Sushi is an art form: simple, clean, and seemingly nutritious, the contents include nori seaweed, filled with minerals, and dotted with a few veggies and fish protein. Most Westerners who have bought into the trend believed it would be a better option as a prepackaged to-go item, or more healthy dinner selection than a typical sodium-rich Asian dish. The neat, visually pleasing presentation makes it easy to choose a California roll over a deli sandwich, especially when desiring a lighter meal. However, one of the most popular, healthy to-go foods of the several decades has become so normalized that many scarcely remember the general truths and risks associated with eating raw fish.
Raw meat immediately brings salmonella to mind, but there are additional hazards associated with eating raw fish in particular. High levels of contaminants found in delicate slices of sushi or slabs of sashimi can easily dominate any nutritious characteristics therein. Chemicals, heavy metals, and pesticides found in the majority of raw fish (less so in organic or wild-caught fish) are incredibly damaging, and can lead to fertility risks, reduced brain function, and in certain cases, cancer.
According to Professor David Carpenter, an environmental health scientist at the University at Albany, New York, “If you eat a meal of salmon sushi more than twice a year, you will increase your risk of cancer. The contaminants found in fish often overpower its beneficial effects. People think they’re improving their health by eating sushi but they are in fact poisoning themselves.”
In addition to the risks of eating raw seafood, sushi consumers are absorbing high levels of sodium, and an unexpectedly large sum of calories despite its appearance. And although the food is prepared meticulously right before us, it doesn’t mean we would be able to see the chemicals and pollutants which have entered the fish long before being chopped and rolled. Worms are another less attractive concern associated with sushi, as the likelihood of being infected with Anisakis (an ocean-dwelling parasitic worm) or others is present, though rare.
Food-borne Illnesses Connected with Sushi
Anisakis and Diphyllobothrium latum are tapeworms usually living in fish, though they are usually visible, and not usually present in the fish prepared for sushi. As Japanese fishermen have been aware of the presence of parasites in seafood for hundreds of years, sushi generally is made with species of fish who are not typical hosts of such parasites. However, salmon is known as a host for D. latum, although the quality of salmon used for most sushi will not contain a worm.
Those who eat an Anisakis-infected fish may possibly have some uncomfortable symptoms, such as a tingle in the throat and coughing up the worms, or feeling as though the appendix has burst. This is the feeling of the Anisakis escaping through the walls of the intestines into the abdominal cavity. It is possible that the immune system will prompt an intense allergic reaction, jolting the body into rashes and inflammation. Unlike their behavior in the wild, in human hosts, Anisakis will die and be eliminated by the immune system. Yet, if the worm hasn’t been coughed or vomited up, and a person is still sick from a parasitic worm may require medical attention. Worms are usually removed by surgery or endoscopy.
With other varieties of nematodes, or roundworms, occasionally ingested through raw or undercooked fish, an unsuspecting host may feel serious abdominal pain, nausea, and vomiting. These symptoms often occur shortly after ingesting the fish, and have been confused for appendicitis and other stomach diseases. Treatment is similar for all types of parasite, as removal may be necessary for those who have become ill and are still hosting the bug.
In addition to Salmonella, the most widespread foodborne illness associated with raw meat, other bacterial may be present in raw or undercooked seafood, presenting a risk of infection. Vibrio is another species of bacteria dwelling inside the meat of raw fish and shellfish, with two main types occurring in commonly consumed foods. Vibrio parahaemolyticus is usually linked to eating raw seafood, namely oysters, and creates uncomfortable symptoms though it does not typically require antibiotics. An infection may cause abdominal cramps, diarrhea, nausea and vomiting, fever, chills, and headache, though it will disappear on its own.
Vibrio vulnificus is the more rare and potentially dangerous type, which has been discovered in clams, crab, and oysters. People with healthy immune systems are likely to experience stomach pain, diarrhea, and vomiting, while those who have compromised immune systems or liver disease may acquire a fatal illness, septicemia, if the microbe passes into the blood. These bacteria may also cause gastroenteritis in rare cases, yet are more common among those handling the shellfish, caused by infected water entering open wounds.
Sushi has also been known to result in infection from Staphylococcus aureus and Listeria monocytogenes. Bacterial infections can result from poor food handling and unsanitary environments, as well as improper living conditions while the fish was being raised.
Most recently, a widespread salmonella outbreak during early to mid 2012, affecting a reported 425 people in 28 states and the District of Columbia was linked to sushi. One of the most common sushi ingredients, yellowfin tuna, produced by Moon Marine USA was the suspect, leading to 55 hospitalizations, but no deaths.
Two different types of Salmonella infection were discovered in the company’s product comprised of meat scraped from the tuna’s backbone called Nakaochi Scrape, sold wholesale to restaurants and supermarkets. Most cases were caused by Salmonella Bareilly (410), though Salmonella Nchanga was also found in 15 patients.
In 2006, Sushi King, a sushi restaurant in Arkansas was responsible for 123 illnesses and 30 reports of salmonellosis. Following the outbreak, the restaurant agreed to close for sanitation and employee education on safe food handling.
When It’s Safe to Eat Raw Fish
Initially, it was thought that sushi-grade or sashimi-grade fish was acceptable for consumption. That is, until the 2012 outbreak of salmonella, which was technically a sushi-grade yellowfin tuna product. And though parasites are said to be avoided by the types of fish and other meats selected for sushi, it is best to make sure the fish is properly frozen before preparation. Freezing the fish to -4℉ for several hours, according to Japan’s National Health Institute, can kill any parasites and make the food safe for eating. Rules vary in different countries, however, with Canada’s Health Protection Branch suggesting the use of commercial freezers (though no specific temperature), and the U.S. Food and Drug Administration recommending that fish to be eaten raw undergo commercial freezing at -10℉ for 7 days, or 15 hours at -31℉.
You can ask the restaurant or market where you buy your sushi how the fish has been frozen, and at what temperature, to ensure safety against parasites. To avoid bacterial infections, you can do a background check on the particular source of your sushi in order to see if they have had any violations with the local health department in the past, though this may not eliminate the risk entirely. As demonstrated in the 2012 outbreak of salmonella in sushi, and other drastic salmonella outbreaks, the manufacturer can be the source of the infection.
Mercury content in tuna and swordfish is also a concern for many sushi consumers. During periods of high mercury found in these fish, avoid eating sushi, as it may result in illness. And though consuming raw fish is taboo in the United States, sushi and sashimi have been eaten by pregnant women in Japan for ages, as it the risk of food-borne illness is not very high in most cases. Parasites are eliminated by FDA standards for freezing, yet other illnesses may loom in the food handling process. As most sushi restaurants allow you to view the area where they make the dish, it is generally safe.
1. 4 April 2006. Dr. Danny Penman. Daily Mail. Sushi – the raw truth.
2. 2006. Colorado State University. Sushi: Minimizing the Food Risk.
3. 4 August 2008. Carl Zimmer. Discover Magazine. What’s In Your Sushi?
4. 15 April 2009. Ingrid Koo, PhD. About.com. Sushi Scares – Infectious Diseases Associated with Eating Sushi or Raw Fish.
6. University of California Davis. Seafood Network Information Center. Parasites in Marine Fishes.
7. 15 July 2007. Steven Shaw. New York Times. Chicken of the Sea.
Images: BlueSushi.com, Wikimedia commons.