Permaculturist Health

[Lawrence London <lfljvenaura@gmail.com>]

https://www.nhs.uk/live-well/eat-well/fish-and-shellfish-nutrition/#

• Food and diet
• Recipes and tips
• Digestive health

Page contents

1. Types of fish
2. Oily fish and omega-3 fatty acids
3. How much fish should we eat?
4. Taking fish liver oil supplements
5. Eating sustainable fish and shellfish
6. Fish and shellfish safety

Fish and shellfish

A healthy, balanced diet should include at least 2 portions of fish a week, including 1 of oily fish.

That's because fish and shellfish are good sources of many vitamins and minerals. Oily fish – such as salmon and sardines – is also particularly high in long-chain omega-3 fatty acids, which can help to keep your heart healthy.

Most of us should have more fish in our diet, including more oily fish.

There is different advice for women who are pregnant or breastfeeding, and children and babies.

Fish that is steamed, baked or grilled is a healthier choice than fried fish. Frying can increase the fat content of fish and shellfish, especially if they’re cooked in batter.

To ensure there are enough fish to eat now and in the future, we should try to eat a wide variety of fish and to buy fish from sustainable sources.

Types of fish

Different types of fish and shellfish provide different nutrients.

Oily fish

Oily fish include:

• herring (bloater, kipper and hilsa are types of herring)
• pilchards
• salmon
• sardines
• sprats
• trout
• mackerel

Fresh and canned tuna do not count as oily fish.

Oily fish are:

• high in long-chain omega-3 fatty acids, which may help to prevent heart disease
• a good source of vitamin D

Some oily fish contain bones that you can eat. These include whitebait, canned sardines, pilchards and tinned salmon (but not fresh salmon). These fish can help keep our bones strong because they are sources of calcium and phosphorus.

White fish

Cod, haddock, plaice, pollock, coley, dab, flounder, red mullet, gurnard and tilapia are all examples of white fish. 

White fish are:

• low in fat, making them one of the healthier, low-fat alternatives to red or processed meat, which tends to be higher in fat, especially saturated fat
• some species can be a source of omega-3 fatty acids, e.g. sea bass, sea bream, turbot, halibut, but at lower levels than oily fish

Shellfish

Shellfish includes prawns, mussels, scallops, squid and langoustine. 

Shellfish are:

• low in fat
• a source of selenium, zinc, iodine and copper

Some types of shellfish, such as mussels, oysters, squid and crab, are also good sources of long-chain omega-3 fatty acids, but they do not contain as much as oily fish.

Oily fish and omega-3 fatty acids

Oily fish contains long-chain omega-3 fatty acids. Long-chain omega-3 can help to prevent heart disease. It is also important for women who are pregnant or breastfeeding, because it can help a baby's nervous system to develop.

Oily fish are the richest source of long-chain omega-3. Some white fish and shellfish also contain long-chain omega-3, but not as much as oily fish.

The main shellfish sources of long-chain omega-3 are:

• mussels
• oysters
• squid
• crab

How much fish should we eat?

A healthy, balanced diet should include at least 2 portions of fish a week, including 1 of oily fish. Most of us aren't eating this much. A portion is around 140g (4.9oz).

However, for certain types of fish, there are recommendations about the maximum amount you should eat.

How much oily fish should I eat?

We should eat at least 1 portion (around 140g when cooked) of oily fish a week.

Oily fish can contain low levels of pollutants that can build up in the body. For this reason, there are maximum recommendations for the number of portions some groups should be eating each week.

The following people should eat no more than 2 portions of oily fish a week:

• girls
• women who are planning a pregnancy or may have a child one day
• pregnant and breastfeeding women

This is because pollutants found in oily fish may build up in the body and affect the future development of a baby in the womb.

How much white fish should I eat?

You can safely eat as many portions of white fish per week as you like, except for the following, which may contain similar levels of certain pollutants as oily fish:

• sea bream
• sea bass
• turbot
• halibut
• rock salmon (also known as dogfish, flake, huss, rigg or rock eel)

Anyone who regularly eats a lot of fish should avoid eating these 5 fish, and brown meat from crabs, too often.

