Mexico has knocked the U.S. off its hefty pedestal to claim the title as the World's Fattest Developed Nation, according to a new United Nations Food and Agricultural Organization report.

The report found that 32.8 percent of Mexican adults are now obese. That's a slightly chubbier obesity rate than the 31.8 percent listed for Americans.

Fat Forecast: 42 Percent of Americans Will Be Obese by 2030

These statistics don't quite jibe with World Health Organization estimates, which, using different analysis techniques and time periods, put the level of obesity of Americans and Mexicans at 34 percent and 24 percent respectively. But there's no doubt the two countries have a growing problem. A recent Organization for Economic Co-operation and Development report found that, although the rise in obesity rates has slowed in many developed countries over the past three years, they increased by 4 to 5 percent in the U.S. and Mexico.

Mexico's rampant obesity rates come as no shock to experts, who have long warned that the Latin American country is turning into a vast "Waist Land."

More than 30 percent of Mexicans are now obese. Credit: Ronaldo Schemidt/AFP/Getty Images.

"As more Mexicans move from rural to urban communities they become more sedentary and they eat a steady diet of unhealthy, highly caloric foods," said Martin Binks, an obesity researcher who is a spokesman for the Obesity Society.

Binks said this is particularly true for less affluent Mexicans, who have limited budgets and little access to leaner fare such as fish, low fat grains and fresh fruits and vegetables. He said researchers are witnessing the same fattening process in Latinos, who move to the U.S. and live in urban, less affluent circumstances.

Obesity Is Big Business

The global shift from farming to a couch potato lifestyle now affects a frighteningly large portion of the world's population. WHO statistics show that more than 1.4 billion adults around the globe, ages 20 and older, are overweight. Of these more than 200 million men and nearly 300 million women are obese. Nearly 65 percent of the world's population lives in countries where being overweight or obese kills more people than being underweight.

More than 20 percent of the world's population is classified as obese, a condition the Centers for Disease Control and Prevention defines as a body mass index of greater than 30.

However, neither Mexico nor the U.S. comes close to winning the overall world's heavyweight title. That distinction belongs to the tiny island of American Somoa, where a whopping 75 percent of citizens are obese, and an additional 20 percent are merely overweight. By 15 months of age, more than 40 percent of boys and 30 percent of girls from the island nation are already overweight or obese, a Brown University study found.

Many of the slimmest nations are located in Asia. Less than 1 percent of the population in Vietnam and Laos is obese. Indonesia, Korea and Japan also boast obesity rates of less than 5 percent, though most experts agree that with increased industrialization, these numbers will probably climb.

"As Western culture permeates the globe, we see increases in obesity rates," Binks said. "Our metabolic profile is not really well suited to an environment where physical activity is limited and highly caloric foods are so readily available."