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Is sushi safe to eat?
In the UK, sushi restaurants started opening around the capital from the mid-1990s. London’s diverse culinary scene was crucial for the growth in sushi’s popularity across the UK as the capital has typically been the first city to embrace new foods, restaurants and cuisines before spreading out across cities around the country.
Fast forward some 25 years and the latest figures from Seafish, the public body supporting the seafood industry in the UK, show that the chilled sushi retail market is now worth £68 million in the UK.
Sushi is the fourth most popular Asian food in the UK according to a survey, with restaurants remaining the most popular place for the consumption of sushi. However, ready-made sushi bought from supermarkets, sushi meal kits and, increasingly, food delivery services, has seen home consumption of sushi take off in the last few years.
What is sushi?
Sushi is a Japanese dish featuring specially prepared rice and usually some type of fish or seafood, often raw, but sometimes cooked. Sushi originated in Southeast Asia and travelled to Japan over 2000 years ago; initially sushi arose out of a way of preserving food. Fish was placed in rice and allowed to ferment, which allowed people to keep the fish edible for some time.
The rice was thrown away and the fish was eaten when needed or wanted. Centuries later, people began to use raw fish instead of cured fish, and consumed the rice too, which is the most common form of sushi today. The word sushi refers to the sour flavour of the vinegared rice. The Japanese word “su” means “vinegar”, and “shi” is from “meshi”, the Japanese word for “rice”, hence sushi is vinegared rice.
Regardless of the toppings or fillings, sushi always includes rice. Sushi rice is a medium-grained white rice with somewhat rounded grains, which makes it noticeably different from the skinnier, long-grained rice that we are used to in the West. The usual variety of rice used for sushi is Japonica, which is starchy.
The rice is prepared with vinegar and other seasonings such as salt and sugar. Because sushi is the rice and not, as many believe, the fish, it is also possible to substitute the fish for a vegetable such as cucumber, avocado slices, peppers, or courgette to create delicious vegetarian sushi.
But what are the different kinds of sushi? There are three main types of sushi. They are nigiri sushi, maki sushi, and oshi sushi.
- Nigiri sushi – A topping of fish served on top of sushi rice. For nigiri sushi, a slice of raw or cooked fish or shellfish is pressed onto a mound of vinegared rice, with a little wasabi in between. In some cases, nigiri sushi uses a small strip of toasted seaweed called nori to bind the whole mixture together. Nigiri sushi is commonly called two-kinds-sushi because it involves two ingredients: sushi rice and a single topping. The topping is also known as neta, and usually takes the form of a type of seafood such as tuna, eel, haddock, shad, snapper, octopus, or shrimp. Depending on the type of fish, it may be served raw in thin slices, grilled, or batter fried.
- Maki sushi – Fish circled by rice and surrounded by seaweed. For maki sushi, layers of raw or cooked fish or shellfish, vegetables and vinegared rice are placed on a sheet of dried sea kelp and rolled into a cylinder then cut into pieces. The word maki means “roll”. There are a variety of types, including uramaki which is complex and requires the attention of a skilled chef. Others such as temaki are very easy to make, and frequently eaten at home and at social gatherings. Uramaki is an inside out roll, meaning that the sushi rice is on the outside. Nori is covered with sushi rice and then flipped over. The fillings are added and the maki is rolled up. The roll may then be dipped in, or topped with, garnishes like sesame seeds or fish roe. This type of maki is more common outside of Japan, and includes the well-known California and Philadelphia rolls. Emaki is a sushi roll formed in the shape of a cone. Nori sheets are cut in half so that a small pile of sushi rice and fillings can be made on one corner. Then the nori is tightly rolled in a conical shape which can easily be held by hand while it is dipped into an assortment of sauces, including soy sauce and wasabi, and eaten. These hand rolls are a more casual type of sushi, and also have a fun visual appearance, with ingredients overflowing from the cone like a cornucopia.
- Oshi sushi – Is a type of sushi from Osaka. It means “pressed sushi” or is also called “box sushi”. This is one of the oldest forms of sushi and stems from the ancient method of preserving fish by packing it tightly in boxes with fermented rice. Today, pressed sushi made with sushi rice and mackerel is one of the most popular forms of takeout food bought at airports by Japanese travellers. A wooden mould, called an oshibako, is used to make this form of sushi.
