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The saying may be “you are what you eat.” But for people in cities with higher levels of air pollution, it’s also what you breathe that could sabotage your waistline and affect your health.

A team led by Associate Professor of Molecular Medicine, Genetics, Immunology and Microbiology Kezhong Zhang has discovered why people living in areas with heavier concentrations of air pollution are at increased risk of developing metabolic disorders such as non-alcoholic fatty liver disease, type 2 diabetes and atherosclerosis.

A 2013 study pinpointed the stress mechanism that causes air pollution to impair lipid and glucose metabolism and insulin action in the liver. In 2015, the same group discovered that air pollution has direct effects on triggering liver fibrosis, a pathological condition characterized by accumulation of the extracellular matrix protein collagen that occurs in most chronic liver diseases.

The U.S. Environmental Protection Agency considers airborne particulate matter one of the six most common air pollutants and one of two most threatening to overall health. PM2.5 is airborne particulate matter with an aerodynamic diameter smaller than 2.5 micrometers — about one-tenth the diameter of a human hair. PM2.5 is a mix of particles and gases from gasoline and diesel engines, together with dust from roads, tires and brakes. The first breakthrough from Zhang’s group related to PM2.5 came in 2010, when it demonstrated that exposure to “real-world” air particulate causes cellular stress, including endoplasmic reticulum stress and oxidative stress in the liver and lung tissues.

“Our study indicated that those who work under high levels of PM2.5 exposure, such as truck drivers and car industry employees, have a much higher risk of developing metabolic diseases such as fatty liver disease and type 2 diabetes,” Zhang said. “The ongoing work could have a major impact on health policy decision-making as well as clinical disease diagnosis and treatment.”

Manufacturing employees, truck drivers and others experiencing long-term daily road traffic should pay close attention to blood markers or liver enzymes that indicate metabolic disease.

“According to our findings, these individuals should adjust their diets and lifestyles to reduce the risk caused by air pollution,” Zhang said.

He suggested a diet high in antioxidants, especially berries, beans, broccoli and spinach.

The research was funded by the National Environmental Health Science Institute (grant Nos. ES017829, ES018900, ES016588, ES017412) and the National Institute of Diabetes and Digestive and Kidney Diseases (grant No. DK090313).