Did Philadelphia’s soda tax have an impact on people’s health?

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In 2017, Philadelphia implemented a tax on sweetened beverages, also called the soda tax. The idea was that it would pay for early childhood education. Health advocates also supported it, arguing that sugary drinks are tied to obesity and that a tax would help.

So did it?

Previous studies have already established that the tax led to a drop in sales, based on data from Philadelphia supermarkets and pharmacies, said Christina Roberto, a health policy researcher and associate director of the Center for Health Incentives and Behavioral Economics at the University of Pennsylvania.

She and a group of researchers went deeper to look at electronic health records to compare the body mass index of thousands of patients in Philadelphia, versus people who live outside the city. They found that BMI increased over time in both areas, but the rate at which BMI went up was slower for people in Philadelphia. The new article, which was published this month in the Lancet Regional Health – Americas, concludes that there was “limited evidence” of reduced BMI and obesity prevalence in Philadelphia, due to the tax.

Roberto said that means the tax had some impact in slowing down weight gain, and that it also produced “small but potentially meaningful declines in the actual prevalence of obesity.”

Jessica Jones-Smith, associate professor of health systems and population health at the University of Washington, agrees with the analysis in the Philadelphia study and said it was well-designed. She was not part of that research, and worked on similar research on the impact of a soda tax in Seattle.

Jones-Smith said it’s not clear how much more researchers can study the health impact of these taxes. She suggested that one way to potentially continue the research would be to look at patients who happened to be measuring the levels of glucose or fat in their blood before and after a tax, but those tests are only recommended once every five years for healthy adults, so it would be hard to find a large enough sample.

“What you see here is, in my mind, about the extent of what I think we can legitimately do and potentially attribute to the tax.”

Roberto said that at first, she was skeptical that one policy would have any health impact, because many factors play a role in obesity, like the environment, and access to healthy food.

“That’s a really tall order for any one policy to actually translate into health gains, particularly because the human body is designed in such a way that when we gain weight, it is incredibly hard to lose.”

She concluded that soda taxes do have an effect on people’s health, when taking into account the research on similar policies elsewhere, like Seattle, Mexico and the U.K.

“None of these studies are showing massive reductions in obesity, but when we’re thinking about 1 to 3 percentage point changes in some cases, declines in obesity prevalence, that’s a huge deal, especially from a policy that’s targeting just one unhealthy food group,” Roberto said. “I studied dietary change for 25 years. I’ve done behavioral weight loss treatment with patients. It’s incredibly hard to change dietary behaviors. And this tax does a profound job of doing that while raising money for the city. So I just think it’s such a no-brainer policy.”