Researchers say that increasing levels of fatness around the world could have the same impact on global resources as an extra billion people, BBC News said.

The team estimated the total weight of people on the planet and found that North America had the highest average.

Although only 6% of the global population live there, it is responsible for more than a third of the obesity.

The research is published in the journal BMC Public Health. In their report, the researchers from the London School of Hygiene and Tropical Medicine calculate the weight of the global population at 287 million tonnes. They estimate that 15 million tonnes of this mass is due to people being overweight, and 3.5 million tonnes due to obesity.

Using World Health Organization data from 2005, the scientists worked out that the average global body weight was 62kg (137lb). But there were huge regional differences. In North America, the average was 80.7kg (178lb), while in Asia it was 57.7kg (127lb).

While Asia accounts for 61% of the global population, it only accounts for 13% of the weight of the world due to obesity.

One of the authors of the paper, Prof Ian Roberts, explained the thinking behind the calculation. "When people think about environmental sustainability, they immediately focus on population. Actually, when it comes down to it - it's not how many mouths there are to feed, it's how much flesh there is on the planet."

The scientists also compiled tables of the heaviest and lightest countries according to their estimates.

The U.S., with its well documented problems with weight, is top of the list. If the rest of the world were to emulate the Americans, Prof Roberts says, it would have dramatic implications for the planet.

While countries like Eritrea, Vietnam and Ethiopia are at the other end of the scale from the U.S., the researchers argue it is not sufficient to say that being skinny is just a factor of poverty. The researchers point to a country like Japan which, according to Professor Roberts, could be a model for others.

But other countries in the top 10 most weighty are more of a surprise, and include Kuwait, Croatia, Qatar and Egypt.