The question of whether carbon dioxide should be considered a pollutant under the Clean Air Act and regulated by the Environmental Protection Agency has been a political football for the past decade.

In 1998, the Clinton administration decided that it was, but in 2003, the Bush administration reversed this policy. And in 2007, the Supreme Court split things down the middle, ruling that the EPA had the authority to regulate emissions of greenhouse gases but was possibly not required to do so.

All of that took place within the context of the contentious argument over global warming. But now there is a new charge against carbon dioxide that may strike more deeply at the heart of American public opinion: The claim that it promotes obesity.

That is the conclusion of Danish researcher Lars-Georg Hersoug, who examined 22 years worth of data on weight gain in Denmark and found that skinny people showed proportionately as much weight gain as those who were already overweight. This suggested to him that the cause must lie not in lifestyle but in some more general factor, a possibility supported by data showing eight different species of laboratory animals also gaining weight despite being fed a controlled diet.

But why blame CO2? The evidence here is more circumstantial, but Hersoug notes that atmospheric levels of the gas have risen during the same period and that in the United States, obesity has increased most rapidly on the East Coast, where CO2 concentrations are highest.

Hersoug has so far conducted just one test of his hypothesis, an experiement in which six young men were placed in special climate rooms for seven hours. They were then given the opportunity to eat as much as they wanted, and those who had been exposed to increased CO2 levels ate six percent more than those who had not.

Hersoug believes that hormones in the brain are affected by CO2 and may in turn alter our appetite and metabolism. He also suggests that CO2 in beer may be to blame for beer bellies and recommends spending more time outdoors, eating plenty of fruits and vegetables, and engaging in vigorous exercise to pump excess CO2 out of the bloodstream., which reported on the study, notes that Hersoug's single small-scale experiment should be considered more anecdotal than scientific. Fortunately, however, Hersoug appears more than ready to continue his research.

Photo by Dori (Own work) [GFDL ( or CC-BY-SA-3.0-us (], via Wikimedia Commons