Subway stands behind its chicken.

The sandwich chain is disputing the findings of a CBC Marketplace investigation into fast food chicken. While most of the samples were found to contain close to 100 per cent chicken DNA, Subway sandwiches contained substantially less than the other chains. Tests showed an average of 53.6 per cent chicken DNA for the oven-roasted chicken and 42.8 per cent for the chicken strips.

The story has garnered worldwide attention, and raised questions about how much chicken should be in a chicken sandwich.

Subway's oven-roasted chicken sandwich patty contains about 50 per cent chicken DNA, according to lab tests. (CBC) Subway says the report was "absolutely false and misleading," and demanded it be retracted. The Associated Press reported Tuesday that the chain says its sandwiches contain 100 per cent white meat with seasonings, although the ingredient list it provided to CBC News lists soy protein as a component of the company's chicken.

Marketplace stands by its report and is releasing the Subway test results as well as additional detail about the methodology and investigation.

Here's what the DNA testing means

The testing of chicken from McDonalds, Wendy's, A&W, Subway and Tim Hortons was conducted at a DNA lab at Trent University in Peterborough, Ont.

Marketplace initially tested three samples from Subway: two from the oven-roasted chicken and one from the chicken strips. Each piece of chicken was broken down into three smaller samples, which were individually tested. The lab also retested these samples a second time.

Since the results were so markedly different than the DNA composition of the other sandwiches, the lab tested 10 new samples, five of the oven-roasted chicken and five of the chicken strips. The samples were obtained from multiple locations across Southern Ontario.

The repeated tests all reinforced the lab's initial assessment. The results reported by CBC were the combined average of the results of all three tests.

The lab also tested the samples from all chains for plant DNA, and found that about half the DNA in the chicken samples from Subway were of plant origin, the majority of which was soy.

Only the Subway samples had significant levels of plant DNA.

A note about the test results: This was the information about the DNA lab testing that was provided to Subway on Feb. 16, 2017. The first batch of Subway samples was retested, and those numbers are reflected in our final percentages.

While many media outlets took the results to mean that the chicken is only half chicken, the reality of DNA testing is slightly more nuanced.

DNA tests don't reveal an exact percentage of the amount of chicken in the whole piece, but DNA experts have told Marketplace that the testing is a good indicator of the proportion of animal and plant DNA in the product.

Trent University's Wildlife Forensic DNA Laboratory stands by its test results.

Robert Hanner, a biologist and associate director for the Canadian Barcode of Life Network at the University of Guelph, Ont., said DNA results "cannot be taken as exact mass ratios in the product," but he adds they are a good indicator of how much soy is in Subway's chicken.

Benjamin Bohrer, a food scientist at the University of Guelph and meat processing expert, in a blog post published Monday, called for greater transparency from fast food companies so the public knows what they're eating.

"DNA tests do not lie (especially when conducted multiple times), and anyone with access to a DNA laboratory could perform these tests," he wrote.

"Either make your chicken truly a marinated, seasoned chicken OR embrace your products for what they are and tell your customers about your agenda. Consumers want to know the story of their food, so be transparent."

Here's what's in Subway chicken

Subway declined to speak with Marketplace on camera about the findings, and declined to show Marketplace where and how its chicken is made.

The chain did confirm, by email, the ingredients in its chicken:

Chicken strips : Boneless, skinless, chicken breasts, water, soy protein concentrate, modified potato starch, sodium phosphate, potassium chloride, salt, maltodextrin, yeast extract, flavours, spices, dextrose, onion powder, carmelized sugar, paprika, chicken broth, vinegar solids, paprika extract.



: Boneless, skinless, chicken breasts, water, soy protein concentrate, modified potato starch, sodium phosphate, potassium chloride, salt, maltodextrin, yeast extract, flavours, spices, dextrose, onion powder, carmelized sugar, paprika, chicken broth, vinegar solids, paprika extract. Chicken patty: Chicken breast meat, water, seasoning (sea salt, sugar, chicken stock, salt, flavours, canola oil, onion powder, garlic powder, spice, chicken fat, honey), soy protein, sodium phosphates.

Marketplace also reviewed ingredient lists for all of the other sandwiches tested, and none of them listed soy.