One of the most common misconceptions about sushi is that sashimi is a type of sushi; it isn’t, although sushi and sashimi do have similarities. The word sashimi, which translates roughly to “pierced meat” or “pierced body”, refers to slices of raw fish, seasoned with soy sauce, wasabi, miso, or ginger; however, there is no rice involved in sashimi, so it is not sushi.
Most sashimi is served raw, although some items are briefly cooked, either braised, seared or boiled, mainly for flavour and texture, but also to avoid food poisoning.
Is sushi safe to eat?
Some people worry about whether sushi is safe to eat, because raw foods typically carry a higher risk of foodborne illness. Sushi, and seafood in general, may be one of the best sources of nutrition available to us as it is packed with protein, dense with nutrients, and often low in fat.
Sushi is an excellent source of lean protein and contains very little heart-clogging saturated fat, unlike meat from terrestrial animals, and what fat is available is mostly in the form of omega-3 fatty acids. The seaweed wrap used in maki-sushi rolls, called nori, is rich with essential vitamins and minerals.
- Vitamin D.
- Vitamin B2 (riboflavin).
- Vitamin B1.
- Vitamin C.
- Vitamin A.
- Vitamin E.
Other sushi ingredients such as wasabi and ginger both have antibacterial qualities, and ginger is widely regarded as aiding digestion, improving circulation and can also help protect against respiratory viruses.
Sushi-grade fish means that it is deemed safe to eat raw because of the way it is treated from the catch, throughout transportation and storage. The bacteria level is lower than regular fish, which makes it safe to eat uncooked.
Sushi safety concerns
As with any raw food there is some degree of risk of foodborne pathogens, but with seafood another safety concern is contaminants. Essentially, the higher up the food chain a fish is, the more contaminants concentrate.
Contaminants such as mercury can be present in fish, especially the larger predatory fish such as tuna and swordfish which are used in both sushi and sashimi. All fish contain some level of mercury, but most of the fish that is used in sushi rolls and sashimi are large fish, such as tuna, yellowtail, bluefin, sea bass and lobster, and they have been found to have the highest amounts of mercury.
Mercury poisoning can lead to:
- Memory problems.
- Muscle weakness.
- Numbness and tingling.
- Tremors and irritability.
Another contaminant is the trillions of barely visible pieces of plastic that are floating in the world’s oceans, from surface waters to the deep seas. These particles, known as microplastics, typically form when larger plastic objects such as shopping bags and food containers break down.
Marine fish, including species consumed by humans, can ingest synthetic particles of all sizes. Fish such as sharks, grouper and tuna that hunt other fish or marine organisms as food, are more likely to ingest plastic. Consequently, species higher up the food chain are at greater risk including humans.
Aside from contaminants, raw seafood can also be the route for various pathogens: viral, bacterial, as well as larger parasitic creatures. Listeria, salmonella and tapeworms are just a few risks that could make you consider whether sushi is safe to eat or not.
One common disease associated with sushi consumption is anisakiasis. It is caused by eating fish infected with a parasitic worm which attaches to your oesophagus, stomach, or intestines and can cause food poisoning. Anisakiasis cannot be transmitted human to human. The symptoms typically develop within 5 days after the ingestion of infected food.
The signs and symptoms of anisakiasis are:
- Abdominal pain.
- Abdominal distention.
- Blood and mucus in stool.
- Mild fever.
Allergic reactions with rash and itching, and infrequently anaphylaxis, can also occur.
Listeria is another common concern with sushi and smoked seafood. Listeria monocytogenes causes listeriosis in humans, mainly through consumption of ready-to-eat foods such as sushi.
Raw, smoked or cured fish products and seafood such as sushi, sashimi, oysters, and cold or hot smoked fish, for example smoked salmon and cured fish, are frequently contaminated with listeria. In most people, listeriosis usually has no symptoms or only causes mild symptoms for a few days.
- A high temperature of 38ºC or above.
- Aches and pains.
- Feeling or being sick.
However, if you have a high fever, severe headache, stiff neck, confusion or sensitivity to light, seek medical help. These signs and symptoms can indicate bacterial meningitis, a life-threatening complication of a listeria infection.
