That title is taken from an article of the same name in the peer-reviewed International Journal of Obesity by Gryka, Bloom, and Rolland, themselves from the Centre for Obesity Research and Epidemiology in Aberdeen.
The International Journal of Obesity is not to be confused with the journal Obesity, nor the Journal of Obesity, nor Obesity Reviews, nor The European Journal of Obesity, nor Obesity Research, nor Obesity Management, nor any other of the half dozen titles focusing on this mysterious disease. (Also see this.)
Before we start: when reading obesity “studies” I am always put in mind of The Onion “story” in which busy doctors, worn thin by scurrying about, missing meals, treading hallways and stairways, are perplexed by their inability to discover the source of obesity.1
Anyway, Gryka and pals assembled together a whopping 25 fat folks with type-2 diabetes and stuck them on a “low-carbohydrate, high-protein diet” for six months. Having somebody breathing down your neck and pestering you to stop eating so damn much usually works, as far as diets go, and it worked here, too. The small sample of people lost an average of 10 kilograms (about 22 pounds).
Now it is true that if you were to haul around a 10-kilo weight you will expand more energy than if you did not, all else equal. Expending more energy means sucking up more oxygen, and thus expelling more carbon dioxide. A person with 10-kilo of extra stuffing around the short ribs will thus expel more CO2 than the same person grown svelter.
Therefore, ceteris paribus, fatter people will spew more CO2 than thin ones.
So much is not disputed, and is, in fact, indisputable. But from these simple truths, Gryka and pals conclude:
On the basis of the current data, for every 1 kg of body mass lost, the CO2 production would decrease 3.2 ml min-1. Therefore, an individual who lost 10 kg would produce 32 ml of CO2 less every minute. This would equal to 168 12 l (33.04 kg) of CO2 less in a year, compared with what would be produced without weight loss. In 2008, the global number of obese and overweight adults over 20 years old was 1.5 billion. If all those individuals lost 10 kg and sustained it for a year, the reduction in CO2 emissions would be 49.56 Mt CO2 per year. This would equate to 0.2% of CO2 emitted globally in 2007 by burning of fossil fuels and the manufacture of cement.
Whatever else we learn from this study, we at least are witness to the first researchers to equate human fat and cement production.
To measure CO2 exhalation, our scientists stuck people under a tent like that in the picture (the device is the Quark RMR). These measurements of course occurred in the lab and when the people were at rest (it is difficult to be vigorous lying in a bubble).
Actual CO2 will be very different for normal activities. Thus that 49.56 (and not 49.57 or 49.55) Megaton reduction is already dicey. That 32 ml per minute decrease in resting CO2 is for the very fat, but the authors assume it will be the same for the merely “overweight” and for those, fat or otherwise, without type-2 diabetes. The authors are aware of these criticisms and admit that their “calculations may be slightly overestimated.”
They do not however admit a weakness from the tiny, almost-not-there sample size. To extrapolate from 25 obese Scottish diabetics to the world population is not responsible.
Real uncertainties creep in with the ceteris paribus assumption. Things are anything but equal between a nation of grossly obese and another of thin folk. It costs CO2 to bring all that food to market for the fat nation, but all that “extra” CO2 that is saved in the thin nation is probably more than made up for in the CO2 not taken up by the food.
I mean that as food grows it stores CO2. Plants take it up directly, and our food animals eat the plants, storing more CO2. If people aren’t eating that food, we won’t grow it and therefore the CO2 that would have been taken up is left lingering in the air, trapping heat, and, as the authors say, causing “the extinction of many species, irreversible changes in the ecosystems and environmental disasters like storms, wildfires, droughts or floods.”
People are no different than food animals: they take up carbon because fat is made from carbon. Thus, since fat people store more carbon than thin, it might benefit our precious atmosphere to encourage more people to double dip their potato chips.
This analysis is no more speculative than that offered by our authors. Mine and theirs are probably both wrong, and wrong in ways that are unpredictable and unanticipated. The only difference between the two analyses is that mine does not pretend to posses scientific certitude.
1If anybody can find a link for this, please post it below.
Thanks to Willie Soon for forwarding the original article.