MEXICO CITY — Mexico put its schoolchildren on a diet at the beginning of the year. But as often happens with New Year’s resolutions, there are many ways to cheat. Here is some of what is allowed for sale in schools under new guidelines that are intended to combat childhood obesity: lollipops, potato and corn chips (in multiple guises), and cookies (complemented by marshmallow or chocolate filling).

But the message is getting through, sort of. Portions verge on the miniature; sugar is limited; the chips are baked, not fried; and soft drinks are banned in elementary schools.

“My doctor told me that I had to drink water to look after my health,” said Santiago Daniel Torres, a bulky 14-year-old. Gone are the grease-drenched sandwiches and fried pork rinds that he used to buy. “They banned them,” he said as classmates wandered by clutching foil packets of cookies and chips. “More water, that’s better.”

By all measures, Mexico is one of the fattest countries in the world, and the obesity starts early. One in three children is overweight or obese, according to the government. So the nation’s health and education officials stepped in last year to limit what schools could sell at recess. (Schools in Mexico do not provide lunch.)