Tying together two of the most controversial topics of our time is a study which links rising carbon dioxide (Co2) levels to the so-called obesity epidemic. To be polemical, the greenhouse gas most often pointed to as the major contributor to global warming and climate change is making waistlines swell around the world. The research is the work of Danish researcher Lars-Georg Hersoug, who used data from a 22-year-long study on weight gain and heart health, and it could drastically change how we talk about these two issues. However, it could just be a classic case of correlation and not causation.
In his research published in the journal of Nutrition and Diabetes, Hersoug drew from the Monitoring of Trends and Determinants in Cardio-vascular Disease study which kept tabs on the health of thousands of Danes for over two decades. He saw that though overweight people continued to put on weight, that “skinny” people did the same. To him, this ruled out the belief that an overweight lifestyle is a sedentary cycle that leads to more weight gain — after all, it wasn’t just the overweight people that were adding pounds.
Hersoug hit upon the idea that the rapid rise in Co2 levels in that same time frame might have contributed to the across the board weight gain. A 2007 study showed that increased Co2 levels makes blood more acidic, which in turn can affect the neuropeptide hormones called Orexins. These hormones help regulate the body’s sleeping and waking cycles. When they go out of whack, people stay up later which in turn wreaks havoc on their metabolism, causing people to eat more.
So now we’ve looped in bad sleeping habits, as well.
Backing his theory are other studies that show increased weight gain across numerous other species apart from humans in the same time frame. To test his theory, Hersoug exposed six men to increased Co2 levels for seven hours and then observed that they ate far more afterward. Additionally, Hersoug comments that the amounts of Co2 in beer might be responsible for creating beer guts in regular imbibers.
While this is an extremely interesting study, it does raise a few red flags. First of all, a six person experiment is hardly a comprehensive one, and one wonders how researchers could control for variables with so small a sample size. That makes the experiment seem rather anecdotal. Secondly, the basis of the theory — that Co2 rose with weight — also seems rather tenuous. What Hersoug may have found was that increased industrialization means higher fat foods entering the global food chain, more sedentary leisure activities (almost all of which, from large-scale sporting events to video games — require large amounts of electricity, most of which comes from carbon-producing processes), continued deforesting of Co2-sucking trees, and so on, all of which contribute to fatter people and higher Co2.
Fortunately, Hersoug does not paint his study as the be-all end-all for obesity in the modern age. Rather, a hypothesis that should encourage further study. Thankfully, he also does not advocate that reducing the body’s Co2 levels alone will lose weight, rather that increased activity and a healthy diet will purge C02 as well as helping to shave off extra pounds. He tells ScienceNordic:
“If you’re out running, you get your blood circulating and you can pump much of the CO2 out of your body, so our hypothesis is really further evidence that exercise is healthy. And exercise may be even more necessary in the future, when we can expect even higher CO2 concentrations in the atmosphere.”
While Hersoug’s work is enticing in its completeness, the adage that “extraordinary claims require extraordinary evidence” certainly holds. It’s going to take further studies and a boatload of supporting to research to make these kind of claims work, which Hersoug says he’s interested in doing. The next step for him will be research in mountainous areas, where Co2 concentrations are lower.
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