Globally, obesity accounts for about 1.6% of all greenhouse gas (GHG) emissions, according to the results of a study headed by researchers at the University of Copenhagen. The extra burden of GHG emissions includes CO2 production from increased metabolic processes, and emissions relating to higher food intake (and so requirement for increased food production), and fossil fuels used for transporting both food, and heavier people. The scientists, reporting their results in Obesity, calculate that in total, obesity could contribute to an extra 700 megatons per year of CO2 equivalent (CO2eq), which is more than the total GHG emissions of nations such as Australia or Korea, and about the same as total GHG emissions from Canada or Mexico.

“Our analysis suggests that, in addition to beneficial effects on morbidity, mortality, and healthcare costs, managing obesity can favorably affect the environment as well,” said Faidon Magkos, PhD, of the department of nutrition, exercise, and sports at the University of Copenhagen in Denmark. “This has important implications for all those involved in the management of obesity.” Magkos is corresponding author of the researchers published paper, which is titled, “The Environmental Foodprint of Obesity.”

All oxygen-dependent organisms on the planet produce CO2 as a result of the metabolic processes that are necessary to sustain life. So, total CO2 production by any species is linked to the average metabolic rate, the average body size, and the total number of individuals of the species. This means that continued growth of the human population can be seen as “a major determinant of global GHG emissions,” the scientists noted. This impact of human population size on GHG emissions is compounded even further if the average size of the average person also continues to grow. “Here we argue that a further challenge will be the body weight of the average person on the planet and the increasing number of people with obesity,” the team continued. “This argument draws from the fact that the energy requirement of any species, including humans, is a function of the number of organisms (i.e., population size) and their average mass (i.e., body weight).”

The researchers now report on calculations that approximate how much extra greenhouse gas emissions might be due to a person being obese, rather than of normal weight. Because the primary greenhouse gases, CO2, methane, and nitrous oxide, all have different global warming potential and longevity in the atmosphere, a measure of CO2eq is used enable comparisons between them.

Obesity impacts on GHG emissions in a variety of ways. Most directly, studies have shown that people with obesity produce more carbon dioxide from oxidative metabolism, than do individuals of normal weight. “Individuals of normal body weight with a metabolism of 9,000 kJ/d produce about 260 mL/min of CO2 on average during a 24-hour period, which is equivalent to ~270 kg/y of CO2,” the investigators stated. “CO2 production (and oxygen consumption) is higher in individuals with obesity compared with lean individuals, consistent with their greater total daily energy expenditure … Assuming a more realistic average of 30% greater total energy expenditure in people with obesity compared with lean people during a typical 24-hour period, the extra CO2 emissions by one individual with obesity would be approximately 81 kg/y of CO2eq.”

Put into global perspective, obesity could feasibly be responsible for excess metabolic CO2 emissions of some 49 megatons (Mt) of CO2eq/year. That’s equivalent to the total fossil CO2 emissions of an entire Scandinavian country such as Sweden, Finland, or Denmark, or to the metabolic CO2 emissions of 183 million people of normal weight, the team noted. In fact, this direct effect of “accelerated” metabolism in people with obesity may be considered a relatively small additional CO2 emission burden, when compared with global figures, the scientists continued. Rather, “the indirect effects due to food consumption and transportation are quantitatively much more important.”

Maintenance of greater body weight requires the consumption of increased amounts of food and drink, and so the production and transportation of more food for consumers. “The growing proportion of the population with excess body weight influences food and drink consumption because the higher energy expenditure of these individuals causes a proportionate increase in energy requirements to maintain their greater body weight,” the investigators pointed out. “Individuals with obesity consume, on average, ~30% more energy from food and drinks to match their higher energy expenditure and maintain their greater body weight. Accordingly, this gives rise to an increase in CO2, CH4, and N2O emissions from food, crop, and livestock production. Similarly, transportation of heavier people is associated with increased consumption of fossil fuels. This results in additional greenhouse gas emissions related to food production and transportation processes. “ … transporting heavier passengers is expected to raise GHG emissions,” the researchers noted.

“Transport accounts for about 14% of total GHG emissions,” they said. “ … obesity can be expected to increase GHG emissions from automobile and air transportation by 476 kg/y of CO2eq per person. This corresponds to an increase by ~14% over the emissions associated with the transportation of a normal-weight person.”

In summary, the researchers say their calculations suggest that compared with a normal-weight individual, a person with obesity is “responsible” for an extra 81 kg/year of CO2eq from higher metabolism (7% total), an extra 593 kg/y of CO2eq from greater food and drink consumption (52% of total), and an extra 476 kg/y of CO2eq for car and air transportation (41% of total).” The total equates to about 20% more than the total emissions attributed to a lean person.

The authors acknowledged that their calculations are just estimates. Also, they pointed out, it not just obesity that impacts on GHG emissions. People who are more physically active need more food than sedentary people, and so metabolic CO2 production, and GHG emissions associated with food production are also comparably higher for these individuals.

The investigators emphasized that it is “critically important” not to use the new data to increase weight stigmatization. People with obesity already suffer from negative attitudes and discrimination, they noted, and numerous studies have documented evidence indicating that this stigmatization can make individuals with obesity more vulnerable to health risk behaviors and outcomes that can exacerbate poor health and obesity, such as binge eating, overeating, avoiding exercise, and increased stress.



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