Staying slim is good for the planet, according to two UK researchers who concluded that because food production has a big impact on global warming, a lean population such as that of Vietnam will eat nearly 20 per cent less food and produce fewer greenhouse gases than populations where 40 per cent of people are obese (close to that of the United States today).

The study was conducted by Drs Phil Edwards and Ian Roberts of the Department of Epidemiology and Population Health at the London School of Hygiene & Tropical Medicine, and appears in the advanced access April 19 issue of the International Journal of Epidemiology.

The average BMI (Body Mass Index, the ratio of a person’s weight in kg to their height in metres squared) of nearly every country in the world is going up. Between 1994 and 2004 in the UK this went up from 26 to 27.3 among men, and from 25.8 to 26.9 among women: the average adult in the UK is about 3 kg or half a stone, heavier. But this trend is reflected throughout the world: we are all gradually getting fatter.

More and more research is suggesting this rising global obesity problem affects not just public health but the environment as well, and Edwards and Roberts decided to work out what happens to greenhouse gas emissions as the body mass index (BMI) of a population rises.

They used an accepted set of equations called the Schofield equations to work out the amount of food energy that is needed to keep a basal metabolic rate in two hypothetical adult populations of men and women: one with a normal BMI distribution where only 3.5 per cent are obese, and one where 40 per cent of the people are obese.

These two populations reflect how the UK was in the 1970s and what it is predicted to be in the year 2010. Another way to see it is as Vietnam is today and nearly how the US is today.

They also worked out how much extra greenhouse gas would be produced from the heavier population using more transport fuel.

The results showed that:

  • Compared with a lean population with a normal BMI distribution, a population where 40 per cent of people are obese, would need 19 per cent more food energy.

  • If the more obese population were 1 billion people (about 15 per cent of the world), it would produce between 0.4 and 1.0 more gigatonnes of carbon dioxide equivalents per year than the lean population.

Edwards and Roberts concluded that:

“The maintenance of a healthy BMI has important environmental benefits in terms of lower greenhouse gas emissions.”

They said that:

“When it comes to food consumption, moving about in a heavy body is like driving around in a gas guzzler.”

“The heavier our bodies become the harder and more unpleasant it is to move about in them and the more dependent we become on our cars,” they added.

Keeping slim is good for both health and the environment, they said, suggesting that:

“We need to be doing a lot more to reverse the global trend towards fatness, and recognise it as a key factor in the battle to reduce emissions and slow climate change.”

“Population adiposity and climate change.”
Phil Edwards and Ian Roberts.
International Journal of Epidemiology Advance Access published on April 19, 2009.
doi:10.1093/ije/dyp172

Additional sources: London School of Hygiene & Tropical Medicine.

Written by: Catharine Paddock, PhD