Much of the debate surrounding global population growth and the expected 2 billion extra people on the planet by 2050 — when the United Nations (UN) estimates that 8.9 billion of us will be competing for space, resources and nutrition — has focused on sheer numbers.

The size and weight of the population — crucial considerations given the varying human biomass depending on the country you live in — has not been much in focus.

Until this year, that is, when during the summer the London School of Hygiene and Tropical Medicine raised this point about the species’ energy requirements depending on its average mass. A report led by the school’s Professor Ian Roberts used data from the UN and the World Health Organization (WHO) 2005 SuRF 2 report to calculate the world’s human weight and level of obesity.

The findings, published in BioMed Central’s open access journal BMC Public Health, estimated the average body mass globally to be 62 kg, and the global adult human population to weigh 287 million tonnes.

Somewhat surprisingly, a relatively small 15 million tonnes of this aggregate mass is owing to the overweight and 3.5 million tonnes to obesity, but this is because the heaviest nations tend to be the richest.

North America has the highest body mass: with only 6% of the world’s population, it has 34% of the world’s biomass mass, as a result of obesity. The average US body mass index (BMI) in 2005 was 28.7. Asia, with 61% of the world’s population, accounts for only 13% of the world’s biomass as a result of obesity.

The top 10 heaviest nations also include two European countries, Croatia (3rd) and Greece (9th). In another measure, Russia, Germany and the UK are in the mid-single digits — and therefore very high up the scale — in terms of the percentage of national biomass accounted for by people with a BMI of over 30 (obese).

Professor Roberts issues a stark warning: ‘Population fatness is a major threat. Unless we tackle both population and fatness, our chances are slim.’

French life sciences consultancy Alcimed backs this contention with its own study: globally, one in three people is overweight and one in 10 obese. Obesity rates have doubled in the 32 years since 1980, and in 2008, 1.5 billion people were overweight. France, long perceived as a country and culture with neither a prevalence of, nor fear about, fatness, is now being seen as a medium worry: 48% of men and 37% of woman are at least overweight, says Alcimed.

The WHO says obesity is avoidable, a point that governments have taken up with alacrity, variously launching mobility/active life programmes (Let’s Move, US; Change4Life, UK; Actionsant, Switzerland; and Vivons en Forme, France); partnering with agro-food enterprises on stressing nutritional values; and introducing tax measures that aim to limit fat, sugar and salt intake. However, such taxes are contentious, as it is difficult to precisely define cause and effect, as far as food consumption is concerned, believes Alcimed agro-food business director Florent Surugue.