Mexico has edged out the United States as the most obese country, according to the United Country's Food and Agricultural Organization.

The report says that about 32.8 percent of Mexican adults are overweight, compared to the U.S. figure of 31.8 percent. (Some small Pacific Island countries, like Nauru and the Cook Islands, have obesity rates twice as high as Mexico.) Over the past decade, childhood obesity has tripled in Mexico, with experts warning that four of five heavy children stay fat for their whole lives.

"The same people who are malnourished are the ones who are becoming obese," said physician Abelardo Avila with Mexico's Countryal Nutrition Institute. "In the poor classes we have obese parents and malnourished children. The worst thing is the children are becoming programmed for obesity. It's a very serious epidemic."

More than ever, Mexicans are eating processed foods like potato chips, which have helped to supplant a traditional Mexican diet of whole grains and vegetables.

Sodas and sugary drinks are a huge part of the reason behind Mexico becoming the fattest country, says Barry Popkin, an obesity expert from the University of North Carolina who says Mexicans drink more sugary drinks than any other country.

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