New research in America says tinned tuna contains more than 100 times the safe limit of zinc which impedes our ability to absorb minerals and vitamins. Zinc is commonly used to line the interior of cans since it is anti-microbial in nature. Although zinc is found in a wide array of foods and is used by the body, overdosing on it can alter our ability to absorb nutrients.
Researchers say the leaching of zinc into the tuna also makes our gut more permeable, meaning that toxic substances have an easier time entering our bloodstream. Study author Professor Gretchen Mahler said, “An increase in intestinal permeability is not a good thing – it means that compounds that are not supposed to pass through into the bloodstream might be able to.” The condition is commonly referred to as leaky gut syndrome but it is not a recognised medical condition.
The study, conducted by Binghamton University, New York and published in the journal Food & Function, looked at tins of tuna, sweetcorn, asparagus and chicken because they are all naturally low in zinc before packing. Tuna touching the can had over 5,000 ppm while tuna in the center of the can had just about the same amount. Tinned chicken was second for contamination, while asparagus had two thirds the contamination of tuna and sweetcorn one third.
A lab model of the small intestine found that the zinc caused higher levels of inflammation causing the gut to become permeable. The study also found that transportation of glucose fell by three quarters and iron fell by one third. As the model was lab grown, Professor Mahler said the effects on long term health was unknown.