In a country that claims to lead the world in childhood obesity, a soda tax appears to be working.

A year after Mexico levied a one-peso tax on sugary drinks in January 2014, relevant soda purchases had decreased by 12%, according to a study published this week in the BMJ. The tax had an even greater impact on low-income buyers, whose purchases of taxed beverages dropped more than 17% within the year. When the tax was first enacted, one of the study’s co-authors, University of North Carolina professor Barry Popkin, told Politico that expected that the tax would decrease soda consumption by 5%.

The Mexican Legislature created the world’s largest soda tax experiment when they designed the tax, as well as a similar one on high-calorie foods, in response to a growing obesity epidemic. In 2012, Coca-Cola ko found that Mexico was its favorite country, with the average Mexican drinking 728 cans of Coca-Cola products per year—almost 8 times the worldwide average.

It’s an experiment that’s been closely watched by policymakers and public health advocates in the United States—including former New York mayor Michael Bloomberg, who reportedly contributed $10 million toward Mexico’s plan—who have long argued over the effectiveness of such measures.

But the jury is still out on whether a decline in soda purchases will lead to a healthier Mexico, in which 70% of adults are overweight or obese. As a 2014 study by a health economist at the University of Wisconsin—Madison found, soda taxes are correlated with a decrease in sugary drink purchases, but it’s not clear that they dent overall calorie intake.