FRIDAY, Sept. 12 (HealthDay News) -- Banning soft drinks in elementary schools may not make a huge difference in kids' overall consumption of the beverages, a new study suggests.

A researcher found that fifth-graders whose elementary schools didn't allow the sale of soft drinks consumed just 4 percent less overall than those children in other schools.

"It's a pessimistic picture I'm painting here," said study author Meenakshi M. Fernandes, a doctoral fellow at the RAND Corporation in Santa Monica, Calif.

The availability of soft drinks on grade-school campuses has been a hot topic in recent years, with California becoming the first state to ban their sale at elementary schools -- in 2003. Critics of the sale of soft drinks say they contribute to obesity among young people.

"Some foods provide calories along with valuable nutrients and are an important part of the diet," said Dr. David Katz, director of the Yale University School of Medicine Prevention Research Center. "Then there are foods that provide calories and essentially nothing of value. Soda tops the list."

It's difficult, however, to figure out just how responsible soft drinks are for childhood obesity, Katz said. "Trying to define 'the' cause of childhood obesity is like trying to decide which snowflake in a lethal avalanche is guilty," he said. "No single snowflake kills, but they can't all be innocent either, because all together, they do lethal damage. The obesity epidemic is like that, too."

In the new study, published in the September issue of the Journal of the American Dietetic Association, Fernandes analyzed a survey of 10,215 fifth-grade students in 2,303 schools across 40 states.

Almost 40 percent of the schools offered soft drinks for sale, mostly through vending machines. Private schools were more likely than public schools to offer the drinks.

One-quarter of students who attended schools that sold soft drinks reported buying at least one a week. African-Americans and poor students were most likely to buy soft drinks. The survey didn't distinguish between students who drank diet soft drinks and those who drank the sugary kind.

Fernandes said she was surprised that students who attended schools without soft drink sales consumed just 4 percent fewer soft drinks than other students. The 4 percent difference was "statistically significant, but I would have expected the magnitude to be greater."

So, what's the next step in trying to fight the epidemic of childhood obesity? Fernandes suggested that limiting availability of soft drinks at schools "doesn't seem to be the answer."

"We need to take a more comprehensive look at environments around schools, what (students) are doing at home and after school," she said. "Perhaps we can have a greater impact through interventions this way."

Katz agreed. "If there were no soda in school, less soda would be consumed," he said. "But to reduce intake much more, families need to get into the act, too."

More information

Learn more about the link between soft drinks and obesity from the Center for Science in the Public Interest .