Previously, the United States with an adult obesity rate of 31.8 percent was the world's fattest nation. Last year, the percentage of U.S. adults overweight went down slightly.
A report by the FAO said Mexico's widely available inexpensive junk food and penetration of U.S. fast-food chains combined with a more sedentary lifestyle all contributed to Mexico's bulging waistline.
About 70 percent of Mexican adults are overweight, while childhood obesity tripled in a decade and about a third of teenagers are overweight as well, the Global Post said.
Weight-related diabetes claims 1-of-6 one of Mexican adults -- or 70,000 people a year -- suffering from the disease each year, the report said.