• 03.19.12

CO2 Is Why You’re Fat

As the atmosphere fills with more carbon dioxide, it might mean that breathing creates a chemical reaction that makes you want to eat more. And more. And even more.

There is no single factor that has caused widespread obesity in the U.S.–though Co.Exist has compiled a list of potential reasons, including diet soda, driving, your mom, your job, and your fork. If you’d like, you can also blame CO2.


The theory: Neuropeptide hormones called orexins trigger energy expenditure and wakefulness in the body. They also play a role in stimulating food intake. When we breathe increasing levels of CO2, our blood becomes more acidic. This in turn affects orexins, which make us want to eat more. In layman’s term, that means the more CO2 is in the atmosphere, the hungrier you’re going to be.

The Danish scientists involved in the CO2 and obesity research stress that this has not been proven definitively, but they have tested out the theory. Last year, the researchers put six men at the University of Copenhagen in different “climate rooms,” some of which contained increased amounts of CO2. After being cooped up for seven hours, the men were given the opportunity to eat as much as they wanted. The men with higher levels of CO2 in their blood ate 6% more food than those who had normal levels of CO2.

This is an extremely small-scale study. And while it’s true that obesity levels have risen in tandem with CO2 levels, there is no real way to link the two. Still, it’s an intriguing hypothesis.

The researchers say that this doesn’t mean we should give up on exercise. “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,” said Lars-Georg Hersoug, one of the study’s researchers, in an interview with ScienceNordic.

Next, the researchers plan to test their theory with rats. If the hypothesis ends up being correct, climate change mitigation could get a whole new group of supporters who wouldn’t otherwise care about whether the planet is warming. But don’t hold your breath–that will just cause more CO2 to build up in your blood, anyway.

About the author

Ariel Schwartz is a Senior Editor at Co.Exist. She has contributed to SF Weekly, Popular Science, Inhabitat, Greenbiz, NBC Bay Area, GOOD Magazine and more.