Population fatness puts as big a pressure on world resources as numbers, and the global effect of overweight and obese people is like adding half a billion to the 7 billion humans on the planet, scientists revealed this week.
Looking at the planet’s distribution of human biomass and the effect of obesity, the researchers found that while North America is home to 6% of the world’s population, it is responsible for more than a third of global obesity.
Around half the food a human being eats is burned up in physical activity. But the more mass a person has, the more energy he or she needs for the same amount of physical activity, because it takes more energy to move a heavier body. Even when not moving, a heavier body burns more energy.
Writing in the 18 June online issue of BMC Public Health, researchers from the London School of Hygiene & Tropical Medicine (LSHTM) suggest tackling population weight is crucial for food security and ecological sustainability, because the energy demands of a species depends not only on numbers but also on its mass.
The study was led by Ian Roberts, Professor of Epidemiology & Public Heath at LSHTM. He told the press:
“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.”
Using data from the United Nations (UN) and the World Health Organization (WHO), Roberts and colleagues estimated that the weight of all the adult humans on the planet adds up to 287 million tonnes, and that 15 million of this is due to overweight and 3.5 million to obesity.
They also calculated how the mass of the human population is distributed by region around the world, and what proportion is due to overweight and obesity.
They found that the overall average mass of an individual adult human on planet Earth is 62 kg. But in North America, the average body mass is 80.7 kg. Moreover, while North America has only 6% of the world’s population, it has 34% of the total human biomass that is due to obesity.
This was in stark contrast to Asia, home to 61% of the world’s population, but responsible for only 13% of total human biomass due to obesity.
“One tonne of human biomass corresponds to approximately 12 adults in North America and 17 adults in Asia,” write the authors.
“If all countries had the BMI distribution of the USA, the increase in human biomass of 58 million tonnes would be equivalent in mass to an extra 935 million people of average body mass, and have energy requirements equivalent to that of 473 million adults,” they add, concluding that:
“Increasing population fatness could have the same implications for world food energy demands as an extra half a billion people living on the earth.”
Sarah Walpole, a hospital doctor who worked with the LSHTM team on the study, said the findings highlight “the importance of looking at biomass rather than just population numbers when considering the ecological impact of a species, especially humans.”
The researchers suggest their numbers could be on the low side because they used figures from the 2005 WHO SURF report. The UN predicts there could be 8.9 billion humans on planet Earth by 2050.
Written by Catharine Paddock PhD