The whole population of the Earth weights 287 million tonnes, out of which obese and overweight people account for 18.5 million tonnes, found the British researchers from the London School of Hygiene and Tropical Medicine. They believe increasing weight should be taken into account along with increasing numbers when assessing the risk of using up the Earth's resources.

They calculated for the first time the weight of the world's population using data from the World Health Organization, which indicates that on average, an adult weighs some 62 kilos. In the US, an average adult weighs a third more- some 80 kilos. Asians are slimmer on average – 57.7 kilos. Even though around 61 percent of the world population lives in Asia, Asians only cover 13 percent of the world's weight.

“Everyone accepts that population growth threatens global environmental sustainability – our study shows that population fatness is also a major threat. Unless we tackle both population and fatness our chances are slim,” said Professor Ian Roberts, who led the research.

The US is given as a negative example. If all countries had the same average body mass index (BMI) as the US, the total human biomass would increase by 58 million tonnes. This would be the equivalent of an additional 935 million people of world average body mass.

Being fatter requires more energy, because it takes more energy to move a heavy body, which in turn puts pressure on the Earth resources.

“Our results emphasize the importance of looking at biomass rather than just population numbers when considering the ecological impact of a species, especially humans,” said Sarah Walpole, a hospital doctor who worked on the research.

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