By By Lauren Streib

No matter how you tip the scales, Americans are getting wider every year. What's worse is that many nations are following suit.

In a list of the countries with the greatest percentage of overweight people, Nauru tops a list of countries with the greatest percentage of overweight people, with an alarming 94.5 percent of its adult population (ages 15+) classified as such, based on the most recent estimates by the World Health Organization (WHO). The Federated States of Micronesia, Cook Islands, Niue and Tonga round out the top five, all with a portly population of over 90 percent.

The U.S. weighs in at No. 9, with 74.1 percent of those over 15 years old considered overweight. But given that its population is nearly 20,000 times that of Nauru, clearly the U.S.'s size belies it rank.

Experts say it is not surprising that people across the globe are increasingly becoming overweight. They blame urbanization and the influx of Western ways of life including myriad fast-food choices, little exercise and stressful jobs.

"Due to urbanization, more people are living in more dense environments, in cities where they are removed from traditional food sources and dependent on an industrial food supply," says Neville Rigby, director of policy and public affairs for the International Association for the Study of Obesity. Modernization is causing countries with small populations and few resources to depend on imported, often over-processed food. "The Western diet overwhelms, and many people are not genetically engineered to cope with this," says Rigby.

Countries transformed

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In the last 50 years this area has established significant economic ties with the U.S. and New Zealand, which caused a surge in Western imports and a significant change in diet. Studies conducted by the WHO Western Pacific regional office and by the International Obesity Task Force, a London-based think tank, also point to several other factors they say contribute to the region's high obesity rates. These include the common belief that beauty is marked by a large physical size, the reliance on fatty, nutrient-deficient imported foods and a decrease in activity caused by less farming and agricultural work.

Elsewhere, developing countries are dealing with what many experts call a nutrition transition - economies that are used to dealing primarily with undernutrition must now fight obesity.

"Obesity has become a problem of poverty," says Daniel Epstein of the WHO Regional Office of the Americas. "Poor people have an easier time of eating junk food. People fill up on things that have a high caloric value but little nutritional value."

Dr. Frank Hu, associate professor of nutrition and epidemiology at Harvard School of Public Health, agrees.

China and India have relatively low percentages of overweight adults, 28.9 percent and 16 percent respectively. But obesity and its potential complications are increasing there at unparalleled speed due to the growth of urban populations and an expanding middle class who can afford richer food in greater quantities than their rural counterparts. In China, for example, the number of obese people has tripled since 1992, the WHO reports.

It's not all about size
The related health risks associated with being overweight are striking. Cardiovascular disease, type 2 diabetes, hypertension and stroke are just some of the hazards.

It should not come as a shock that the nation with the highest rate of adult diabetes is Nauru, where nearly 31 percent of the population is struck with the disease, according to the International Diabetes Federation. The countries with the largest numbers of people with diabetes are India (40.9 million), China (39.8 million) and the U.S. (19.2 million).

Behind the numbers
The WHO's definitions of "overweight" and "obese" are based on an individual's body mass index (BMI), which measures weight relative to height. Overweight is marked by a BMI greater than or equal to 25 and obese is defined as having a BMI greater than or equal to 30.

It's important to note that the definitions for overweight can vary by country and study. For example, in China, where the population has a high susceptibility to abdominal obesity (which is not directly reflected in BMI calculations), the cut-off point for overweight is 23.

There are currently 1.6 billion overweight adults in the world. In just 10 years, the WHO projects that number will grow by 40 percent.

As far as comparing the obesity rates of countries, "it's hard to make automatic comparisons," says Rigby. "It's more important to recognize that levels are increasing across the board."