Obese people generate an extra 700 million tons of carbon dioxide per year than those with 'normal weight', according to a new study.

Research from The Obesity Society has revealed that obese people account for about 1.6 per cent of all man-made greenhouse gas emissions.

This is due to a combination of higher metabolic rates and the environmental impact of both producing the food and the increased fuel required to transport obese people, according to the researchers.

The society used greenhouse gas emission data, demographic data, and obesity prevalence statistics to estimate that obesity is responsible for 20 per cent more greenhouse gas emissions compared with people of a normal weight.

Researchers found an obese person produces an extra 81 kilos of carbon dioxide a year

WHAT IS OUR METABOLISM? Obesity has previously been linked to higher oxidative metabolism – the set of chemical reactions in our sells that use oxygen to convert food to energy. All oxygen-dependent organisms on the planet, from humans to microscopic bacteria, produce carbon dioxide as a result of metabolic processes necessary to live. Total carbon dioxide production from any species is linked to average metabolic rate, average body size and the total number of individuals of the species. Advertisement

Increasing average body size of people on Earth may further challenge attempts to reduce man-made carbon dioxide emissions, they say.

'Our analysis suggests that, in addition to beneficial effects on morbidity, mortality, and healthcare costs, managing obesity can favourably affect the environment as well,' said Faidon Magkos, corresponding author of the paper and nutritionist at the University of Copenhagen in Denmark.

'This has important implications for all those involved in the management of obesity.'

To assess the impact of obesity on the environment, researchers calculated the extra emission of greenhouse gases – carbon dioxide, methane and nitrous oxide – from the increased oxidative metabolism, increased food production and consumption, and the increased fuel use to transport the greater body weight of people with obesity.

Researchers used the standard definitions of obesity – body mass index of greater than or equal to 30 kg/m2 – and normal weight – body mass index of less than 25.

Compared with an individual with normal weight, obese people were found to produce an extra 81kg per year of carbon dioxide emissions from higher metabolism, an extra 593kg per year from greater food and drink consumption and an extra 476kg per year from car and air transportation.

Globally, obesity contributes to extra greenhouse gas emissions of around 49 megatons per year of carbon dioxide equivalent (CO2eq) – a standard unit for measuring carbon footprints – from metabolic activity alone.

Meat production not only produces heat-trapping greenhouse gases but can be a contributor to obesity

Energy requirements of humankind, and subsequently worldwide food demand, are now expected to increase not only because of a growing population but also due to the increasing body weight generally, creating a vicious cycle where food production will go up.

Meanwhile, transportation of heavier people is associated with increased production of fossil fuels, resulting in more carbon dioxide emissions from food production and transportation.

Obesity is expected to increase greenhouse gas emissions from automobile and air transportation by 476 kg per year of CO2eq per person – up 14 per cent from the emissions associated with the transportation of a normal‐weight person.

But the authors urge that this new information does not lead to more weight stigmatisation, which can make overweight individuals become more vulnerable to risky behaviours such as binge eating.

'People with obesity already suffer from negative attitudes and discrimination against them, and numerous studies have documented several prevalent stereotypes, e.g., that individuals with obesity are lazy, weak‐willed, lack self‐discipline, have poor willpower, and are noncompliant with weight loss treatments,' the paper reads.

Nutritionist Boyd Swinburn, in the School of Population Health at the University of Auckland in New Zealand, has suggested that no one will think of stigmatising people who exercise for having a negative effect on the environment, despite physical activity also being associated with carbon dioxide production.

The research paper was published online in Obesity, the flagship journal of The Obesity Society.