Now air pollution is causing you to gain weight


Mastering control over one’s weight is an ongoing process. Everyone’s body is a little different, and weight fluctuations can be brought on by a myriad of factors like genetics, exercise habits, and of course, diet. Moving forward, we all may have to add another element to the weight watching discussion: polluted air.

It’s well known that smog can cause a litany of health problems, from cardiovascular issues to even mental health symptoms like depression. On the heels of a new study conducted by the University of Colorado at Boulder, it looks like polluted air can also induce weight gain. Just another reason to buy that farm out in the country and escape city life.

So, how exactly does dirty air promote extra pounds? It messes with our gut bacteria, increasing one’s risk of obesity, diabetes, gastrointestinal disorders, and a variety of other chronic health problems.

This study is quite noteworthy; it’s the first-ever to find a reasonable connection between smog and detrimental changes to the human gut microbiome. Just in case you were unaware, “gut microbiome” refers to the trillions of microscopic organisms relaxing in your stomach as you read this. It sounds disgusting at first, but take comfort in the fact that those stomach stowaways are keeping you healthy.

The study’s authors were motivated by Denver, Colorado’s local source of air pollution, the aptly named “brown cloud.” They found that young adults who had spent considerable time exposed to smog showed less microbial diversity in their guts. Just that observation alone is concerning. The more variety of microorganisms present in one’s stomach the better. On top of that, their guts also displayed higher levels of bacterial species associated with obesity and disease.

“We know from previous research that air pollutants can have a whole host of adverse health effects,” says senior author Tanya Alderete, an assistant professor of integrative physiology, in a press release. “The takeaway from this paper is that some of those effects might be due to changes in the gut.”

On a global scale, the US is in pretty good shape when it comes to air pollution. There are many countries whose residents are exposed to more harmful levels of smogs regularly (China, India, Poland). Still, air pollution is unavoidable to some degree in any urban environment. Moreover, pollution levels in the US appear to be on an upswing. Portions of New Jersey, New York, California, and Texas, just to name a few, have already been penalized by the EPA for high levels of air pollution. 

If you’re still not convinced that smog is a real problem, consider this: according to research published just this month smog causes 8.8 million deaths each year. That’s more than cigarettes or war on an annual basis.

While the majority of research has focused on smog’s effect on respiratory function, there have been signs that it influences the stomach. For instance, research has shown that hospital visits for stomach problems tend to spike on especially smoggy days.

So, in an effort to better understand smog’s effect on the gut, the research team used a state-of-the-art whole-genome sequencing technique to analyze fecal samples from 101 young adults living in the Southern California area. Data from air-monitoring stations near participants’ homes were also analyzed to calculate how much air pollution each person had been exposed to over the past year.

Three variations of air pollution were considered; ozone (usually from car emissions), particulate matter (harmful dust suspended in the air), and nitrous oxide (from burning fossil fuels). Among those three, ozone seems to have the most effect on the gut, accounting for 11% of the gut bacteria variations seen in participants. To put that in perspective, that means the ozone influenced their gut bacteria more than gender, diet, and ethnicity. 

Those who were exposed to high levels of ozone had less overall diversity among their gut bacteria.

“This is important since lower (bacteria) diversity has been linked with obesity and Type 2 diabetes,” Alderete explains.

Additionally, lots of exposure to ozone was linked to higher amounts of certain bacteria linked to obesity. In total, over 120 other bacteria types appeared to be changed by exposure to ozone. These species impact a variety of bodily processes associated with weight, such as insulin release and metabolite production.

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

The study’s findings, while preliminary, make a strong argument that smog can cause weight gain. The research team is already planning a more extensive follow-up study that will focus on young adults living in Denver.

“A lot of work still needs to be done, but this adds to a growing body of literature showing that human exposure to air pollution can have lasting, harmful effects on human health,” Alderete concludes.

These revelations serve as a reminder of just how influential our living environment is to our wellbeing, even when we don’t realize it. Regarding maintaining an ideal weight, perhaps a healthy regiment of fresh air should be added to diet and wellness plans, especially for urban residents.

The full study can be found here, published in Environment International.