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The weight of the world: Researchers weigh human population

Humanity could stand to lose a few pounds.

If the entire human population stepped on a scale, the weight would be 316 million tons, or 632 billion pounds, a new study finds.

The overweight people in the world carry a total of 16 million tons of extra weight — that's the equivalent of 242 million normal-weight people. Obese people carry 3.8 million tons of extra weight, the equivalent of 56 million normal-weight people.

"Everyone accepts that population growth threatens global environmental sustainability — our study shows that population fatness is also a major threat," said study researcher Ian Roberts, of the London School of Hygiene and Tropical Medicine.

The energy requirement of any species depends not only on the number of individuals in its population, but also on its total mass: the more mass people in the world have, the higher their energy needs will be, the researchers said.

Roberts and colleagues used 2005 estimates of the world's population in their analysis. They also obtained information about the average body mass index (BMI) of people in each country, and calculated the percentage of the population that is overweight and obese.

The average body mass, globally, was 136 pounds (62 kilograms.) In North America, which has the highest average body mass of any continent, the number was 178 pounds (80.7 kg).

North America has only 6 percent of the world's population, but 34 percent all the human biomass in the world that is due to obesity, the researchers said. In contrast, Asia has 61 percent of the world's population, but only 13 percent of the world's biomass due to obesity.

If all countries had the same average BMI as the United States, the total human biomass would increase by 63 million tons (58 million metric tons), equivalent to the weight of 473 million people, the researchers said.

The study is published today (June 17) in the journal BMC Public Health.

Pass it on:  The human population weighs about 316 million tons.

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