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If soda taxes are going to make a dent in childhood obesity, they've got to be pretty steep

April 1, 2010 |  5:00 am

For those bleeding hearts holding out hope that some legislature will take on the obesity crisis by raising soda taxes, researchers are offering this advice: Those taxes had better be pretty steep.

A group of researchers from Rand Corp. and the University of Illinois at Chicago gathered data on more than 7,000 elementary school children, including their body mass indexes, their soda-drinking habits and the amount of time they spent engaged in "vigorous activity" and watching TV. The researchers matched that up with the tax rates on soda and other sugar-sweetened beverages in the states where they lived.

None of the states taxed soda at a rate above 7%; the mean was 4.2%. On average, the tax rate on soda was 3.5 percentage points higher than the rate for other foods. 

Most important, none of these taxes had any significant effect on the amount of soda consumed by the kids as a whole or on the amount of weight they gained. The researchers calculated that a 1 percentage point tax increase was associated with a BMI reduction of only 0.013 points, on average.

Based on those figures, they reported that taxes on soda would have to be at least 18 percentage points higher than for other foods to reduce kids' BMIs by 0.23 points -- enough to trim their weight gain by 20%. But they were quick to recognize that such a huge tax is politically implausible.

They did find that taxes in place today were enough to reduce weight gain in children who were already deemed overweight. They also found that existing taxes on soda were associated with reduced soda purchases at school among three groups of children: those from low-income families, those who were African American and those who watched a lot of TV.

The study will be published in the May issue of Health Affairs.

Even before it was officially released Wednesday night, pundits were getting out their soapboxes to remind us all that no single food or beverage can be blamed for the weight gain observed in this country. The researchers acknowledged this too. But they added that "the intake of sugar-sweetened beverages by itself is much higher than the energy imbalance that underlies the obesity epidemic among youth." They also mentioned that kids now drink 200 calories worth of sugary beverages each day.

-- Karen Kaplan