A first-in-the-nation tax on sugar-sweetened beverages (of just a penny per ounce) was having its intended effect a mere four months after implementation in Berkeley according to a study published in The American Journal of Public Health. As other cities consider taking such measures themselves, the study couldn't have appeared at a more opportune time: Consider, for example, that San Francisco will vote (again) on such a measure this fall. Berkeley's tax, called an excise tax, is incorporated into an item's prices, and researchers concluded that “Widespread adoption of [sugar-sweetened beverage] excise taxes could have considerable fiscal and public health benefits.”

The methods for the study were in-person surveys — so yes, self-reporting, which is inherently problematic — in low-income communities in Berkeley, San Francisco, and Oakland. Surveys were conducted first when the tax passed, in 2014, and then four months after it took effect. According to a New York Times summary of the study, residents reduced their consumption of sugary beverages by 21 percent, while in San Francisco and Oakland, consumption grew four percent.

“While Berkeley is just one small city, this is an important first step in identifying tools that can move the needle on population health,” Madsen said in a statement to the LA Times. The LA Times also notes that according to the 3,000 Berkeley residents surveyed, they were drinking 26 percent less regular soda, 36 percent fewer sports drinks, 29 percent fewer energy drinks, all while consuming 63 percent more water.

Soda industry representatives were quick to criticize the study. "The authors of this street survey acknowledge that it had a number of flaws, and there is no indication that the tax had or will have a measurable impact on public health,” William Dermody, a vice president for policy at the industry trade group American Beverage Association, told the New York Times.

Meanwhile, such groups are gearing up for a fight in San Francisco: The Huffington Post reports that they've reserved about $1 million in TV ad time before the election in the Bay Area. But this year, holding back a soda tax may be harder than before: The tax needs but a simple majority to pass here, rather than the two-thirds majority it failed to achieve last time.

Related: San Francisco Soda Tax Likely Headed Back To Ballot