#1 Sushi Health Risk—Parasites, with 7 Tips to Protect Yourself

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Parasites in Sushi

Might that plate of sushi be contaminated with parasites?

An informal poll by Gastroenterology & Endoscopy News showed that most doctors who specialize in digestive diseases (at a rate of three to two) do not eat sushi because of the concerns of foodborne illness.

Do these doctors know something you don’t? What are the risks when eating sushi, and how can you increase your odds of avoiding the contaminated kind?

Sushi Not as Healthy as You Think

Sushi has become more popular in the U.S. over the last decade. Not only do many find it tasty, but most of us also have the idea that it’s good for us. It’s raw, and it’s fish—what’s not to like?

Some health experts, however, say we’ve got it all wrong. First, lets talk calories. A single California roll containing crabstick and avocado can easily contain 400 calories and two grams of salt. A basic salmon avocado roll will have around 300 calories, but Americanized versions that add cream cheese or mayonnaise will contain even more. If you add in the soy sauce, you’re getting a good serving of sodium as well. Depending on what you eat the rest of the time, this could be bad for your heart.

It’s good to be aware of the potential calorie-load with sushi, but when it comes to our health, other potential dangers can be more significant.

Health Risk #1: Parasites

The biggest health risks of sushi are parasites, heavy metals, and bacteria. We’ll talk about the other two dangers in future posts. Today, we’ll focus on parasites.

The general rule is that fish served raw in this country has been flash-frozen before you eat it. The FDA requires that all fish (with the exception of tuna) destined to be served raw in the U.S. be frozen at a minimum of minus four degrees Fahrenheit for seven days or minus thirty-one degrees for fifteen hours. Either process kills parasites inside of a fish, and also keeps it fresh.

(Note: Home freezers can’t freeze fast enough to cause the same effect, so don’t expect that you can kill parasites by freezing fresh fish at home. Parasites can survive the process, and such freezing can also damage the fish flesh.)

The FDA’s requirement means that most sushi in the U.S. is likely to be free of parasites—but there are some exceptions. Some diners, for instance, may be sensitive to even dead parasites, and can suffer from stomach pain and vomiting if they eat them in sushi. In other cases, the fish may not have been frozen and may be contaminated with parasites. This may occur in some specialty shops that pride themselves on serving “fresh,” raw fish. (It’s always good to ask.)

One of the most well known diseases that comes from eating raw fish is called “anisakiasis.” A rare disease, it has occurred in the U.S. because of the increasing popularity of sushi. The symptoms are similar to other types of food poisoning, and come from eating sushi or sashimi infected with the larvae of a parasitic worm called “Anisakidae.” Chefs usually spot the worm, but not always. Most of the time any such worms will die within 24 hours of being eaten, but some can last longer, causing havoc in the digestive system before they finally succumb. They can also cause allergic reactions while alive in the stomach or intestines.

Since this condition is rare in the U.S., it is often misdiagnosed as appendicitis or an ulcer, so it’s always important, if you’re suffering from stomach pain, to tell your doctor that you recently ate sushi.

“Diphyllobothriasis” is an intestinal infection caused by the fish tapeworm D. latum, which is usually found in trout, salmon, pike, and sea bass. Infection can cause reduced blood levels of vitamin B12 and anemia. Again, this is only possible when eating raw fish that has not been frozen. There are other types of parasites that may contaminate raw fish. So far, most of these have been reported in Japan, Thailand, and other countries, but not in the U.S.

How to Protect Yourself

Following are some tips to help you increase your odds of enjoying your sushi while decreasing your risk of a stomachache caused by parasites:

  1. Saltwater fish: Saltwater fish are less likely to be infected than fresh-water fish. Choose albacore, Atlantic cod, rockfish, eel, flounder, grouper, halibut, Pacific bluefin tuna, and swordfish to raise your odds of avoiding parasites. Freshwater fish like catfish, trout, and sturgeon have a slightly higher risk of infection.
  2. Wasabi: Use your wasabi—it naturally kills parasites.
  3. What ocean? Choose fish from the Atlantic Ocean over those from the Pacific Ocean—the Pacific has a higher population and can spread more parasites.
  4. Farmed may be better: If you’re going for raw fish, choose farmed over wild-caught. Farmed fish are raised in controlled environments and rarely have parasites. (Check the source on farmed salmon—see our post for more. Some organic farmed salmon is safe, but others are full of contaminants.)
  5. Choose tuna: They are so rarely infected by parasites that the FDA doesn’t even require them to be frozen to kill parasites, though most manufacturers freeze them anyway. Tuna are fast-moving fish and are rarely in areas where parasites spread. Note, however, that they may be higher in mercury and other metals than other types of fish. Ahi and bigeye Tuna are usually the highest in mercury. Canned, chunk light is one of the lowest in mercury of all tuna types.
  6. Ask for “sashimi grade” fish: These fish go through all of the FDA measures to guarantee safety. They are inspected and found to be at least very low in parasites, and then are frozen to the point that parasites cannot survive.
  7. Ask for young fish: They have been around for less time than older fish, and will be less likely to have contracted parasites.

How do you choose the safest sushi? Please share your tips.

* * *

“CDC research shows outbreaks linked to imported foods increasing,” CDC Press Release, March 14, 2012, http://www.cdc.gov/media/releases/2012/p0314_foodborne.html.

“2 Investigators: Is Your Sushi Safe?” CBS News, October 27, 2011, http://chicago.cbslocal.com/2011/10/27/2-investigators-is-your-sushi-safe/.

Christina Frangou, “An Informal Poll of Gastroenterologists on Sushi: Do Those Who Treat Also Eat?” Gastroenterology & Endoscopy News, April 2006, http://www.gastroendonews.com/ViewArticle.aspx?d_id=187&a_id=6700.

Dr. Danny Penman, “Sushi—the raw truth,” Daily Mail, April 4, 2006, http://www.dailymail.co.uk/health/article-381958/Sushi–raw-truth.html.

Blair Mathis, “Parasites and Sushi: Information About Consuming Raw Fish for Travelers to Japan,” Yahoo! Voices, July 1, 2008, http://voices.yahoo.com/parasites-sushi-information-consuming-raw-1561167.html.

Yukifumi Nawa, “Sushi Delights and Parasites: The Risk of Fishborne and Foodborne Parasitic Zoonoses in Asia,” Clin Infect Dis. 2005; 41(9): 1297-1303, http://cid.oxfordjournals.org/content/41/9/1297.full.

Ross Christensen, “How safe is your sushi? Part Two: Parasites!” Eatsushi, http://www.eatsushi.com/article.asp?X=628.

Colleen M. Story

Colleen M. Story



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