RD, director of public health initiatives for North Shore LIJ Health Systems in Great Neck, N.Y. Nutritionally, they are not a beverage of choice, she says.
If quitting sugary beverages cold turkey is difficult, focus on cutting down, she says.
In an editorial, Sonia Caprio, MD, of the Yale School of Medicine, writes: "Taken together, these three studies suggest that calories from sugar-sweetened beverages do matter."
The time has come, she writes, for both children and adults to have fewer sugary drinks.