We know that homemade meals are usually more nutritious than the fries-burger-soda combo from your nearest fast food outlet. But that’s not the only reason cooking your own food is the healthier bet: Research suggests those quickly-delivered burgers could contain some pretty long-lasting chemicals.

A study released Wednesday by the Silent Spring Institute found that eating out, especially at fast food and pizza chains, corresponded with higher bodily levels of PFAS — also called “forever chemicals” because they don’t break down under normal environmental conditions — than eating at home.

PFAS (or per- and polyfluoroalkyl substances, if you prefer long, science-y words) are a broad class of chemicals that have been linked to a number of adverse health effects, including cancer. Once you’ve ingested them, be it through contaminated water, food, or air, PFAS can linger in your body for weeks or even months.

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They’re also all over the place — scientists have found PFAS in everything from chocolate cake to artificial turf. An individual’s level of bodily PFAS depends on what they eat, the products in their home, and if they have the misfortune of living near a contaminated water supply. But on a population level, food is thought to be people’s main source of PFAS.

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Laurel Schaider, an environmental chemist who studies human’s exposure to these toxic compounds and a co-author of the study, says that PFAS end up in our food one of two ways: through the food itself, if plants or livestock were raised with contaminated soil or water, or from the food’s packaging. PFAS can be added to paper to make it grease-resistant, and are found on around half of fast food containers — including those compostable takeout bowls.

Schaider and her team compared levels of PFAS in participants’ blood with their reported diet over the last day, week, month, and year. Since the compounds can take months to leave your system, “PFAS in your body represents a cumulative exposure over a really extended period of time,” Schaider said.

Given the prevalence of the compound in fast food packaging in particular, her team’s findings make sense: People who reported regularly consuming more calories at home (made with food from grocery stores) had lower levels of PFAS in their blood than people who ate out at fast food restaurants. The different time intervals included in the study let researchers see the impact of what a person habitually eats on their PFAS levels, as opposed to whether consuming a particular food once had a measurable effect.

While it’s not great that there are toxic chemicals rubbing off on our french fries, there are some hopeful takeaways we can glean from the study. “The good news,” said Schaider, “is that our findings suggest that there are things we can do in our daily lives to reduce our ingestion of PFAS from our food.” Namely, eating more food cooked at home.

But that doesn’t necessarily get to the root of the problem. “We can’t rely on consumers to shop their way out of this challenge,” Schaider said. “When they take their family out to dinner … they’re not thinking about toxic chemicals being in their food.”

Federal regulations seem unlikely under the current administration — over the summer, two officials from the FDA issued a statement saying that “based on the available current science, the FDA does not have any indication that these substances are a human health concern.” And while some state and local governments are banning products containing PFAS, it might be a good idea in the meantime to skip the drive-thru for a homemade dinner.