Salmonella is another foodborne illness often found in raw fish and meat that is not properly prepared. Salmonella infection causes symptoms of diarrhoea, fever and stomach cramps, often beginning within one to three days of eating the contaminated food.
In older people or those with weakened immune systems, however, it can become more serious, causing dehydration or entering the bloodstream. In some cases, the diarrhoea associated with salmonella infection can be so dehydrating as to require prompt medical treatment. Life-threatening complications also may develop if the infection spreads beyond your intestines.
Pathogenic bacteria such as Bacillus cereus is commonly found in rice. It is recognised that mixing sushi rice with vinegar and salt seasoning will reduce the acidity of the mix, which in turn will help prevent the growth of bacteria and the formation of their toxins, for example Bacillus cereus. This will enable it to be left out of temperature control for long periods, such as when making sushi.
What are the risks of eating sushi?
Above we have looked at some of the food safety concerns associated with eating sushi. However, properly trained sushi chefs, known as Itamae, know how to buy, examine, store and handle fish and rice to minimise the risk of illness and parasites. These knowledgeable Itamae will easily detect anisakis larvae, which is quite visible in raw fish.
Food safety regulations in the UK require shops and restaurants to freeze raw fish at -20ºC for at least 24 hours, or at -35ºC for at least 15 hours, before they make sushi. Freezing raw fish in this way kills the parasites and makes it safe to eat.
Sushi sold in supermarkets has been ready-made in a factory where any raw fish is frozen beforehand. The same goes for any restaurant that buys in ready-made sushi.
There is, however, another health risk associated with eating sushi. Many types of sushi contain high levels of sodium.
The popular sushi topping, soy sauce, is also high in sodium. Most people already have too much sodium in their diets, and high sodium levels can lead to problems that include congestive heart failure and kidney disease.
Sushi should be eaten the day it is prepared. It can be kept for up to two hours but no longer, at room temperature, but if it is to be consumed more than two hours after preparation, you must refrigerate your sushi or keep it in a cool place. After refrigeration, you need to take it out about 30 minutes to an hour before consumption so that the rice isn’t too cold.
If you are feeling adventurous and make your own sushi at home, freeze the fish for at least 24 hours before using it, or if you want to be really careful, stick to vegetarian sushi.
Is sushi safe to eat while pregnant?
Due to the potential for contaminants such as mercury, as well as pathogens, pregnant women are told to avoid the larger, predatory fish, and any raw meat; something that those with weakened immune systems are also told to avoid as well. The NHS confirms that in the UK it is safe to eat sushi and other dishes made with raw or other lightly cooked fish when you are pregnant, as long as the raw fish has been frozen first; shellfish sushi, however, is not safe unless it is fully cooked.
Sushi that uses cooked fish and shellfish, such as crab, cooked prawns and cooked eel, is fine to eat while you are pregnant. Vegetarian sushi, which uses ingredients such as cooked egg, cucumber or avocado, is also safe for you to eat when you are pregnant.
Can anyone eat sushi?
There are certain people for whom sushi is not safe. People with compromised immune systems should not eat it, because if there are lingering parasites or bacteria, they could easily overwhelm the body while it is weak. It is also recommended that the elderly and small children should also avoid eating sushi.
Sushi is as safe as any other food as long as the proper handling conditions are met. In fact, there are actually some excellent health benefits to eating sushi. Traditional sushi is rich in omega-3 fish oils which we all know are excellent for our health.
These fish oils are essential fats that cannot be produced by the body itself, so it is recommended we add it into our diet. Omega-3 fish oils are excellent at reducing high cholesterol levels, lowering your blood pressure and reducing your risk of heart disease, among other benefits.
As well as being rich in omega-3, sushi is full to the brim with other essential minerals that keep our immune system functioning. This includes minerals such as zinc, magnesium, calcium and iron. In our normal diets, it is sometimes difficult to get a decent helping of these minerals which is why many people take supplements.
Possibly the most enticing benefit is that, eating sushi can actually work wonders in reducing food cravings. The fish used to make sushi is an excellent source of protein that aids in balancing blood sugar levels and keeps your energy levels stable. By doing so, it helps boost your metabolism which can help you to burn calories faster and make you feel fuller for longer.
Protein can also aid hair growth, strengthen your nails and speed up muscle repair, which is why many athletes and body builders will regularly incorporate sushi into their diets.