We've heard that marriage, office snacks and even our house clutter can make us fat, but now experts claim even fresh air can cause us to pile on the pounds.
Danish scientists have found a link between increasing levels of obesity and carbon dioxide in the air.
Researchers from the Glostrup University Hospital studied the weight of both overweight and slim people over 22 years.
They discovered that thinner people were putting weight for no reason and pinpointed a correlation between CO2 concentration and weight gain.
“The normal theory is that fat people get fatter because they don’t move as much as they should,” explains Lars-Georg Hersoug in the Science Nordic journal.
“But the study showed that thin people also get fatter, and this happened over the whole of the 22-year period of the study.”
The study, in association with the University of Copenhagen, tested six young men to see how CO2 levels affect their appetite. Half of the men were exposed to increased amounts of CO2 and the rest in a normal climate.
After seven hours in the assigned room, the men were allowed to eat as much as they liked.
The researchers found that men with greater levels of CO2 in their blood ate 6% more food than those who had breathed in a normal amount of CO2.
Hersoug concluded that orexins – the hormones in the brain that influence energy expenditure and food intake – are affected by CO2. So much so, it alters the metabolism and makes people gain weight.
“We could also see that the extra CO2 caused their heartbeat’s to rise, and this gives us the indication that CO2 affects the brain’s nerve cells – orexins in the hypothalamus – which among other functions, control our appetite,” explains Hersoug.
The theory behind this is because breathing in CO2 makes the blood more acidic which subsequently affects our brain so we want to eat more.
However, researchers added that their findings was not an excuse to ditch outdoor 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,” explains Hersoug.