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A groundbreaking tax on sugar-sweetened beverages recently passed in Mexico could provide the evidence needed to justify similar laws across low- and middle-income countries and cities in the US, experts believe.

Campaigners and public health experts are watching closely to see what impact Mexico's tax has on consumption. Mexico, where 32.8% of the population is obese, is now the country with the biggest weight problem in the world, according to the UN's Food and Agricultural Organisation, overtaking the United States. The impact on health has been serious – 14% of the population has diabetes. Rates of high blood pressure, which can lead to stroke and heart attacks, are also high.

So far, there is not conclusive evidence from any country in the world that raising the price of sugar-sweetened drinks will affect obesity levels, but the Mexico experiment is on an unprecedented scale. Although the tax was set at 10% per litre rather than the 20% campaigners wanted, it will affect a huge number of people. Every year, Mexico's 118 million people drink 163 litres of soda each, or nearly half a litre a day. According to the National Institute of Public Health, a 10% tax should reduce that to 141 litres per year, preventing up to 630,000 cases of diabetes by 2030.

Other countries in Latin America, including Ecuador, Peru and Chile, are working on their own measures to reduce the marketing of soft drinks to children, and to improve labelling so families can know how much sugar and calories they contain. “Mexico will have a domino effect,” said Dr Simon Barquera of the Institute. Public health academics, students, consumer activists and politicians were all following developments and sharing what they are doing in their own countries on Twitter, he said.

“One of the vice-presidents of the big companies told me they had done their studies and the soda tax will not reduce consumption or solve obesity,” he said. “We know that. My kids know that. But it is an educative tax. It sends a message from the government to the people that we think this is bad for you.”

Tom Farley, health commissioner of New York City, where a proposed ban on large sugary drinks was struck down by the courts, is also watching developments in Mexico. “I am hopeful that with the passage of that in Mexico, when people see the benefits, legislatures around the country [the US] will be supportive of it,” he said.

The tax was passed in October, to the surprise even of many of its supporters, after an unprecedented, hard-hitting advertising campaign from civil society organisations funded by Bloomberg Philanthropies, which has extended its public health work on tobacco prevention into the areas of road safety and obesity.

President Enrique Pena Nieto gives his first state-of-the-nation speech in Mexico CityPresident Enrique Peña Nieto in Mexico City. Photograph: Dario Lopez-Mills/AP

Billboards across Mexico City ran photographs of a man with parts of his feet missing as a consequence of diabetes. They warned that a 600ml litre bottle of Coca Cola contained 12 teaspoons of sugar, and asked whether a parent would be happy giving that much to their child.

Soft drinks manufacturers retaliated with their own adverts, urging politicians to reject the tax, claiming that jobs would be lost in their industry and in sugar production, which is important in Mexico. They said that small shops, dependent on soft drinks sales, would close and linked the campaign to former New York mayor Michael Bloomberg's anti-obesity drive. “Michael Bloomberg, [former] mayor of New York, has financed with $10m a health campaign against sweetened drinks. He wants to do in Mexico what he could not do in New York,” said the adverts.

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