Danish researchers have recently announced a new theory as to why people all over the world are getting fatter – rising carbon dioxide levels are causing weight gain.

The study began years ago, when Danish post-doctoral researcher Lars-Georg Hersoug noticed some trends while going over MONICA (Monitoring of Trends and Determinants in Cardio-vascular Disease) statistics in Denmark. Hersoug found that both fat and thin people gained weight, with the same proportional increase, over the span of the 22-year study. Hersoug, of the Research Centre for Prevention and Health at Glostrup University Hospital, went on to point out that “the normal theory is that fat people get fatter because they don’t move as much as they should. But the study showed that thin people also get fatter, and this happened over the whole of the 22-year period of the study.”

Hersoug’s studies show that obesity development was highest in the east coast area of the U.S. between 1986-2010, where C02 concentrations were the highest. Another study from 2010 showed that 20,000 animals including dogs, cats, mice and monkeys from various labs put on weight, regardless of a controlled diet. “The probability that all animals of eight different species put on weight from random causes is one in 10,000,000,” states Hersoug. And the most compelling evidence supporting the CO2 theory came in 2007, when a study revealed that the pH value of blood, its acidity, affects nerve cells called orexins.

Orexins, which are neuropeptide hormones, exist in the brain and stimulate wakefulness and energy expenditure. These hormones may be affected by CO2, and this can cause a person to go to bed later, which in turn affects metabolism, making it easier to put on weight. But orexins are also involved in the stimulation of apetite.

One might wonder what the point of exercise might be if the air is making us fat anyway, but Hersoug says that physical activity is still worthwhile. “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.” Hersoug adds that eating fruits and vegetables also brings down the pH levels in the blood, so a healthy diet is still a good idea.

Interestingly, Hersoug suggests that living in the mountains might also help one to lose weight, as CO2 levels are lower in higher elevation. One might consider using this lung-powered iPhone charger while running in the mountains, to shave off some extra pounds.