San Antonio, TX - A study presented this weekend at Obesity 2012, the annual scientific meeting of the Obesity Society, widened the sugary-beverage/obesity link to include sports drinks. Sales of sports drinks are rising at the same time that sales of sodas are tapering off.

Data on nearly 11 000 offspring of participants in the Nurses' Health Study II, aged nine to 15, were tracked over time by Dr Alison Field (Harvard Medical School, Boston, MA) and colleagues.

By the end of each two-year interval of the study, the teens gained almost two pounds for each can of soda they drank every day. If they drank two sodas a day, they gained four pounds over those two-year intervals. But importantly, this study revealed the previously unknown consequence that teens put on even more weight if they drank a bottle of sports drink each day, averaging 3.5 pounds for every sports drink consumed per day.

"Sports drinks have an even stronger relationship than sugared sodas with weight gain," Field said in an interview. "I was surprised by that. I would have expected the weight gain to be comparable."

Over the life of the study, which began in 2004, consumption of sodas went down slightly among the participants, which mirrors the national trend, but consumption of sports drinks, particularly among boys, increased significantly, also matching the national trend.

"Sports drinks go under the radar," Field explained. "The danger is that they're sold as being part of a healthy lifestyle, of being active. Unfortunately, kids don't get two hours of exercise a day, whereas if that were true, there wouldn't be a problem. Sports drinks also come in very large portions, and there's no line on the bottle that says, 'stop here.' They're simply not aware of how many calories are in a bottle."

Sports drinks are labeled as having 50 calories per serving, but each bottle contains multiple servings, so the calories add up: 130 calories per 20-ounce bottle and 200 calories for 32-ounce bottles. By contrast, sodas are most commonly sold in 12-ounce individual cans or bottles, containing 120 calories.

Kids often drink the entire sports drink container at one time, and they consume all the multiple servings in that single container, Field said. "The label says, 'amount per serving, 50 calories,' but it's not clearly labeled that a quart bottle contains four servings.

"We need to educate parents and clinicians about what constitutes a sugary drink," Field concluded. "Parents don't think of these as sugary drinks, but they should. Sports drinks are promoted by professional athletes as a healthy drink, but they really don't need to be used by kids unless they are continually exercising for long periods or they're in hot climates. I'm a marathon runner, and even I don't consume 32 ounces of a sports drink when I'm running 26 miles."

Dr Daniel Taber (University of Illinois, Chicago) says he sees that schools are substituting sports drinks for sodas, with good intentions, but that it's not making any difference in lowering childhood obesity rates. "This study's results are truly remarkable," Taber said. "Especially the data revealing a bigger effect on a person's obesity from sports drinks than sodas."

Mislabeling is a pervasive problem and is a legitimate subject for improved public policy, according to Field. "One solution would be if beverage companies were required to label the calories per container." It wouldn't matter if it's 12, 20, or 32 ounces, she said, "the container would say how many calories are in it."

The study's limitations included the information being self-reported, and the study group contained few ethnic minorities or youths from low socioeconomic strata.