Zinc in canned goods can restrict nutrient absorption, study finds

10 Apr 2018 --- Zinc nanoparticles that are present in tinned foods may negatively affect how the digestive tract operates, as they are absorbed into the bloodstream, a study has found. Researchers at Binghamton University, State University at New York, found that the nanoparticles may decrease nutrient absorption in digestion, as well as bump up the levels of zinc in the food itself to 100 times the daily allowance. The long-term effect on human health is unknown and is something that warrants future research, the researchers state.

"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," said Gretchen Mahler, associate professor of bioengineering.

According to Mahler, these ZnO nanoparticles are present in the lining of certain canned goods for their antimicrobial properties and to prevent staining of sulfur-producing foods.

In the study, canned corn, tuna, asparagus and chicken were studied using mass spectrometry to estimate how many particles might be transferred to the food. It was found that the foods contained 100 times the daily dietary allowance of zinc. The researchers then looked at the effect that the particles had on the digestive tract.

“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.”

“They tend to settle onto the cells representing the gastrointestinal tract and cause remodeling or loss of the microvilli, which are tiny projections on the surface of the intestinal absorptive cells that help to increase the surface area available for absorption,” says Mahler.

“This loss of surface area tends to result in a decrease in nutrient absorption. Some of the nanoparticles also cause pro-inflammatory signaling at high doses, and this can increase the permeability of the intestinal model. An increase in intestinal permeability is not a good thing as it means that compounds that are not supposed to pass through into the bloodstream might be able to.”

Researchers indicate that they are unsure of what the long-term health effects may be on human health. However, Mahler does state: “Our model shows that the nanoparticles do have effects on our in vitro model, and that understanding how they affect gut function is an important area of study for consumer safety.”

The researchers are now looking at how an animal model (chickens) responds to nanoparticle ingestion due to similar cell structures in human and animals, regarding how the gut microbial populations are affected. However, “Future work will focus on these food additive-gut microbiome interactions,” Mahler adds.

The concern that particles from our food packaging are “contaminating” our food has plagued headlines in recent months in light of the New Orb Media discoveries. 

The recent study found potentially harmful plastic particles in the water bottles of 11 leading global brands, including Dasani (Coca-Cola), Epura (PepsiCo), Aqua (Danone) and Nestlé Pure Life and San Pellegrino (Nestlé). Exclusive testing was conducted on more than 250 bottles from nine different countries, with 93 percent found to have contained plastic debris the size of the width of a human hair, including polypropylene, nylon and polyethylene terephthalate (PET). Microplastics – as they are known – are classified as less than 5mm in diameter by the US National Oceanic and Atmospheric Administration.

Although the effects on human health in a long-term manner are still mostly unknown, the findings have ignited an industry-wide debate over plastic use, and perhaps prompted broader concern over the way in which packaging may rub off on our food. NutritionInsight has discussed the microplastics debate in a detailed recent report.