Has Berkeley's soda tax affected soda consumption?

Soda consumption is down in Berkeley, Calif., but whether that owes more to a soda tax or the public campaign around it is still under debate.

Researchers at the University of California, Berkeley found that soda consumption has plummeted since the tax took effect in January 2015, with residents drinking 21 percent less soda and other sugar-sweetened beverages and 63 percent more water. In neighboring San Francisco and Oakland consumers are drinking 4 percent more soda, along with 19 percent more water. A similar soda tax measure failed to pass in San Francisco in 2014, but both Oakland and San Francisco will be voting on the issue this year.

"We are looking for tools that support people in making healthy choices, and the soda tax appears to be an effective tool," study senior author Kristine Madsen, an associate professor of public health at UC Berkeley, told Berkeley News.

The tax measure added an extra penny per ounce to all beverages sweetened by sugar, including soda, juice, and energy drinks, among others. The measure passed with overwhelming success in Berkeley, although it failed in several other California towns.

Researchers collected their data by interviewing Berkeley residents about their drinking habits both before and after the tax was implemented, polling more than 2,500 people across varying demographics. However, they focused on low-income neighborhoods, which "bear the brunt" of related public health problems, Dr. Madsen said.

Not everyone gives credit to the new tax. Some argue that the decrease in soda consumption was a result of the aggressive campaigning, which led to increased public health awareness.

“It’s possible that successful campaigning around the tax raised awareness of the health impacts of sugary drinks, which may have also shifted dietary choices in Berkeley,” study lead author Jennifer Falbe, a postdoctoral fellow at UC Berkeley, told SFGate. She added that future studies will clear up what contributed to the drop in soda drinking. 

Economists point out that the dramatic decrease suggests that both factors – the price and the health benefits – played a role.

"It makes complete sense that, when prices go up, people buy less. That's the law of demand," John Cawley, a professor of public policy and economics at Cornell University, told NPR. "So I did expect to see some kind of decrease in consumption, but this is a very large decrease."

The American Beverage Association (ABA) disagrees. The organization, which vehemently opposes soda taxes, told SFGate that this study was flawed since it depended on interviews with pedestrians on the street. The ABA defeated the 2014 attempt to institute a soda tax in San Francisco, and has already spent $545,000 on campaigns against the 2016 ballot question.

So far, only Philadelphia has joined Berkeley in passing a soda tax, which will take effect in June 2017. Voters and lawmakers will decide on similar measures this year in San Francisco, Oakland, Illinois, and Colorado.

[Editor's note: The original article gave incorrect information about the vote on a soda tax in Oakland. The vote is coming in November.]