Nope, it's not the cheeseburger, it's the air that's making you pack on the pounds.

A Danish study of weight-gain statistics over a 22-year period found that increased carbon dioxide in the air may be causing people to eat more and therefore may be making people fatter. Boiled down, the idea is that the pH value of our blood affects our nerve cells, and they affect how hungry we feel and our metabolism. When we breathe in more CO2, our blood becomes more acidic and we feel hungrier.

The study revealed that thinner people and fatter people were gaining weight at about the same proportion, indicating that environmental factors may be at work. Additionally, about 20,000 animals were studied to have gained weight even when given food under controlled conditions, further supporting the theory that the air may impact food intake.

Either way, CO2 levels in the U.S. are highest on the East Coast, where obesity rates have risen the highest over the past quarter century, according to the study. And we thought it was the Philly Cheesesteaks.