Increasing levels of obesity could have the same impact on overall energy demand as an extra 500 million people on the planet, according to new research that warns that tackling obesity may be critical to delivering global food security and environmental sustainability.

Researchers from the London School of Hygiene & Tropical Medicine today published the results of a study on the impact of increasing body mass index (BMI) on global energy and food demands.

Green groups and scientists are calling for ministers gathering at this week’s Rio+20 Earth Summit to take action to curb both population growth, which is expected to rise from around seven billion currently to up to 11 billion by 2050, and over-consumption of resources.

However, the new research from the School of Hygiene & Tropical Medicine warns that excessive food consumption can have as big an impact on energy demand as the size of a population.

Increasing mass means higher energy requirements, because it takes more energy to move a heavy body, the report states.

Using 2005 data from the United Nations and World Health Organisation, the researchers estimated the adult human population weighs in at 287 million tonnes, 15 million of which is due to people being overweight and 3.5 million of which is due to obesity.

North America recorded the highest average body mass of 80.7kg, compared to the global average of 62kg. The report concluded that the US held six per cent of the world’s population but 34 per cent of the world’s biomass mass, largely due to record levels of obesity.

The researchers estimated that if all countries had the same average BMI as the USA, the total human biomass would increase by 58 million tonnes, the equivalent of an additional 935 million people with average levels of body mass.

This increase corresponded to the energy requirements of about 473 million adults of current world average body mass.

In contrast, Asia has 61 per cent of the world’s population but only 13 per cent of the world’s biomass due to obesity.

The researchers found that if all countries had the same average BMI as Japan’s score of 22.9, total biomass would fall by five per cent, the equivalent of 235 million fewer people on the planet.

Japan and the USA were used to compare future scenarios because both are high income countries with adequate nutrition, but have completely different average BMI values.

Professor Ian Roberts, who led the research at LSHTM, urged decision-makers to consider weight as well as population size when planning how to deal with the dwindling global resources.

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