LOS ANGELES -- As public health leaders step up their efforts to temper Americans' thirst for sugar-sweetened beverages, a new set of published studies has found that removing sugary drinks from kids' diets slows weight gain in heavy teens and reduces the odds that normal-weight children will become obese.
Although sodas, sports drinks, blended coffees and other high-calorie beverages have long been assumed to play a leading role in the nation's obesity crisis, these studies are the first to show that consumption of sugary drinks is a direct cause of weight gain, experts said.
For adults, the new research offers the disturbing suggestion that regular consumption of the high-calorie beverages may turn on genetic switches that incline our bodies to becoming fat.
Collectively, the studies leave little doubt that a steady surge in the consumption of soda and other sugar-sweetened drinks has contributed to the near-tripling of the nation's obesity rate over the last four decades.
"Calories from sugar-sweetened beverages do matter," Yale University endocrinologist Sonia Caprio wrote in an editorial that accompanied the studies, published online Friday by the New England Journal of Medicine. "The time has come to take action."
Admonishing purveyors of crowd-pleasing super-sized drinks, Caprio also urged policymakers to focus first on measures that "limit consumption of sugar-sweetened beverages, especially those served at low cost and in excessive portions, to attempt to reverse the increase in childhood obesity."
More than 12.5 million American kids and 78 million adults are obese. The 40 years of increasing national girth have paralleled an estimated doubling of calories consumed in drinks sweetened with sugar and its close chemical relative, high-fructose corn syrup.
As public health officials have pondered ways to reduce obesity and the chronic diseases that come with it, they have sharpened their focus on the estimated 222 calories the average American drinks every day in the form of sugary drinks and the like.
"Sugar-sweetened beverages -- and ultimately all sugary beverages including juices -- are the low-hanging fruit" of the anti-obesity campaign, said University of North Carolina epidemiologist Barry M. Popkin, an obesity expert who tracks American consumption patterns. While sugary drinks are high in calories, they are low in nutrients, he said. What's more, studies show that people who drink such beverages rarely compensate for their extra calories by reducing intake at meals.
Not surprisingly, the new studies unleashed a storm of objection from the Coca-Cola Co. and PepsiCo Inc., the icons of a $110-billion-a-year industry whose products have penetrated the remotest corners of the earth.
"Sugar-sweetened beverages are not driving obesity," the American Beverage Association, which represents the soda makers, said in a statement released Friday. "By every measure, sugar-sweetened beverages play a small and declining role in the American diet." Citing an analysis of government data by the National Cancer Institute, the ABA said sugar-sweetened drinks accounted for just 7% of the average American's diet. "Focusing on a small source of calories rather than on the total diet is a misplaced allocation of resources," the ABA statement cautioned.
Two of the reports published Friday break new ground in the long-running debate by employing the "gold standard" of biomedical research design: The researchers compared two groups of children who were similar in most respects except that some were randomly selected to drink a sugary beverage each day and some were given an artificially sweetened drink with no calories.
As a result, the findings provide a clear-eyed look at how weight gain is directly influenced by consumption of sugary drinks.
In one of the studies, involving 641 normal-weight children between the ages of 5 and 12, those who drank 8 ounces of a sugar-sweetened beverages each day for 18 months gained more than 2 pounds of additional weight and accumulated more fat than their peers who drank artificially sweetened drinks daily.
In the other study, involving 224 ninth- and 10th-graders who were already overweight or obese, those who were supplied with diet drinks and water for one year were more than 4 pounds lighter on average -- and roughly half a point lower on the body mass index scale -- than their peers who continued to drink sugary beverages. But when those teens were allowed to revert to their old habits, the differences between the two groups disappeared within a year.
"This research pushes us beyond the potential and suggestive effect of sugar-sweetened beverages on obesity and weight gain and into the realm of very solid science," said Popkin, who was not involved in the latest studies.
Latino teens who were overweight or obese showed particularly strong and enduring benefits from switching to calorie-free beverages: After one year, they were an average of 14 pounds lighter than their peers who didn't change their drinking habits, and after two years they were 20 pounds lighter.
"For certain populations, paying attention to these relatively simple things, such as sugar-sweetened beverage intake, can really have an impact," said Dr. David M. Harlan, a leading expert on obesity and diabetes at the University of Massachusetts Medical School.
The third study, which linked regular consumption of sugary drinks with genetic differences in adults, may lend support to a growing belief on the part of obesity researchers that some calories matter more than others. While an individual's weight may be determined by comparing calories consumed and calories expended, some experts believe calories from particular sources -- including super-sweetened drinks -- may have effects beyond the simple units of energy they contain, Harlan said.
The findings, presented Friday at the annual meeting of the Obesity Society in San Antonio, come as momentum builds for a raft of controversial measures that aim to drive down consumption of sugar-sweetened drinks.
Last week, the New York City Board of Health voted to implement a ban on the sale of sugar-sweetened drinks larger than 16 ounces at 24,000 restaurants, snack bars, movie theaters and sports arenas.
In June, the American Medical Association broke a years-long silence and called taxes on sugar-sweetened beverages one effective method of improving health and reducing consumption of the high-calorie drinks. The American Heart Association has already endorsed such taxes, and Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention, has called taxes "the single most effective measure to reverse the obesity epidemic."
The Obama administration and about 30 state legislatures have considered levying sales taxes on sugar-sweetened beverages, prompting beverage manufacturers to spend $60 million on lobbying, according to the Center for Responsive Politics.