Canned foods: they’re sterile, safe, and last forever. The only problem is, a new study suggests, they may also keep our digestive tracts from absorbing key nutrients.

A specific component of cans may be causing the problem: zinc oxide, which has antimicrobial and anti-staining properties.

“We found that zinc oxide (ZnO) nanoparticles at doses that are relevant to what you might normally eat in a meal or a day can change the way that your intestine absorbs nutrients or your intestinal cell gene and protein expression,” says Gretchen Mahler, a bioengineer at Binghamton University, in the US.

Researchers used mass spectrometry to determine whether and how much zinc was transferring from containers into corn, asparagus, tuna and chicken canned goods. They found 100 times an individual’s daily required allowance of zinc was transferring from can to food to human. While this sounds like a lot, it’s a smaller amount than is usually examined.

“People have looked at the effects of nanoparticles on intestinal cells before, but they tend to work with really high doses and look for obvious toxicity, like cell death,” says Mahler. “We are looking at cell function, which is a much more subtle effect, and looking at nanoparticle doses that are closer to what you might really be exposed to.”

The team found zinc oxide nanoparticles tend to settle on gastrointestinal tract cells, causing the cells to remodel and lose their all-important microvilli — tiny projections on the intestinal lining that help in nutrient absorption. Over time, fewer microvilli can reduce nutrient absorption.

Furthermore, the nanoparticles, in higher doses, can also cause pro-inflammatory signaling, which may increase the permeability of the intestinal lining and allow molecules to seep into the bloodstream, where they are not meant to be.

The long-term implications to health aren’t clear, however. The researchers used cell cultures in a laboratory setting to test the effects of zinc oxide nanoparticles — a very different environment from a healthy human gut.

“It is difficult to say what the long-term effects of nanoparticle ingestion are on human health, especially based on results from a cell culture model,” said Mahler.

The study saw hints of an effect on the gut microbiome, but more research is needed to know for sure. The team aims to next analyze what happens in the guts of live animals, namely chickens, when they’ve ingested excessive zinc oxide nanoparticles.