And if you were to add us all up, we'd weigh more than eight million tractor trailers put together.

How much do 6.8 billion people weigh? Far too much, according to a new study released today by researchers at the London School of Hygiene and Tropical Medicine.

All told, the world's population clocks in at 287 million metric tons (or 316 million Imperial tons). By comparison, a fully loaded tractor trailer in the United States weighs around 36 metric tons, meaning you'd need to stack almost 8 million of them on top of each other to reach the same weight. And all that body mass is taking a toll on the earth's available resources, the scientists say.

North Americans account for an astonishing share of the world's body mass -- 34 percent, to be exact, despite making up only 6 percent of the world's population. In Asia, you get the opposite picture: the continent supports a majority of the world's population -- 61 percent -- yet is responsible for just 13 percent of global human biomass.

Of course, those numbers mask deep inequalities in global access to nutrition. Inhabitants of developed countries are the most well-fed, and are the best equipped to pay for food. Meanwhile, much of the developing world remains undernourished, and as nutrition improves, we can only expect pressure on the world's food supply to grow.

In fact, the researchers claim, if all the countries in the world had a weight distribution like the United States, we'd see an explosion in the number of obese people worldwide. If you divided all that extra weight into 62-kilogram chunks -- the average body mass of a single global citizen -- you'd wind up with 935 million extra people wandering around on the planet.

Here's a graphical representation of the scientists' hypothetical, drawn from data collected in 2005:

The big data point here is China, whose obesity rates are literally off the charts in this imaginary scenario.

Until now, we've generally thought of overpopulation in terms of numbers of people on earth, with milestones for 5 billion, 6 billion, and so on. But one of the paper's authors suggests that measure may soon be superseded -- or at least rivalled -- by the sustainability of our growing waistlines.

"We do not move our bodies so much but we are biologically programmed to eat," he told the Daily Telegraph. "We often point the finger at poor women in Africa having too many babies. But we've also got to think of this fatness thing; it's part of the same issue of exceeding our planetary limits."