Here’s a stomach-churning fact to go with your breakfast: as many as one in five meat products might contain DNA from an animal not mentioned on the label.

BBC News unearthed this figure by filing a Freedom of Information request to the Food Standards Agency (FSA) in the UK. Out of 665 meat products gathered from restaurants and supermarket in England, Wales, and Northern Ireland in 2017, the FSA reported that at least 145 were partly – in some cases, totally – made up of unspecified meat.

DNA analysis showed that some meats contained up to four different species of animal in the product, despite there being no mention on the labeling. The most common contaminant was cow DNA, followed by pig, chicken, sheep, and then turkey. Lamb was found the most commonly contaminated type of meat, followed by beef and goat. The most commonly offending “problem foods” were mincemeat, sausages, kebabs, restaurant curries, ready meals, and burgers.

It's also worth noting that only half the of local authorities in the UK actually submitted samples to the FSA's Food Surveillance System.

The FSA guidelines suggest that any meat product containing over 1 percent DNA of another unlabeled animal should be considered an active attempt to scam consumers. At some point along the supply chain, somebody made the decision to mislabel their product and replace expensive meat with a cheaper alternative.

While this study only looked at meat in the UK, it’s likely to be only the beginning of the story. Last year, a study found that over 25 percent of fish sold in US retailers was mislabeled as the wrong fish.

In this case, it’s speculated that producers are knowingly aware they are selling on cheaply farmed or high-mercury fish, like tilapia or tilefish, as desirable top-shelf fish, such as tuna and snapper. The analysis shows that just 9 percent of products labeled as snappers were actually snappers.

It isn’t even just animal products that could be tricking you. A public document by the UK FSA explains that food fraudsters regularly misrepresent the authenticity of products such as olive oil, honey, and alcohol. That expensive bottle of olive oil might say “extra-virgin first pressing,” but that might not necessarily be what’s inside.