(CNN) - When schools banned all sugar-sweetened beverages such as energy, sports drinks and sugary fruit juices, students bought fewer of these items.
Yet, about 85% of students, regardless of what kind of policy their schools had, drank sugary beverages weekly, according to the study published this week in Archives of Pediatrics and Adolescent Medicine. And 26 to 33% of students reported daily consumption.
"This indicates the school environment is healthier, but that kids are able to compensate in some way, whether they get it at a convenience store, home or fast food restaurants," said lead author, Daniel Taber, postdoctoral research associate at the Institute for Health Research and Policy at the University of Illinois at Chicago.
State laws that restrict sugary drinks in schools have "done what they're designed to do -- they can only go so far. They need to be complemented with other laws," he said.
The Institute of Medicine recommends drinking water, and limited servings of 100% fruit juices and skim or non-fat milk. The institute, an independent, nonprofit organization that gives advice to decision makers and the public, also recommends that all sugar sweetened beverages be banned from schools. This is because soda accounts for more calories than any other food or beverage groups for teens between the ages of 14 to 18.
Overall, 24 states have laws banning soda or sugary drinks from being sold in schools.
"We found many states have laws that ban sodas, but not all other sugar sweetened beverages," said one of the study authors, Jamie Chriqui, senior research scientist at the Health Policy Center in the University of Illinois at Chicago. "What we're finding is that students in middle school tend to still purchase the broader categories beyond soda, perhaps isotonic beverages, sports drinks, energy drinks that's not covered by a soda-only ban. What we found was it requires a comprehensive approach, to reduce sugar-sweetened beverages to be most effective in schools."
The study looked at almost 7,000 students from 40 states. They were sampled in fifth and eighth grades (2004 and 2007) about their beverage consumption habits and whether their schools permitted sodas and other sugary drinks.
"Schools are the target that policy-makers focused on when they started targeting childhood obesity," Taber said. "This was their starting point of improving school environment. We're not going to eliminate obesity overnight. We need to take additional steps ultimately to reduce obesity."
"Schools are huge pieces of the puzzle, but they're not the only pieces of the puzzle," he added.
The study found that when the students' access to sugary drinks became restricted, the infrequent soda drinkers reduced their consumption. But the frequent sugary beverage drinkers increased their consumption "suggesting that heavier consumers compensated to a greater extent with increased consumption outside of school," wrote the authors.
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The American Beverage Association called the paper "effectively useless," because the study looked at data from 2004 and 2007. This was before the industry made changes by only offering juice, low-fat milk and water in elementary and middle schools, according to a statement by the association.
Taber responded by saying that while many changes have taken place to provide healthier beverages, sugary drinks are still available in high schools.
"Despite the incremental progress, there is still a lot of room for improvement as we try to provide students with healthier school beverages," he said.