MEXICO CITY — Soft drinks are so deeply embedded in the diet here that they have become part of the dining tradition, from the taco stand to the white- linen restaurant. Whether lunch consists of corn tortillas and beans, or meat in sauces infused with cacao and fragrant spices of Aztec origin, it usually goes with something fizzy.

And sugary.

The seemingly unquenchable thirst for soda in Mexico has made the soft drinks industry economically and politically powerful; a former president, Vicente Fox, rose to prominence as a Coca-Cola executive.

But that thirst has also contributed to an obesity epidemic. Looking for a way to attack the problem two years ago, the Mexican government consulted public health experts and imposed a national tax of about 10 percent on sugary drinks.

The tax turned Mexico, where more than 70 percent of adults and a third of elementary school children are overweight, into an international experiment. The idea was to see whether raising the price of soft drinks would encourage consumers to switch to healthier beverages.