America is no longer the fattest of the world's more populous countries. That inglorious title now belongs to Mexico, according to a report [PDF] published last month by the United Nations.

In 2008, 32.8% of Mexican adults were obese, compared to 31.8% of American adults.

(A tiny island in the South Pacific called Nauru still tops the list as the world's fattest country, with an adult obesity rate of 71.1%).

The rise in obesity rates is not surprising as more Mexicans move into wealthier, urban areas, meaning more fast food choices and less time spent exercising.

"American-sized" portions, soda, and other junk foods are overtaking traditional Mexican fare.

The nation's poor are at an even greater risk of becoming obese.

"The same people who are malnourished are the ones who are becoming obese," Physician Abelardo Avila, a researcher at Mexico's National Institute of Medical Science and Nutrition, told the GlobalPost. "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."

A recent estimate revealed that 10 million Mexicans, one-sixth of the adult population, suffers from diabetes linked to over-eating and little exercise.