Three new studies, conducted by researchers in Boston and elsewhere, show how much sugar-sweetened beverages can expand our waistlines and provide strong evidence in favor of government policies to curb consumption of soft drinks and fruit juices in schools.
The research, published online Friday by the New England Journal of Medicine, found that switching from high-calorie sweetened beverages to noncaloric drinks led to less weight gain among both obese and normal-weight children.
And, in adults who are genetically predisposed to obesity, avoiding sugary drinks appears to virtually negate the effects of obesity genes, according to a Harvard School of Public Health study.
“These studies together provide a high level of confidence for the adverse health effects of sugary beverages on a population basis,” said Dr. David Ludwig, head of the New Balance Foundation Obesity Prevention Center at Boston Children’s Hospital, who coauthored the clinical trial on obese children.
That study, involving 224 overweight teens, randomly assigned one group to switch to calorie-free drinks and the others to remain on their normal diet. After a year, those in the calorie-free group weighed an average of four pounds less than those who drank sugary beverages.
For adults who carry several of the known gene mutations that increase the risk of obesity, sweetened drinks may increase their risk even more.
Harvard researchers analyzed sugary drink consumption in thousands of volunteers who had a genetic predisposition to obesity and found that those who avoided high-calorie beverages had only about a 20 percent greater likelihood of becoming obese over the decades, compared with those who did not have this predisposition. Those who drank sugary sodas daily had five times the likelihood.
“I think we can draw two conclusions from this,” said study coauthor Dr. Lu Qi, assistant professor of nutrition at the School of Public Health. “Having a higher genetic risk for obesity may exaggerate the adverse effects of sugar-sweetened beverages,” by perhaps causing the body to more readily store the calories as fat.
Alternatively, he added, those sugary drinks may exaggerate the genetic effects of obesity by boosting a person’s appetite for sweets.
The study, though, did not measure whether cutting back on high-calorie sodas could reverse obesity in adults who already are overweight, which has been a tough challenge for those looking to shed pounds permanently.
That’s why public health officials have largely turned their efforts toward preventing weight problems in children by targeting calorie-dense junk foods such as soda, chips, and fat-filled sweets.
Massachusetts public schools implemented new rules this year banning all soft drinks, sugar-sweetened beverages — except flavored milk, which will be eliminated in 2013 — and limiting fruit juice servings to no more than 4 ounces. They also banished chips, cookies, and cakes from lunchrooms and vending machines. The new standards also require that schools provide free water.
But lack of easy access to water has caused a few snags in the Boston public schools, which were among the first to adopt the soft-drink ban in 2004 and the free-water mandate last year. Schools without functioning water fountains or safe tap water have to contend with 5-gallon water dispensers in hallways that must be regularly switched out and stored.
Michael Peck, food and nutrition services director in the Boston system, said he has been in schools where empty jugs are stacked to the ceiling and where dispensers sit empty in cafeterias because school staff has not had a chance to replace them with filled ones.
It is hard to predict the effect of policies aimed at reducing the state’s childhood pediatric obesity rate — about 34 percent of school-age children are overweight or obese — which appears to be stabilizing.
Even in the Children’s Hospital study, one year after overweight teens stopped receiving free noncaloric beverages, all their weight-loss benefits had been erased, with the exception of the Hispanic participants who had maintained their healthier body mass index.
In a Dutch study also published Friday in the New England Journal, normal-weight children who were provided with sugar-free drinks over 18 months had significantly less weight and fat gain compared with those who continued drinking sugary soda and juice. Unfortunately, 26 percent of the children dropped out of the study before it was completed.
The American Beverage Association objected to singling out sugary drinks as the culprit of the obesity epidemic. In response to the new research, the group said, “Studies and opinion pieces that focus solely on sugar-sweetened beverages, or any other single source of calories, do nothing meaningful to help address this serious issue.”
But University of Alabama obesity researcher David Allison, who has been a vocal critic of government policies that limit access to sugary beverages, applauded the findings. “These are the important kinds of studies I have been calling for, so that we may make our judgments on a sound scientific basis,’’ he said. “The task for future research is to see if these beneficial effects can be increased in magnitude and duration.”
Allison has received grants and financial compensation from beverage manufacturers.