San Francisco, California - Voters next month could make San Francisco the first place in the United States to adopt a soda tax after similar efforts in dozens of other cities and states have fizzled.

But a soda tax isn’t unprecedented.

Urged on by President Enrique Peña Nieto, Mexico’s legislature adopted a 8 percent tax on sugary drinks last October. The tax went into effect in January, and proponents of San Francisco’s Proposition E on the November 4th ballot point to Mexico’s early results as proof that a similar tax should be adopted here.

Public health researchers surveyed a panel of Mexican consumers living in cities with a population of at least 30,000. Preliminary results show that in the first quarter of 2014, purchases of sugary drinks were down 10 percent compared with the first quarter of 2013.

And purchases of untaxed beverages — such as diet sodas, unsweetened juices, flavored water, milk, and sparkling and still water — increased by 7 percent. Within that category, purchases of plain, unflavored water rose 13 percent compared with purchases of plain water in 2013.

"The Mexico soda tax, from everything we’ve seen, has been a big success," said Supervisor Scott Wiener, a major proponent of Proposition E.

Money for Children’s Health

The measure on the local ballot would levy a 2-cents-per-ounce tax on soda and other sugary drinks. City economist Ted Egan has predicted soda prices would rise by 23 to 36 percent — and that it would lead San Franciscans to reduce their soda consumption by over 30 percent.

The money would go to children’s nutrition and physical education programs, and Egan estimated the funds raised would total $35 million to $54 million annually.

Wiener pointed out that the research showing Mexicans are buying less sugary soda demonstrates two points pushed by backers of Proposition E. First, it shows that consumers are making more healthful choices to avoid paying the tax.

Second, it shows opponents’ claims that the tax would hurt small grocers and kill jobs of union workers who drive delivery trucks, work in bottling plants, and stock shelves are unmerited, he said. People are still buying drinks; they’re just opting for ones containing less sugar.

Roger Salazar, a spokesman for the campaign to defeat the soda tax, said Mexico’s tax and San Francisco’s proposal aren’t a great comparison.

Mexico levies the tax on the purchaser of the drink at the cash register. San Francisco’s tax would be levied on the distributors, meaning grocery stores and other soda vendors would probably raise the total overall cost of groceries to pay it, Salazar said. That means total grocery bills would go up, even if people don’t have Coca-Cola or Pepsi in their shopping carts, he said.

"It will make groceries more expensive across the board," he said.

Major Obesity Problem

The Mexican government was inspired to pass the soda tax after the UN Food and Agricultural Organization named it the industrialized country with the most severe weight problem, surpassing the United States, which previously held the dubious distinction.

In Mexico, about 70 percent of adults are overweight and 32.8 percent are obese. A third of Mexican children are overweight. Fourteen percent of the population has diabetes.

Soda is a huge industry in Mexico, and the average resident drinks half a liter, or roughly 16.5 ounces, of soda a day. A new documentary on the country’s soda tax, "Sweet Agony," shows footage of poor mothers feeding bottles of Coke to their babies instead of milk.

Other Latin American countries are working to restrict the marketing of soda to children and to better label the drinks with their sugar and calorie contents. Some experts predict the Mexican soda tax could be replicated elsewhere in Central and South America.

Like with soda tax proposals in the United States, the soda industry fought hard against the Mexican proposal. The American Beverage Association has poured $7.7 million into the campaign to defeat the soda tax on San Francisco’s November ballot, while soft drink companies created advertisements urging politicians to vote against the tax, warning it would kill jobs in sugar production and close down small shops that sell soda.

Former New York City Mayor Michael Bloomberg financed the drive to adopt the tax in Mexico with a $10 million grant that helped fund billboards showing patients with diabetes who had lost body parts to the disease.

'We Have to Act’

Peña Nieto pledged that the money raised from the soda tax — estimated at 15 billion pesos a year, or about $1.1 billion in US dollars — would go to fund drinking water in schools, many of which have none or have only water that’s unsafe to drink. The designation of the money is winding its way through the Legislature separately.

Rebecca Berner is the institutional development director for El Poder del Consumidor, a nonprofit consumers rights advocacy group in Mexico. She was in San Francisco recently to discuss the soda tax and said the data from Mexico show San Franciscans should adopt one here as well.

"If you raise the cost of soda and sugary drinks a little, we’ll reduce obesity and diabetes," she said. "We have to act."