S u m m a r y :
Food packaging might be interfering with the functioning of intestines, preventing the adequate absorption of nutrients in humans, suggests a new study published in the journal Food and Function.
The Culprit: Zinc Oxide Nanoparticles
Canned food packaging sometimes comes with linings made of nanoparticles of zinc oxide; the latter is used because they preserve the food from microbes, and they prevent the staining of foods containing sulphur. However, they appear to have harmful effects on the intestines: they may be affecting nutrient absorption in humans by interfering with the process of absorption in the intestines, says the new study conducted by a team of researchers from Binghamton University, New York. These negative effects might also extend to gene expression as well.
“We found that zinc oxide 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 study author Gretchen Mahler.
100 Times More Zinc in Packaging
Mahler and her team analysed canned corn, tuna, asparagus, and chicken with a mass spectrometer to determine the amount of zinc oxide nanoparticles that might be making their way into the food. According to the findings, a substantial quantity becomes incorporated in it: around 100 times more than the daily recommended dietary allowance of zinc.
If the figures show such a great disparity between what is required and what is present in the food, could this excess zinc be adversely affecting the body, wondered the researchers. They, thus, looked into the consequences of these particles on the digestive system.
“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,” clarifies 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.”
Losing Intestinal Microvilli
Mahler explains that the nanoparticles cling onto the cells of the gastrointestinal tract where they modify the shape of microvilli, the minute projections found on the surface of the intestines meant to enhance the nutrient absorption; in some cases, the zinc oxide also accounts for the loss of microvilli. So, when the microvilli are affected, the absorption of nutrients decreases. Moreover, the nanoparticles, when in high concentrations, can also lead to pro-inflammatory signalling, thereby making the intestines more permeable, which then results in unwanted compounds entering the blood from the intestines.
Though the team has outlined the effects of the nanoparticles, they have not determined the long-term consequences.
“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,” says Mahler. “What I can say is that 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.”
“We have seen that our cell culture results are similar to results found in animals and that the gut microbial populations are affected. Future work will focus on these food additive-gut microbiome interactions,” adds Mahler.