Update, March 6: Subway has released the lab reports from both of its independent tests. Both Maxxam Analytics in Ontario, Canada and Elisa Technologies, Inc. in Florida used enzyme-linked immunosorbent assays (ELISA) designed for food products to quantify soy in the chicken. ELISA's are a standard type of assay that generally detect and quantify substances based on binding by an antibody. In the assay, antibody binding kicks off a detectable chemical reaction, commonly resulting in a color change. In the case of Elisa Technologies, the lab used an antibody that binds to soy flour proteins and the lab used known concentrations of those soy proteins for comparison to determine the quantity of soy protein in Subway's chicken samples.

In all samples, Elisa detected 3 parts-per-million or less of soy proteins, which is well below one percent of the chicken. Maxxam detected 5.3 ppm of soy protein in the chicken, which is still well below one percent.

Original story from March 3

Earlier this week, Ars reported that an investigation by the Canadian Broadcasting Corporation’s Marketplace revealed that Subway chicken may only contain 50 percent chicken, with the rest being mostly soy. But, in the fallout from the news, food scientists are scratching their heads at the CBC’s testing methods and interpretation.

“The CBC’s story would not dissuade me from getting a chicken sandwich at Subway if I wanted one,” Mary Ellen Camire, told Ars. Camire, who says she’s generally more partial to meatball subs, is a professor of food science and human nutrition at the University of Maine as well as the former president of the Institute of Food Technologists, a nonprofit, scientific society of food scientists.

Central to her skepticism is the CBC’s choice to use a DNA test from a lab not specializing in food science. (The CBC investigation used a wildlife research center at Trent University.) DNA tests are useful if you want to know, say, if the fish you’re buying at the store is the type of fish the store says it is, she explains. But food scientists typically don’t use DNA tests to look for proportions of content.

Joseph Marcy, the head of the food science and technology department at Virginia Polytechnic Institute and State University, agreed. “It seems like an unusual way to do that.”

For one thing, plant and animal cells vary in size and the amount of DNA content they carry. So DNA content alone would not be a good indicator of a substance's makeup without some extra calculations and tests. It’s conceivable that such cellular variation could be controlled for, given standardized substances to compare with, and results could be accurate after careful analysis. However, the CBC has not released the methods and calculations it used to analyze the raw DNA data.

Moreover, Camire says, Subway likely adds to its processed chicken a highly concentrated soy protein with yeast flavoring. This is a common binding and flavoring ingredient, and the manufacturer that makes Subway’s chicken provides similar chicken to other restaurants. With an artificial soy protein product like that, Camire wasn’t sure how much DNA would even be in it.

Last, if the chicken really was 50 percent soy protein, it would likely be very noticeable to those eating it. Soy protein would be much spongier and the chicken wouldn’t contain many protein fibers, Camire added. “I just don’t have a lot of confidence in the way that the testing was done,” she said.

Meanwhile, Subway has gone on the defensive, calling the tests “stunningly flawed” and releasing the results of independent analyses that indicate that the chicken in its restaurants only contains one percent soy or less—as the restaurant has always claimed. “Subway sent samples of the Canadian products that Marketplace claimed contained 50 percent soy protein to Maxxam Analytics in Canada and Elisa Technologies, Inc., in Florida," a Subway spokesperson said in a statement. "The results from both labs found soy protein below 10 ppm, or less than 1%, in all tested samples. These findings are consistent with the low levels of soy protein that we add with the spices and marinade to help keep the products moist and flavorful.”

Subway president and CEO Suzanne Greco was quoted as saying:

The stunningly flawed test by Marketplace is a tremendous disservice to our customers. The safety, quality and integrity of our food is the foundation of our business. That's why we took extra caution to test and retest the chicken. Our customers can have confidence in our food. The allegation that our chicken is only 50% chicken is 100% wrong.

Subway did not respond to Ars’ request for more information about their testing methods and results.

The CBC is standing by its results—mostly. In a report from late Wednesday, the outlet released more of its data, though not the methods or calculations it used for its interpretation. Oddly, the outlet also wrote, “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.”

However, when the CBC first reported the results of its investigation, the outlet’s headline was (and still is): “What's in your chicken sandwich? DNA test shows Subway sandwiches could contain just 50% chicken.” The story also did not include any nuanced description or limitations of the investigation’s findings.

The CBC did not respond to Ars’ request for comments on the testing or how it should be interpreted.

Ultimately, Camire says, when you go to a fast food restaurant, expect that there’s some added ingredients. For large-scale production and standardization, manufacturers use spices and extra proteins to boost flavor. And, she said, keep in mind that they tend to have a lot of salt.

(3/3/2017) This post has been updated and corrected. The article previously stated that the chicken may contain soy protein made using yeast but should have stated that the chicken may contain soy protein with yeast flavoring.