Even though shark and marlin are white fish, there is separate advice about how much of them you should eat:

• children, pregnant women and women who are trying to get pregnant should not eat shark, swordfish or marlin, because they contain more mercury than other fish
• other adults should have no more than 1 portion of shark, swordfish or marlin a week

Many shark and marlin species are endangered, so we should avoid eating these fish to help stop these species becoming extinct. See the sustainable fish and shellfish section below for more information. 

How much shellfish should I eat?

Although it is recommended that regular fish-eaters should avoid eating brown crab meat too often, there is no need to limit the amount of white crab meat that you eat. There are no maximum recommended amounts for other types of shellfish.

Eating fish while trying to get pregnant, and during pregnancy and breastfeeding

Eating fish is good for your health and the development of your baby. However, pregnant and breastfeeding women should avoid some types of fish and limit the amount they eat of some others. This is because of the levels of mercury and pollutants that some fish can contain.

When pregnant, you can reduce your risk of food poisoning by avoiding raw shellfish and making sure that any shellfish you eat is cooked thoroughly.

Below is advice from the Scientific Advisory Committee on Nutrition (SACN) and the Committee on Toxicity about eating fish when trying to get pregnant, or when pregnant or breastfeeding:

Shark, swordfish and marlin: do not eat these if you are pregnant or trying to get pregnant. All other adults, including breastfeeding women, should eat no more than 1 portion per week. This is because these fish can contain more mercury than other types of fish, and can damage a developing baby's nervous system.

Oily fish: all girls and women who haven’t been throught the menopause yet, including those trying for a baby, or who are pregnant or breastfeeding, should have no more than 2 portions of oily fish a week. A portion is around 140g.

Tuna: if you are trying for a baby or are pregnant, you should have no more than 4 cans of tuna a week or no more than 2 tuna steaks a week. This is because tuna contains higher levels of mercury than other fish. If you are breastfeeding, there is no limit on how much tuna you can eat.

These figures are based on a medium-sized can of tuna with a drained weight of around 140g per can and a 140g cooked steak.

Remember, tuna doesn't count as oily fish. So if you've had a portion of tuna during the week, you can still have up to 2 portions (women) or 4 portions (men) of oily fish. 

Unless your GP advises otherwise, avoid taking fish liver oil supplements when you're pregnant or trying for a baby. These are high in vitamin A (retinol), which can be harmful to your unborn baby. Pregnant women are advised to avoid taking supplements that contain vitamin A.

Learn more about having a healthy diet in pregnancy and foods to avoid in pregnancy.

Should children and babies over 6 months eat fish?

Children under the age of 16 should avoid eating any shark, swordfish or marlin. This is because the levels of mercury in these fish can affect a child's nervous system.

Avoid giving raw shellfish to babies and children to reduce their risk of getting food poisoning.

Learn more about healthy eating for the under-5s in Your baby's first solid foods.

You can give boys up to 4 portions of oily fish a week, but it is best to give girls no more than 2 portions a week. This is because the low levels of pollutants that oily fish contain can build up in the body and may harm an unborn baby during a future pregnancy.

Taking fish liver oil supplements

If you take fish liver oil supplements, remember that these are high in vitamin A. This is because fish store vitamin A in their livers. Having too much vitamin A over many years could be harmful.

The Scientific Advisory Committee on Nutrition advises that if you take supplements containing vitamin A, you should not have more than 1.5mg a day from your food and supplements combined. Pregnant women are advised to avoid taking supplements containing vitamin A, including fish liver oil supplements, as too much vitamin A can be harmful to an unborn baby. Learn more about vitamin A.

Eating sustainable fish and shellfish

When fish or shellfish are caught or produced in a way that allows stocks to replenish and that does not cause unnecessary damage to marine animals and plants, those fish or shellfish are called "sustainable".

To ensure there are enough fish and shellfish to eat, choose from as wide a range of these foods as possible. If we eat only a few kinds of fish, then numbers of these fish can fall very low due to overfishing of these stocks.

