Increasing global obesity to US level equates to an extra half a billion people in food energy demand

BMJ 2012; 344 doi: (Published 19 June 2012) Cite this as: BMJ 2012;344:e4255
  1. Susan Mayor
  1. 1London

Growing levels of overweight and obesity could have the same implications for world food energy demands as an extra half a billion people living on the earth if all countries reach the current fatness profile of the United States, warns a modelling study published this week.1

People’s weight, not just population size, should be taken into account when planning how to deal with increasing pressure on the planet’s dwindling resources, say the researchers.

“Everyone accepts that population growth threatens global environmental sustainability. Our study shows that population fatness is also a major threat,” said the lead author, Ian Roberts, professor of epidemiology and public health at the London School of Hygiene and Tropical Medicine. “Unless we tackle both population and fatness our chances are slim.”

The amount of energy humans need as a species depends not just on the total number in the population but also on the average mass of each person. To assess this, the research group used population estimates for 2005 from the United Nations population database to calculate the total energy requirement for each country in the world. They also calculated the proportion of each national population that is overweight (body mass index >25) and obese (BMI>30) on the basis of World Health Organization figures and estimated the biomass resulting from overweight and obesity for each country.

Overall, global adult human biomass was approximately 287 million tonnes, 5% of which (15 million tonnes) was due to overweight and 1.2% (3.5 million tonnes) to obesity.

North America accounts for only 6% of the world population but has 34% of the biomass from obesity, with the highest average body mass of any continent (80.7 kg). In contrast, Asia has 61% of the world population but 13% of the biomass from obesity.

The research group calculated that if all countries had the BMI distribution of the US, the increase in human biomass, 58 million tonnes, would be equivalent in energy requirements to that of an additional 473 million adults of average body mass living on the earth.

Increasing mass means higher energy requirements, because a bigger body burns more energy at rest and needs more energy to move.

“The concept of biomass is rarely applied to the human species,” said Roberts. “But the ecological implications of increasing body mass are significant and ought to be taken into account when planning for future resource challenges. Before the population was fat, it made perfect sense to plan based on how many mouths to feed. As the population has got fatter, we are not feeding mouths—we are feeding flesh. So the demand on food supplies is how much flesh we have to feed.

“We tend to see fatness as a personal health problem, with the locus of responsibility on the individual. But we see fatness as a political problem with the locus of responsibility as a collective issue. This not about obese individuals but about fat populations, with the average body mass shifting upwards.

“Tackling population fatness may be critical to world food security and ecological sustainability. And the major determinant of population fatness is use of fossil fuels: sitting still and travelling by motorised transport. Decarbonisation is the solution,” he concluded.


Cite this as: BMJ 2012;344:e4255