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Food and diet - Fish and shellfish

NHS Choices Feature

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A healthy diet should include at least two portions of fish a week, including one of oily fish.

That is because fish and shellfish are good sources of many vitamins and minerals. Oily fish - such as salmon and fresh tuna - is particularly rich in long-chain omega-3 fatty acids, which may help to keep your heart healthy.

Most of us should have more fish in our diet, including more oily fish. However, there are maximum recommended amounts for oily fish, crab and some types of white fish. There is also additional advice for women who are pregnant or breastfeeding, and children and babies.

For a healthier choice, go for steamed, baked or grilled fish or shellfish, rather than fried. This is because frying makes fish and shellfish much higher in fat, 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 choose fish from sustainable sources.

Types of fish

Different types of fish and shellfish provide different nutrients.

Oily fish

Examples of oily fish are salmon, mackerel, sardines, trout and herring. These are:

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

There are some oily fish with bones that you eat. These include whitebait, canned sardines, pilchards and tinned salmon (but not fresh salmon). These fish can help make our bones stronger because they are good sources of calcium and phosphorus.

White fish

Examples of white fish are cod, haddock, plaice, pollack, coley, dab, flounder, red mullet, gurnard and tilapia.

White fish are:

  • very 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
  • a source of omega-3 fatty acids, but at much lower levels than oily fish

Shellfish

Shellfish includes prawns, mussels and langoustine. They are:

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

Some types, 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

Oily fish contains a special kind of fat, called long-chain omega-3 fatty acids.

Long-chain omega-3 may help 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 and crab.

Which fish are oily fish?

These fish are all oily fish, and so good sources of long-chain omega-3:

  • anchovies
  • carp
  • herring (bloater, kipper and hilsa are types of herring) 
  • jack (also known as scad, horse mackerel and trevally)
  • mackerel
  • pilchards
  • salmon
  • sardines
  • sprats
  • trout
  • tuna (fresh)
  • whitebait

Canned tuna does not count as oily fish. Fresh tuna is an oily fish, but when it is canned the amount of long-chain omega-3 fatty acids is reduced to levels similar to those in other fish.

How much fish?

Most people should be eating more fish, including more oily fish.

A healthy diet should include at least two portions of fish a week, including one of oily fish.

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

How much oily fish?

We should eat at least one portion of oily fish a week. A portion of oily fish is around 140 grams when cooked.

There are recommendations for the maximum number of portions of oily fish we should be eating each week. This is because oily fish can contain low levels of pollutants that can build up in the body.

These recommendations are different for men and women, and there is separate advice on swordfish.

Men and boys:

  • Up to four portions of oily fish a week.

Women and girls:

  • Up to two portions of oily fish a week for women and girls who may become pregnant in the future, or who are pregnant or breastfeeding. This is because pollutants found in oily fish may affect the development of a baby in the womb in the future.
  • Up to four portions of oily fish a week for women who won't become pregnant in the future.

The one exception to the recommendations above is swordfish. Children, pregnant women and women who are trying to become pregnant should not eat swordfish. Other adults should eat no more than one portion of swordfish per week. This is because it can contain more mercury than other fish, and consuming high levels of mercury can cause health problems.

How much white fish?

White fish include cod, haddock, plaice, pollack, coley, dover sole, dab, flounder, red mullet and gurnard.

With the exception of some white fish listed below, you can safely eat as many portions of white fish per week as you like.

Shark and marlin:

  • Children, pregnant women and women who are trying to get pregnant should not eat shark or marlin. This is because they contain more mercury than other fish.
  • Other adults should have no more than one portion of shark or marlin per 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.

Other white fish that may contain similar levels of certain pollutants as oily fish are:

  • 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 five fish, and brown meat from crabs, too often. There is no need to limit the amount of white crab meat that you eat.

Trying to get pregnant, pregnancy and breastfeeding

Eating fish is good for your health and the development of your baby. But pregnant women should avoid some types of fish and limit the amount they eat of some others.

When pregnant, you can reduce your risk of food poisoning by avoiding raw shellfish.

Below is advice from the Scientific Advisory Committee on Nutrition 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 one portion per week. This is because these fish can contain more mercury than other types of fish, and this can damage a developing baby's nervous system.
  • Oily fish: if you are trying for a baby, pregnant or breastfeeding, you should have no more than two portions of oily fish a week. A portion is around 140 grams.
  • Canned tuna: if you are trying for a baby or are pregnant, you should have no more than four cans of tuna 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 canned tuna you can eat.

These figures are based on a medium size can of tuna with a drained weight of around 140g per can. Remember, canned tuna doesn't count as oily fish, so you can eat this as well as your maximum two portions of oily fish.

Due to the higher levels of mercury in tuna, if you're eating canned tuna, don't pick fresh tuna as your 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, which can be harmful to your unborn baby.

Learn more in Have a healthy diet in pregnancy.

Children and babies over six months

Children should avoid eating any shark, swordfish or marlin. This is because the levels of mercury in these fish can affect their nervous systems.

You should also avoid giving raw shellfish to babies and children to reduce their risk of getting food poisoning.

Learn more about healthy eating for the under-fives in Birth to five guide: weaning and beyond.

You can give boys up to four portions of oily fish a week, but it is best to give girls no more than two portions. 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.

Fish liver oil supplements

If you take fish liver oil supplements, remember 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 a total of 1.5mg a day from your food and supplements combined. Learn more in Vitamin A.

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.

To learn more about sustainable fish and shellfish, and what you can do to help, see Defra: the marine environment

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 be a source of viral contamination. A 2011 study funded by the Foods Standards Agency (FSA) found that three-quarters of oysters sampled from harvesting beds within UK waters contained norovirus, although in half of these it was only detected at low levels. Currently, these findings do not provide any greater indication of the risk of becoming ill at the point where oysters are purchased and consumed. If you are serving oysters raw, be especially careful when buying and storing them: see below for more advice.

The 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.  

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.
  • Don't 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 and preparing fish and shellfish

It's important to store and prepare fish and shellfish hygienically.

Storing:

  • 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.
  • Don't 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 don't close when you tap them. Live shellfish will "clam up" if their shells are tapped.

Preparing:

  • Wash your hands thoroughly before and after handling fish or shellfish.
  • Don't allow raw fish or shellfish or fluid from live shellfish to come into contact with cooked or ready-to-eat food.
  • Use separate utensils and plates for preparing raw fish and shellfish and other food.
  • Thaw 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 in Food allergy.

Medical Review: November 01, 2011

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