The U.S. obesity crisis is no secret - people around the country are getting fatter and it's costing us billions.

But obesity isn't just an American issue. According to a study published in the journal BMC Public Health this week, it's also a global health issue... and not for the reason you may think.

Researchers at the London School of Hygiene and Tropical Medicine used data from the United Nations and the World Health Organization to estimate the total mass of the human population. In 2005 we, as a global society, weighed approximately 316 million tons, which is about 17 million tons overweight.

Obesity caused 3.9 million tons of that total, the equivalent of 56 million average-sized people. Even more concerning: North America accounts for only 6% of the world's population but 34% of its obesity-related mass.



"One tonne of human biomass corresponds to approximately 12 adults in North America and 17 adults in Asia," according to the study. "If all countries had the BMI distribution of the USA, the increase in human biomass ... would be equivalent in mass to an extra 935 million people." (There's about 2,200 pounds in one tonne, and 2,000 pounds in a ton).

So North Americans are fatter than people living in Asia, you might be thinking. What's the big deal?

The problem, the researchers say, comes when you relate that number to the amount of food needed to keep those "extra 935 million people" alive. And while some people may be obese, "everyone is getting fatter," study author Ian Roberts wrote in an e-mail.

The energy requirements for the human species depends on the total number of people and our average mass. Heavier people need more energy, or food.

And if the heavier people also have more money, any lack of food resources would be felt more by the world's poor.

"We need to be clear that overconsumption in the wealthy world is a problem for personal and planetary health," Roberts wrote. "Fatness is a political issue that needs urgent attention. The fact that the average American is overweight - with one third of the population obese - is not a trivial problem and should be considered at the United Nations."