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". Sugary drinks - including fruit-flavored drinks, sports drinks, sweet teas, sodas and energy drinks - have little nutritional value and are a culprit in high rates of heart disease, diabetes and tooth decay. "(The tax) is one tool that could level the playing field in terms of health".

One of the biggest questions surrounding the issue was whether or not these kinds of taxes actually reduce Americans' consumption of sugary sodas. At the same time, consumption of soda and other sugary drinks increased 4 percent in the low-income neighborhoods of Oakland and San Francisco, Calif., where the tax was not implemented. For sodas in particular, 69% of the tax was incorporated into the price. She added that the beverages offered essentially no nutritional value to compensate for the adverse health effects.

Joe Arellano, a spokesman for the No Oakland Grocery Tax Campaign, claimed the study was "fundamentally flawed" because researchers incentivized study participants to take the survey using free water bottles and did not take into account whether each participant lived in Berkeley.

"Right after a campaign where the community clearly has gotten behind sticking it to Big Soda and the tax, it may well have impacts on responses", Williams told SFGate.com.

Berkeley residents say they increased their water consumption by 63 percent, while the neighboring cities' low-income residents drank only 19 percent more water during the study period. They drank 26% less soda after the tax went into effect, while their neighbors drank 10% more.

She added that while Berkeley and Philadelphia are very different cities, "we know that taxes like this, regardless of location, do not improve public health". Most taxes haven't been around long enough to get a clear sense of how they impact purchases and, importantly, health in the long term.

The findings were based on interviews with Berkeley residents in 2014 and again between April and August 2015.

If soda companies want to convince people to continue to drink soda, they need to cut sugar and calories. An attempt that year in San Francisco failed to gain the two-thirds majority needed to become law.

The new study was published this week in the American Journal of Public Health. In that country, sugary drink sales fell by about 17 percent among the poorest households by the end of a year. The industry spent more than $9 million on its successful 2014 effort to defeat San Francisco's soda tax.

In a sign that taxes can work in the fight against obesity, a new study from the UC Berkeley shows a 21% drop in the drinking of soda and other sugary beverages in Berkeley's low-income neighborhoods after the city levied a penny-per-ounce tax on sugar-sweetened beverages.