Lose Weight to Go Green

The newest target of the worldwide “Go Green” campaign is obesity. Virtually everyone understands the concepts of reduce, reuse, and recycle in the context of being better stewards of the environment, but now “reduce” may mean reducing your waistline. An article recently published in the International Journal of Epidemiology, suggests that the prevalence of obesity in the population today significantly contributes to greenhouse gas emissions and climate change.

Of the nearly 7 million people on the planet today, more than 1 billion are overweight, and 300 million are obese. Of course, overweight and obesity contribute to numerous health concerns, including type 2 diabetes, cardiovascular disease, and cancer. But, do overweight and obesity cause global warming as well? The authors of the article say “yes.” They compared 2 hypothetical populations: one consisting of a “normal” adult population and one consisting of an “overweight” adult population. The “normal” population of 1 billion people had a mean body mass index (BMI) of 24.5 kg/m2 and 3.5% of the population was obese, having a BMI of greater than or equal to 30 kg/m2. (A BMI between 18 and 24.9 kg/m^2 indicates a healthy weight, and a BMI of 25 to 29.9 kg/m^2 indicates overweight.) The “overweight” population had a mean BMI of 29.0 kg/m^2 and 40% of the population was obese.  The normal population demographics were based on census data from the United Kingdom in 1970, and the overweight population reflects the predicted UK population in 2010.

Food production is estimated to account for 20% of global greenhouse gas emissions, and transportation accounts for 14%. Since food consumption is strongly correlated to increased BMI, and increased BMI leads to increased transportation energy expenditures, the authors assumed that a population with a higher average BMI would be a significant contributor to global climate change. Based on statistical modeling, the authors concluded that the overweight population required 19% more food energy than the normal population, leading to an additional production of 0.54 gigatonnes of carbon dioxide equivalents. (In 2000, the total global production of carbon dioxide equivalents was approximately 42 gigatonnes.) Considering transportation and food production, the total increase in carbon dioxide equivalents is estimated to be up to 1.0 gigatonnes each year for the overweight population.

Industrialized nations produce most of the world’s greenhouse gas emissions owing to increased food production and transportation. Further, most of the world’s overweight and obese people live in industrialized nations. The potential of what we eat and how we travel could, therefore, have significant environmental consequences. The world is moving from a plant-based diet to an animal-based diet, contributing significantly to chronic disease and obesity, but also environmental deterioration. However, is blaming overweight and obese people the best solution to a global crisis? The current epidemiological evaluation makes very broad assumptions about hypothetical populations to draw its conclusions. Body mass index is not an entirely reliable indicator of body fat content, as it relies only on height and weight to calculate fat content. This estimation is particularly unreliable in elderly people who lose muscle mass due to age, or in athletes with a muscular build. Last, the authors make no assertions that the 1.0 extra gigatonnes of carbon dioxide equivalents would have a significant impact on the total production of carbon dioxide equivalents. While every little bit helps in solving the environmental problems that face our planet — think globally, act locally! — is focusing on body size the best way to minimize our carbon footprint?

References

AKHTAR, A., GREGER, M., FERDOWSIAN, H., & FRANK, E. (2009). Health Professionals’ Roles in Animal Agriculture, Climate Change, and Human Health American Journal of Preventive Medicine, 36 (2), 182-187 DOI: 10.1016/j.amepre.2008.09.043

Dummer TJ. Health geography: supporting public health policy and planning. CMAJ. Apr 22 2008;178(9):1177-1180.

Edwards, P., & Roberts, I. (2009). Population adiposity and climate change International Journal of Epidemiology DOI: 10.1093/ije/dyp172

Haines A, McMichael AJ, Epstein PR. Environment and health: 2. Global climate change and health. CMAJ. Sep 19 2000;163(6):729-734.