Humans have been eating raw fish in many forms for a very long time. There are raw seafood options in every cuisine I can think of, from the ceviche of Spanish and South American cuisine to the carpaccio of Italy to Hawaiian poke bowls to all of the other dishes you can find across the world.
According to the latest headlines, raw fish comes with some serious downsides. Scientists have apparently found parasites in 96% of sushi-grade tuna in a new study looking at parasitic infections in ocean-caught fish. For anyone who enjoys a spicy tuna roll, it’s a fairly worrisome finding. No one wants live worms as seasoning.
This is a rare case where the truth is pretty much what the media is reporting. Yes, most of the raw fish you eat had parasites in it when it was caught, and yes you are probably getting some of them whenever you sit down to a plate of sushi, carpaccio, or ceviche.
Let’s look at the data.
The new study is a very simple piece of research where the authors collected samples from the organs and muscles of 53 ocean bonito tuna and tested them visually and chemically for evidence of parasitic infection. They found that 96% of the fish that they had analyzed had at least one parasite, and most had quite a few.
The most common site of parasitic infection was the intestines, with 66% of the fish having at least one intestinal parasite. The next most common place to find a parasite was the muscles, followed by the stomach and liver. There were far fewer parasites found in the brain, gonads, kidneys, hearts, or spleen.
Humans mostly eat the muscles of tuna. Of the muscle samples tested in this experiment, 58% had evidence of at least one parasite. I think it’s therefore fair to say that this study suggests that you’re probably getting at least some parasites with your ocean-caught tuna sashimi much of the time.
Importantly, the study used “sushi-grade” fish. This is because the term “sushi-grade” has—at least in the US and many other countries*—no real meaning. There is no specific regulation that defines what processes “sushi-grade” fish has to undergo. Some people freeze their “sushi-grade” fish before serving it, but there’s no guarantee that this has happened to any fish that you’re served as sushi.
Also, fun fact: freezing doesn’t actually kill every parasite. Aren’t parasites fun! Photo by Helga Christina on Unsplash
I’m going to be very blunt here: this study has not shown us anything new. Ocean-caught fish have parasites living in them because that’s how nature work, and while freezing can kill some of the parasites it rarely kills them all. There have always been and always will be some parasites living in fish that can only be killed by cooking it.
Take anisakiasis. This is a disease caused by a group of worms in the anisakis genus. These worms live in fish, and can infect humans if the fish hasn’t been cooked. The CDC webpage on anisakiasis has many fun sections, but I think the initial symptoms paragraph is perhaps the most horrifying read:
“Some people experience a tingling sensation during or after eating raw or undercooked fish or squid. This sensation is actually the worm moving in the mouth or throat.”
Anisakiasis is relatively easy to cure, but quite unpleasant if you are unfortunate enough to get it. And we know that it is far more common in places such as Japan where raw fish is eaten more commonly. The only way to get the disease is to ingest the worm, and the main way to do that is eating raw fish. You can reduce the risk of getting anisakiasis by freezing fish appropriately before eating it, but this does not kill all of the larvae and doesn’t eliminate the risk.
On the other hand, the risk is quite small. That paper from Japan implies that around 1 in 10,000 people get anisakiasis from eating raw fish in the country every year. Raw fish is very common in Japanese cuisine, so the risk per meal is likely to be extremely minimal.
That’s the thing about population risks—they don’t mean that much to the individual. I’ve never met someone who has actually had a parasitic infection from eating raw fish, even though we know it happens to thousands of people across the world every year.
If you eat raw, wild-caught fish, you have to accept that this is a risk. There is no perfect method to eliminate parasites from raw fish. As the Japanese paper noted, there are many methods including freezing and careful food handling used in Japan to try and get rid of anisakiasis, and it still happens fairly regularly.
If the idea of eating parasites freaks you out, there are two ways to avoid them:
Only eat raw farmed fish.
Don’t eat raw fish.
Personally, I’ll probably still be eating the occasional tuna poke bowl. Yes, it’s a risk, but for me it’s a reasonably manageable one. If I do get a parasitic infection, well, I’ll have only myself to blame.
*Note: I’ve been told that there are regulations for sushi-grade fish in Japan. However, I could not find these regulations searching in English, so if there are any Japanese readers who could point me to the legislation I’d be very grateful! Also, the EU has a recent regulation requiring all fresh tuna to be frozen appropriately, but this does not seem to impact what you can call the fish (so the term “sushi-grade” is still a bit meaningless).
AloJapan.com