Amid fervid criticism that New York City risks becoming a nanny state, city health officials this month banned the sale of supersize sugar-laden drinks in restaurants and movie theaters. Now scientists have handed the ban’s advocates a potent weapon: strong evidence that replacing sugary drinks with sugar-free substitutes or water can indeed slow weight gain in children.
Two-thirds of all adults and one-third of children in the United States are overweight or obese. Two new randomized clinical trials published Friday in The New England Journal of Medicine lend credence to the idea that limiting access to sugary sodas and fruit drinks may help reduce obesity.
Beverage industry officials denounced the research, which may fuel wider efforts to curb consumption through taxes or other restrictions.
In one of the new trials, researchers at Boston Children’s Hospital randomly assigned 224 overweight or obese teenagers to receive home deliveries of bottled water and diet drinks for one year. The children also were regularly encouraged to avoid sugary drinks. Those who received the shipments gained only 3.5 pounds on average during that year, while a comparison group of similar teenagers gained 7.7 pounds. The differences between the groups evaporated after the deliveries stopped.
In the second trial, researchers at VU University Amsterdam randomly assigned 641 normal-weight schoolchildren ages 4 to 11 to drink eight ounces of a 104-calorie sugar-sweetened or noncaloric sugar-free fruit-flavored drink every day from identically branded cans. Over 18 months, children in the sugar-free group gained 13.9 pounds on average, while those drinking the sugar-added version gained 16.2 pounds.
“So many things are driving obesity that changing any one thing is not going to reverse the problem, but these studies suggest soda is a pretty darn good place to start," said Kelly Brownell, director of the Rudd Center for Food Policy and Obesity at Yale.
He is an author of an editorial accompanying the studies that argues that the government should more aggressively regulate food industry practices.
“Just think what the impact would be if you could create a public policy that would have the same effect as their intervention, but on millions of people," he said.
Officials with the American Beverage Association, the trade association for makers of nonalcoholic beverages, criticized the studies, saying that obesity is not caused by a single food or beverage and that sugar-sweetened beverages make up an estimated 7 percent of the calories in a typical American diet.
Industry representatives also pointed out that the intervention in the two-year Boston study did not produce lasting changes in habits or body composition once it ended.
But Dr. David Ludwig, the director of the New Balance Foundation Obesity Prevention Center at Boston Children’s and the study’s senior author, said the finding only underscored the need for public policy changes.
“It suggests that if we want long-term changes in body weight, we will need to make long-term, permanent changes in the environment for children," he said.
The effectiveness of such changes may vary by ethnic group, Ludwig and his colleagues found. Hispanic children responded more strongly than non-Hispanics to the switch to sugar-free beverages, gaining less than a pound on average by the end of the second year in the Boston trial, while Hispanics in the comparison group gained more than 20 pounds on average.
Ludwig said that this analysis must be interpreted with caution because the Hispanic subgroup was very small, but that it may suggest a greater sensitivity to carbohydrates in the diet among Hispanics in the United States, who have high rates of diabetes.
The Dutch study was double-blinded, meaning neither the researchers nor the children knew whether they were given sugar-sweetened or sugar-free drinks. Dr. Martijn Katan, emeritus professor of nutrition at VU University Amsterdam, developed fruit-flavored drinks that contained either sugar or noncaloric artificial sweeteners in identical cans.
A weakness of this study was that one-quarter of the children dropped out before its conclusion. But the children who were assigned to drink the sugar-free beverages not only gained less weight over the course of the 18-month study but also had less body fat and thinner skin folds.
“When you change the intake of liquid calories, you don’t get the effect that you get when you skip breakfast and then compensate with a larger lunch," Katan said. “You skip the sugary drink and never notice it, which means that this is a less painful way of losing weight."
Still, Katan and others warned that studies need to examine how consumers react to policies restricting access to sweetened drinks, because such policies could have unintended consequences. Taxing soft drinks could result in consumers buying fewer fruits and vegetables so they can afford soft drinks, he suggested.
Both clinical trials had limitations, but they are unusual in that they demonstrate the effect of a single behavioral change on weight gain, said Dr. Seema Kumar, a pediatric endocrinologist at the Mayo Clinic Children’s Center.
“Typically when you do a weight loss intervention, we talk about multiple aspects, changing food choices, portion sizes, frequency of snacks, types of snacks," she said.
Still, she added, curbing soda consumption “is not a magic pill."