• 03.08.16

The Smog In Your City Is Why You’re Fat

Lab rats living under Beijing’s air pollution put on the pounds.

The Smog In Your City Is Why You’re Fat
Nineteen days in, rats living with air pollution were 15% fatter.

If you walk around Beijing on a particularly smoggy day, you might end up with a sore throat and a cough. Stay longer, and things get worse: the city’s air pollution has been linked to everything from lung cancer and asthma to heart disease in residents. Now there’s some new evidence that living with filthy air might also make you fat.


In a recent experiment, baby rats breathing unfiltered Beijing air ended up as much as 18% heavier than rats living in a nearby cage with a filter. The rats all lived in a lab a little over a mile from a polluted 14-lane wide highway; one group got soot-filled air directly from outside, while the others had a HEPA filter to keep out the worst pollution.

At the beginning of the experiment, pregnant rats in both groups were basically all the same weight. Nineteen days in, those unlucky enough to live with air pollution were 15% fatter, with inflammation in their lungs and signs of insulin resistance. When their babies were born, they also gained weight quickly; the female babies were 10% heavier than the ones living in the filtered cage, and the male babies were 18% fatter.

Of course, a rat study doesn’t prove that the same thing would happen in people, though past studies have suggested a link between air pollution and childhood obesity in humans.

Junfeng Zhang, a professor of global and environmental health at Duke University and senior author of the paper, is hoping that the study might convince people to care more about air pollution. If long-term health fears aren’t enough, maybe vanity about their weight can help. After reading the results, “I hope they would be more supportive to policies and lifestyle changes–e.g., driving less and using air purifiers indoors–that would help improve air quality,” he says.

About the author

Adele Peters is a staff writer at Fast Company who focuses on solutions to some of the world's largest problems, from climate change to homelessness. Previously, she worked with GOOD, BioLite, and the Sustainable Products and Solutions program at UC Berkeley.