Taxing diet soda, as some Philadelphia City Council members are suggesting,  may well have a sweet pay-off for things like education, libraries and children's programs.

But is the disincentive to buy those diet drinks likely to be a boost for health?

The answer depends on what study you read. For sure, sugar-containing sodas have few if any friends in  health- and diet-conscious circles. All those calories, all that sugar.

But in recent years, diet soda has also been called into doubt, particularly with regard to obesity and diabetes. Some studies have suggested that people who drink diet sodas make up the calories saved by eating other things, others have found that using artificial sweeteners are linked with a higher risk of type 2 diabetes.

Still another study found using artificial sweeteners did not cause weight gain.

Thomas Wadden, director of the Center for Weight and Eating Disorders of the University of Pennsylvania's Perelman School of Medicine, said he does not believe there's strong evidence showing  that diet soda is actually harmful.

For those who have been consuming sugar-containing drinks (who don't make up the calories in food), a switch to diet soda is likely to result in a small weight loss, Wadden said.

As for a link between diet soda and Type 2 diabetes, Wadden said the findings have not been definitive.

"I think the evidence is pretty mixed," he said.

Bottom line: He's not promoting diet soda consumption,  but he isn't seeing enough to sound alarms about it.

"From my standpoint, diet soda looks okay," both in terms of diet and health, Wadden said.

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