Health benefits of fish
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.
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 choose fish from sustainable sources
Types of fish
Different types of fish and shellfish provide different nutrients.
Oily fish are:
- rich in long-chain omega-3 fatty acids, which may help prevent heart disease
- a good source of vitamins A and D
The following are all oily fish:
- herring (bloater, kipper and hilsa are types of herring)
- jack (also known as scad, horse mackerel and trevally)
- tinned salmon
- fresh salmon
- canned sardines
- tuna (fresh)
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 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 also 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
Men and boys can eat up to four portions of oily fish a week.
Women and girls
Women and girls who may become pregnant in the future, or who are pregnant or breastfeeding, should eat up to two portions. This is because pollutants found in oily fish may affect the development of a baby in the womb in the future.
Women who won’t become pregnant in the future can eat up to four portions of oily fish a week.
Examples of white fish are:
- red mullet
- dover sole
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
You can safely eat as much of these types of white fish per week as you like.
Other white fish
Other white fish that may contain similar levels of certain pollutants as oily fish are:
- sea bream
- sea bass
- 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.
Shellfish includes prawns, mussels and langoustine.
- 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.
Shark, swordfish and marlin
Children, pregnant women and women who are trying to get pregnant should not eat these fish. 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 can damage a developing baby’s nervous system and cause health problems.
Advice on eating fish during pregnancy
During pregnancy, 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.
Avoid raw shellfish
When pregnant, you can reduce your risk of food poisoning by avoiding raw shellfish.
Shark, swordfish and marlin
As outlined above, do not eat these if you are pregnant or trying to get pregnant.
Limit 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.
Due to the low levels of pollutants that oily fish contain, it can build up in the body and may harm an unborn baby during a future pregnancy.
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.
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.
Children and babies over six months
As explained above, you should avoid giving your children 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.
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.