Researchers find surprising reason for weight gain

Breathing dirty air takes a heavy toll on gut bacteria, boosting the risk of obesity, diabetes, gastrointestinal disorders and other chronic illnesses, according to new research.

Thestudy 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 residing within us.

The gaseous pollutant ozone is particularly hazardous, the study found, with those exposed to higher levels of ozone showing less microbial diversity and more of certain species associated with obesity and disease.

“We know from previous research that air pollutants can have a whole host of adverse health effects,” said senior author Tanya Alderete, an associate professor of integrative physiology, pointing to studies linking smog with Type 2 diabetes, weight gain and inflammatory bowel diseases. 

“The takeaway from this paper is that some of those effects might be due to changes in the gut.”

According to research published this month, air pollution kills 8.8 million people worldwide each year – more than smoking or war.

While much attention has been paid to respiratory health, Assoc. Prof. Alderete’s previous studies have shown pollution can also impair the body’s ability to regulate blood sugar and influence the risk for obesity. 

Other research has shown visits to emergency rooms for gastrointestinal problems spike on high pollution days.

To investigate just what might be going on inside the gut, Assoc. Prof. Alderete’s team used cutting-edge whole-genome sequencing to analyse faecal samples from 101 adults in California.

The researchers looked at data from air-monitoring stations near the subjects’ addresses to calculate their exposure in the previous year to ozone (which forms when emissions from vehicles are exposed to sunlight), particulate matter (hazardous particles suspended in the air) and nitrous oxide (a toxic by-product of burning fossil fuel).

Of all the pollutants measured, ozone had the greatest impact on the gut by far, accounting for about 11 per cent of the variation seen between study subjects – more of an impact than gender, ethnicity or even diet. Those with higher exposure to ozone also had fewer varieties of bacteria living in their gut.

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

Subjects with higher exposure to ozone also had a greater abundance of a specific species called Bacteroides caecimuris. That’s important, because some studies have associated high levels of Bacteroides with obesity. 

In all, the researchers identified 128 bacterial species influenced by increased ozone exposure. Some may have an impact on the release of insulin – the hormone responsible for ushering sugar into the muscles for energy. Other species can produce metabolites, including fatty acids, which help maintain gut barrier integrity and ward off inflammation.

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

The study was relatively small and has some limitations, including the fact that stool samples were taken only once.

Do you think pollution can have an impact on your weight? What is the air quality like where you live?

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Written by Ben

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