(Reuters Health) - As voters consider soda taxes in four U.S. cities, a new study finds that low-income Berkeley neighborhoods slashed sugar-sweetened beverage consumption by more than one-fifth after the Northern California city enacted the nation’s first soda tax.

Cans of soda are displayed in a case at Kwik Stops Liquor in San Diego, California February 13, 2014. REUTERS/Sam Hodgson

Berkeley voters in 2014 levied a penny-per-ounce tax on soda and other sugary drinks to try to curb consumption and stem the rising tide of diabetes and obesity. After the tax took effect in March 2015, residents of two low-income neighborhoods reported drinking 21 percent less of all sugar-sweetened beverages and 26 percent less soda than they had the year before, according to the report in the October American Journal of Public Health.

“From a public health perspective, that is a huge impact. That is an intervention that’s more powerful than anything I’ve ever seen aimed at changing someone’s dietary behavior,” senior author Dr. Kristine Madsen said in a telephone interview.

Madsen, a professor of public health at the University of California at Berkeley, said the drop in sugary drink consumption surpassed her expectations, though it was consistent with consumption declines in low-income neighborhoods in Mexico after it imposed a nationwide tax on sugar-sweetened beverages.

The Berkeley results also pleasantly surprised Marion Nestle, a professor of nutrition, food studies and public health at New York University.

“I hadn’t expected the effects to be so dramatic,” she said in an email. “This is substantial evidence that soda taxes work.”

The soda industry has spent millions of dollars defeating taxes on sugary drinks in dozens of U.S. cities. But the tax passed easily – with 76 percent of the vote – in Berkeley. In addition to soda, the measure covers sweetened fruit-flavored drinks, energy drinks like Red Bull and caffeinated drinks like Frappuccino iced coffee. Diet beverages are exempt.

In June, the Philadelphia City Council enacted its own tax on sugar-sweetened beverages. The 1.5-cent-per-ounce tax is set to take effect in January, although soda trade groups have sued to try to block the measure.

Meanwhile, voters in Boulder, Colorado and the Bay Area cities of San Francisco, Oakland and Albany will vote on whether to tax their sugary beverages on November 8.

San Francisco voters also considered a soda tax in 2014, but it failed to garner a two-thirds majority needed for approval.

Public health officials and politicians point to the Berkeley study as proof of the power of an excise tax to wean residents of low-income neighborhoods off sweetened drinks.

“The study is another tool highlighting how effective a tax on sugary beverages will be on changing the consumption rate,” San Francisco Supervisor Malia Cohen told Reuters Health.

“Just like tobacco, these are commodities we can live without that are killing us,” she said. Cohen wrote the San Francisco ballot measure.

Researchers surveyed 873 adults in low-income commercial neighborhoods in Berkeley and 1,806 adults in similar neighborhoods in nearby San Francisco and Oakland before and a few months after imposition of the soda tax.

Sweetened beverage consumption increased slightly in San Francisco and Oakland at the same time it dropped in Berkeley, the study showed. In Berkeley, water consumption spiked 63 percent, compared to 19 percent in San Francisco and Oakland, after the tax took effect.

The researchers attributed the surge in water consumption to a heat wave. But the American Beverage Association saw it as example of the study’s flaws.

In a statement, Brad Williams, an economist working for the trade group, criticized the research for using “unreliable and imprecise methodology” and producing “implausible” results.

The association’s criticism may hold grains of truth, Nestle said. But she largely dismissed it. “Obviously, the ABA is going to attack the results. That’s rule number one in the playbook: cast doubt on the science,” she said.

Public health experts believe soda helped drive American obesity rates to among the highest in the world. The U.S. spent an estimated $190 billion treating obesity-related conditions in 2012.

Diabetes rates have almost tripled over the past three decades, while sugary beverage consumption doubled.

SOURCE: bit.ly/2ekY7Nu American Journal of Public Health, October 2016.