You exercise regularly, get good sleep, and make sure to eat a balanced diet… yet you still can’t seem to stay at a healthy weight.  Turns out that the problem may not be in what you’re putting in your mouth, but what you’re breathing into your nose.

What does your gut tell you?

A recent study by the University of Colorado Boulder is the first to link air pollution to changes in the structure and function of the human gut microbiome – the collection of trillions of microorganisms inside us. What it found is that young adults exposed to higher levels of ozone show more of a certain species of microbe linked with obesity and less overall microbial diversity.

Senior author of the study, Tanya Alderete, noted that “Ozone is likely changing the environment of your gut to favor some bacteria over others, and that can have health consequences.”

One of the health consequences may be food preferences

A USC study seems to show that exposure to traffic pollution during childhood makes adolescents 34 percent more likely to eat foods high in unhealthy trans fats, regardless of household income, parent education level or proximity to fast-food restaurants.

While the link may seem strange, there is research to back it up. The scientists cited data from a  2012 study that found that mice who were exposed to diesel exhaust while in utero consumed 14 percent more calories than mice who received filtered air.

How is the air causing all of these weight problems?

While scientists don’t know all the answers yet… they suspect that the same small particles that give city air its haze are triggering a cascade of reactions in our bodies. Breathing in those particles irritates the tiny, moist air sacs that are meant to let oxygen into the bloodstream.  The irritation sends the lungs’ lining into overdrive, causing it to release hormones that mess with the body’s system for controlling blood sugar levels. This disturbance may also trigger immune cells to invade healthy tissue and interfere with our appetites.

The results are especially concerning for kids

Andrew Rundle at Columbia University conducted a study in the Bronx in which he had pregnant mothers wear a backpack to measure the air quality as they went about their daily life. After the children were born, their health was monitored for seven years. Controlling for other factors (such as wealth and diet), the children born in the most polluted areas were 2.3 times more likely to be considered obese, compared to those living in cleaner neighborhoods.

And indoor air is often an even bigger problem

According to the Environmental Protection Agency, indoor air is often two to five times more polluted than outdoor air.  Breathing in this low quality air can play a significant role in unhealthy weight gain, especially if there are smokers in the home.

A study conducted by the Medical College of Georgia at Augusta University showed that kids who were exposed to smoking had bigger bellies and more overall body fat.

How can we make sure that our air quality isn’t affecting our weight?

Obviously, living outside of a densely populated urban area is the best way to ensure that your air is low in pollutants that may cause weight gain, but that isn’t an option for everyone.  City dwellers should check the pollution forecasts before spending too much time outdoors and try to take advantage of green spaces as often as possible. To ensure that your indoor air is clean of harmful pollutants, consider purchasing a high-quality air purifier.