Scientists finally measured the shocking percentage of fast food that contains harmful chemicals

For the first time, researchers have measured meals at major fast-food chains like McDonald’s, Chipotle, and Taco Bell for the presence of a harmful group of chemicals called phthalates, and their findings aren’t inspiring. The study—published today in the Journal of Exposure Science & Environmental Epidemiology by researchers at George Washington University’s Milken Institute School of Public Health—reports that the vast majority of items they collected contained the chemicals.

Phthalates are endocrine-disrupting chemicals widely used in cosmetics, vinyl floors, detergents, disposable gloves, wire covers, and—for years now—food packages. They make plastic supple and bendable, which is why they’re so ubiquitous. But they’re also linked to a risk of serious health ailments, including reproductive problems, asthma, and brain impairment in kids. The EPA estimates that nearly 500 million pounds of phthalates are produced every year, meaning most people’s bodies contain at least low levels of the compounds.

In recent years, other work by these Milken Institute researchers has identified fast food as a worrisome probable source of phthalate exposure. In 2018, for example, they looked at urine samples for some 10,000 Americans nationwide and found the ones who reported eating at fast-food restaurants were likely to have higher levels of phthalates than people who ate at home.

Their latest research, though, is the first to examine the food itself. The paper describes that they collected 64 menu items from San Antonio-area locations of McDonald’s, Burger King, Pizza Hut, Domino’s, Taco Bell, and Chipotle. The phthalate DBP was present in 81% of the items, while 70% contained DEHP. (Both of these are linked to fertility problems.) The foods with meat were the worst—chicken burritos and cheeseburgers generally had the highest concentrations of these chemicals, while cheese pizza and French fries had the lowest levels. Researchers collected the disposable gloves worn by workers too, and the chemicals also showed up in them. Finally, nearly 90% of food items contained another plasticizer (DEHT) that was invented to replace phthalates, though research hasn’t established yet whether DEHT is safer. (“It is not clear,” according to a 2018 study, “whether DEHT fits the designation of ‘acutely toxic’ under the Federal Hazardous Substances Act.”)

The Milken Institute team’s position has for years been that evidence supports home-cooked meals transmit lower levels of these bad chemicals, probably because nobody cooks or handles food in home in gloves, and most of the ingredients involve less plastic packaging. Their latest study reiterates once again that the best way to reduce exposure is simple: Eat fast food less often.

We reached out to the companies included in the study and will update this post if we hear back.