What's in the tuna salad? Fact-checking the Subway fish sandwich scandal

Greyish brown globs of tuna — mixed with a healthy dollop of mayonnaise — may not win any beauty contests in the world of sandwiches. Nevertheless, this all-American underdog has stood the test of time as a standard lunchtime offering across the country.

But an ongoing lawsuit aimed at the fast-food sandwich king — Subway — suggests we should be a little choosier about who we get our tuna fish from. The contents of these sandwiches may not be really tuna at all.

That’s what the lawsuit alleges. In the pursuit of the truth, the New York Times sent Subway’s tuna to a commercial food testing lab. The results? “No amplifiable” tuna DNA.

But the story remains as murky as the mayo holding the tuna fish together. Karen James, a molecular ecologist at the University of Maine, tells Inverse the lack of tuna DNA isn’t necessarily something tuna fish-lovers should stress about. It may, however, point toward even more worrying issues, including unsustainable fishing practices and seafood mislabeling.

James wrote a popular thread on Twitter expanding on the shortcomings of this analysis after she read about it in the Times.

“I was really excited when I started reading it [but] I had this kind of growing sense of ‘oh no we're not going to learn anything about the lab work’,” James says. “That's what prompted my thread”

Subway’s tuna lawsuit

In case you missed the drama, here’s a rundown of the now-infamous lawsuit against Subway’s tuna sandwich as initially reported by the East Bay Times:

• In January 2021, two Subway customers from Alameda County in California sued the sandwich shop claiming that the tuna fish in their sandwich was “anything but tuna” and “various-concoctions-that-do-not-constitute-tuna.”
• The plaintiffs in the case, Karen Dhanowa and Nilima Amin, claimed the suspicious sandwich was an attempt to “capitalize on the premium price consumers are willing to pay for tuna.” Tuna, however, is already known as a very affordable fish.
• The pair also noted “emotion distress” at the hands of the sandwich.
• Subway has denied these allegations, stating:

“Subway delivers 100% cooked tuna to its restaurants, which is mixed with mayonnaise and used in freshly made sandwiches, wraps and salads that are served to and enjoyed by our guests. The taste and quality of our tuna make it one of Subway’s most popular products and these baseless accusations threaten to damage our franchisees, small business owners who work tirelessly to uphold the high standards that Subway sets for all of its products, including its tuna.”

Since January, the plaintiffs have walked back their initial claims to instead argue that Subway’s tuna is not sustainably caught as the restaurant claims. But the damage had been done, and it became a media sensation.

Is there really tuna in Subway sandwiches?

When the Times dug deeper into this scandal (by mailing frozen samples of Subway’s tuna to an independent lab for testing) they announced in June that they found that the lab results couldn’t confirm whether or not there was any tuna DNA in the samples.

This sounds scary, but James said there’s a lot of different reasons why the lab might’ve had these results — and it’s not just because the sandwiches are mystery meat.

“When an organism dies or there's just DNA in the environment it is getting damaged,” James explains. “It can be damaged by environmental factors. It can be physically broken or fragmented. And if it's inside say a piece of fish, as the cells start to slowly degrade — hopefully very slowly in the case of food — the cells become compromised.”

Any DNA damage can make it more difficult for scientists to successfully test the sample, she explains.

“You know, there could very well have been tuna.”

To test the tuna samples for DNA James says the lab (whose name was undisclosed by the Times) would’ve done a polymerase chain reaction (PCR) test to:

• Isolate the DNA
• Amplify (aka, create more copies) of it
• Compare that result with a benchmark DNA sample for the specimen

In this case, the sample would be compared against an authentic tuna DNA sequence. This is essentially the same process your Covid-19 tests go through — minus the fish.

This process can be challenging at the best of times, says James, but would be especially challenging for a sample like the Times.’ This is because it had been through so many processing steps already.

To be sure they were getting an accurate read on the fish, assuming its DNA wasn’t too damaged, the lab would’ve needed a number of control samples as well such as separate tuna samples also covered in mayonnaise.

“I'm not saying the testing company did not do these things,” James says. “[But] we weren't told any of this in the New York Times article. So in the absence of that information you just have to conclude that we don't know. You know, there could very well have been tuna.”

While James says she hasn’t eaten a Subway sandwich in years, she’s willing to bet her lunch that Subway tuna fish is the real deal and not a mysterious concoction.

“I would eat a Subway tuna sub,” James says.

Is mislabeled seafood dangerous?

While there’s not enough evidence either way from this analysis, James says that, overall, mislabeling seafood is a pervasive problem that poses a potential health risk (for example, igniting an allergy). For example, an infamous 2017 study that analyzed the DNA for fish ordered across 26 Los Angeles restaurants found 47 percent of the sushi was mislabeled — a finding the researchers explained introduced unexpected health risks to children, pregnant women, and people who need to avoid high-mercury fish.

Mislabeling also serves as a loophole for ecologically damaging fishing practices.

“Ideally, you'd be able to say not only if there is fish DNA but it's tuna, and not only is it tuna but it’s this species of tuna,” explains James.

“And that actually gets the question of whether it's sustainably caught... You can't really do that with a lab test — you can't test for that,” she says. “If it were a certain species of tuna it might give you kind of an insight into whether it would have been possible for it to be sustainably caught.”

When it comes to fishing practices, James says it's possible that a product (e.g. canned tuna) could be marketed as a more ethically harvested species but in fact be filled with a cheaper, less sustainably caught alternative species of tuna. For example, bluefin tuna is heavily overfished while skipjack is generally more resilient.

Swapping one tuna species for another probably wouldn’t make a consumer sick, but it’s a practice that could do irrevocable damage to the marine environment and ecosystem, such as driving species from their natural habitats. And these are environmental changes that will be felt all the way up the food chain to our lunch tables.

Subway claims it only sells skipjack and yellowfin tuna “sourced from fisheries with non-threatened stock levels.” The question is: Do you believe it?

CHECK, PLEASE is an Inverse series that uses biology, chemistry, and physics to debunk the biggest food myths and assumptions.

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