Overfishing endangers the future supply of the fish and can also cause damage to the environment from which the fish is caught.

Fish and shellfish safety

Eating fish or shellfish that is not fresh or that has not been stored and prepared hygienically can cause food poisoning. In this section, you can find tips on how to store and prepare fish and shellfish.

Shellfish such as mussels, clams and oysters that are raw or not thoroughly cooked can contain harmful viruses and bacteria that can cause food poisoning. Thorough cooking usually kills any bacteria or viruses.

Most of the shellfish we eat is cooked first, but oysters are often served raw. 

Raw shellfish, particularly oysters, can contain low levels of certain viruses, such as norovirus. If you are serving oysters raw, be especially careful when buying and storing them.

Shellfish can also contain toxins.

Depending on the type of toxin present, the symptoms from eating contaminated shellfish may include: 

• nausea
• vomiting
• diarrhoea
• headaches
• numbness
• breathing difficulties
• memory loss
• disorientation
• abdominal pain 

These toxins do not break down during cooking.

The Food Standards Agency (FSA) advises that older people, pregnant women, very young children and people who are unwell should avoid eating raw or lightly cooked shellfish to reduce their risk of getting food poisoning.

Catching fish and shellfish

Is fishing your passion? Like the thought of eating your own fresh catch? First read this guidance on avoiding parasites if you want to eat your own catch of Atlantic salmon and sea trout.

If you want to take shellfish from any public waters, it's important that you check local notices or with your local authority that the area isn't closed to fishing. If it is closed, it may be for public health reasons, such as high toxin or bacterial or chemical contamination, in which case it would be dangerous to eat shellfish from that area.

Buying fish and shellfish

When choosing fish and shellfish, remember:

• buy fish and shellfish from reputable sources
• choose fresh fish or shellfish that is refrigerated or kept on ice
• do not buy cooked or ready-to-eat fish or shellfish that is touching raw fish or shellfish
• when shopping, pick up fish and shellfish last and take it straight home. Fish and shellfish go off very quickly once out of the fridge
• when buying or cooking live shellfish such as mussels, make sure that the outer shell closes when you tap it. Live shellfish will "clam up" when their shells are tapped

• where possible, buy fish and shellfish from sustainable sources

  Storing fish and shellfish

Follow these hygiene tips when storing fish:

• put fish and shellfish in the fridge or freezer as soon as you get home
• make sure that all fish and shellfish are in covered containers, but don't put mussels, oysters, clams or any other live shellfish into airtight containers, because they need to breathe
• do not store fish or shellfish in water
• discard mussels, oysters, clams or any other live shellfish if their shells crack or break, or if the shells are open and do not close when you tap them. Live shellfish will "clam up" if their shells are tapped

Preparing fish and shellfish

Follow these hygiene tips when preparing fish:

• wash your hands thoroughly before and after handling fish or shellfish
• do not allow raw fish or shellfish or fluid from live shellfish to come into contact with cooked or ready-to-eat food
• use separate plates and utensils for preparing raw fish and shellfish and other food
• thaw frozen fish or shellfish in the fridge overnight. If you need to thaw it more quickly, you could use a microwave. Use the "defrost" setting and stop when the fish is icy, but flexible
• if you're marinating seafood, put it in the fridge and throw the marinade away after removing the raw fish or shellfish. If you want to use the marinade as a dip or sauce, set some aside before it touches the raw fish
• do not eat clams or mussels that do not open when cooked. It is likely that the clam or mussel has died, and that it is not safe to eat

Fish and shellfish allergy

Allergies to fish or shellfish are quite common and can cause severe reactions.

People who are allergic to one type of fish often react to other types. Similarly, people who are allergic to one type of shellfish, such as prawns, crabs, mussels or scallops, often react to other types.

Cooking fish or shellfish doesn't make someone with a fish or shellfish allergy less likely to have a bad reaction.

Learn more about food allergies.

Page last reviewed: 04/12/2018
Next review due: 04/12/2021