Tuna might not be so good for us after all

People rarely have a bad word to say about tuna; it’s an oily fish packed with vitamins, and it’s pretty cheap.

But alas; it turns out that it also contains something less good for your gut, as new research published in the journal Food & Function suggests it could contain more zinc than is good for us.

This isn’t because fish are swimming around with it in their insides, but because it’s commonly used to line the inside of cans.

Apparently, zinc could be leeching into our food and altering our ability to absorb nutrients.

Consuming high doses of zinc can reduce the amount of copper the body can absorb, for example, potentially leading to anaemia and weakening of the bones.

Researchers analysed cans of tuna, asparagus, sweetcorn and chicken. These were all chosen as they’re known to be pretty low in zinc, but packaged in tins that are lined in the mineral.

Results suggested that tuna tin linings, and the fish at the centre of these cans, are contaminated with more than 5,000 ppm of zinc.

Juices at the bottom of the can, meanwhile, had around a third of the metal contamination as the food that was touching the tin.

Tinned chicken was the second-most contaminated food, followed by asparagus – which had around two thirds of the zinc levels of tuna – then sweetcorn.

Study author Professor Gretchen Mahler from Binghamton University, New York, told MailOnline: “We found zinc oxide nanoparticles at doses that are relevant to what you might normally eat in a meal or a day can change the way your intestine absorbs nutrients or your intestinal cell gene and protein expression.

“[Nanoparticles] 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.

“This loss of surface area tends to result in a decrease in nutrient absorption.

“Some of the nanoparticles also cause pro-inflammatory signalling at high doses and this can increase the permeability of the intestinal model.”

She said that an increase in intestinal permeability “not a good thing” and that it could mean that compounds that are not supposed to pass through the bloodstream could be able to.

Mahler stressed, however, than these results are based on the mineral’s affect on cells grown in a laboratory rather than in humans.

She added: “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.”

Are you willing to give up tasty, tasty tuna just in case?

For more information on zinc intake, visit the NHS website.

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