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Omega-3: functions, foods, deficiency and supplements

Find out all about omega-3, including what it does, how much you need, where to find it, and who might need to supplement their diet

What is omega-3?

Omega-3 is a type of polyunsaturated fatty acid. There are three types of omega-3 fatty acids:

  • ALA (alpha-linolenic acid)
  • EPA (eicosapentaenoic acid)
  • DHA (docosahexaenoic acid)

We have to get all our omega-3 fatty acids from food. Good food sources include nuts and flaxseed oil (ALA) and oily fish, shellfish and marine algae (EPA and DHA).2 

You might need to take an omega-3 supplement if you don’t eat fish, are vegetarian or vegan.

Top omega-3 benefits

Some of the best omega-3 fish oil benefits include supporting healthy:1

  • blood cholesterol
  • blood pressure
  • brain function
  • vision
  • children’s growth and development

What does omega-3 do in the body?

Here’s what each type of omega-3 essential fatty acid does inside the body:3

ALA: needed for children’s normal growth and development, and helps maintain normal blood levels of cholesterol

DHA: contributes to the normal function of the heart, helps maintain normal blood pressure, and blood levels of triglycerides, a type of fat in the blood. It also contributes to normal brain development and vision, and baby’s brain and eye development during pregnancy

EPA: like DHA, it helps maintain normal blood pressure and blood levels of triglycerides level

ALA is the only type of omega-3 that can’t be made in our body, so we need to make sure we get enough in our diet.

In a pinch, the body can convert ALA into EPA and DHA – though this takes time and doesn’t produce much. So, dietitians advise us to eat foods containing EPA and DHA, like oily fish.4

We need a balance of fats in our diet to stay healthy; an excess of omega-6 fatty acid – another essential fatty acid that our bodies need to source from food – compared to omega-3 can lead to:

  • obesity
  • inflammation5

Omega-6 is found in vegetable oils, margarine, breads, cakes and biscuits, so it’s best to cut down on processed foods to help reduce your intake, while at the same time upping your intake of omega-3 foods, like oily fish.6

How much omega-3 do I need?

There is no recommendation for omega-3 in UK, though most of us get enough ALA from our food.

However, many people don’t eat enough EPA or DHA, so the UK government advises two portions of fish a week – one of which should be an oily fish7 – or about 450mg of EPA and DHA a day.8

How much omega-3 do children need?

To get enough EPA and DHA, children should eat the following portions of oily fish every week:9

  • 18 months-3 years – ¼ – ¾ small fillet
  • 4-6 years – ½ to 1 small fillet
  • 7-11 years – 1 – 1 ½ small fillets

If your child is vegetarian or vegan – don’t worry! Read below to find out more about vegetarian and vegan sources of omega-3, as well as how to supplement omega-3 for kids.

Omega-3 foods

Foods high in omega-3 vary from seafood to soya products, so whatever your diet, you can make sure you’re getting all the omeaga-3 you need.

Animal sources of omega-3

Eating oily fish is one of the easiest ways to get the omega-3 you need.

However, as some fish stocks are declining (like wild salmon and trout) it is important to choose sustainable sources of fish, where possible.

When you are next shopping for fish, look for the Marine Stewardship Council (MSC) certified products or look up Marine Conservation Society’s ‘The Good Fish Guide’.10

The best animal food sources of omega-3 include:

  • mackerel
  • herring (kippers)
  • trout
  • salmon
  • sardines
  • crab
  • anchovies
  • bloater
  • carp
  • eel
  • pilchards
  • sprats
  • swordfish
  • whitebait

Including these oily fishes in your diet is good for you in other ways too. They’re a good source of vitamin A, vitamin D and B vitamins, as well as the minerals calcium, iodine, iron, zinc and selenium.

Can you eat too much oily fish?

Some fish contain trace amounts of metals or chemicals that might be harmful if you eat too much.

Generally, it’s safe to eat up to 4 portions of oily fish per week, except if you’re pregnant, breastfeeding or likely to become pregnant any time soon. If so, it is advised that you eat no more than 2 portions a week.

However, there are types of fish certain people need to limit their intake of:11

  • Marlin, swordfish and shark may contain concentrated sources of mercury that may be dangerous for a developing baby’s nervous system. So, it is advised that all children under 16, pregnant women and those planning for a baby should avoid them.
  • All other adults (including breastfeeding women) can consume a maximum of one portion of these fish a week.

Vegetarian omega-3 sources

If you don’t want to eat fish to get your fill of omega-3, don’t worry. There are plenty of vegetarian sources of omega-3, including fortified omega-3 products, like certain brands of: 12, 13

  • eggs
  • milk
  • yoghurt
  • bread
  • spreads

Find more vegetarian sources of omega-3 in the vegan section below.

Vegan omega-3 sources

You can get all the omega-3 you need from eating a variety of plant sources – you just need to make sure you’re getting the right mix of ALA, EPA and DHA.

The best omega-3 vegan foods include:

Nuts and seeds

  • ground flaxseeds
  • walnuts
  • almonds
  • pecans
  • peanuts

Vegetable oils

  • rapeseed oil
  • flaxseed oil

Soya products

  • edamame beans
  • tofu
  • soy milk

Green leafy vegetables

  • kale
  • spinach
  • broccoli
  • cauliflower
  • brussels sprouts


Algae is the only vegetarian and vegan source of omega-3 that contains EPA and DHA.

While most of the above foods are great sources of ALA (which a little can be converted into EPA and DHA, different algae are full of both EPA and DHA. It’s where the fish get it from in the first place.

So ,vegan or not, make sure to include some seaweed and other microalgae in your diet, or consider taking an algae supplement or other vegan omega-3 supplement to make sure you’re getting those DHAs!

Read more Vegan sources of Omega-3 here

What are the benefits of taking an omega-3 supplement?

A 2011 US study reported that 3g or more of omega-3 a day can reduce the levels of fat, such as triglycerides, in your blood.20 

A 2012 report in Advances in Nutrition found that EPA and DHA supplementation can help keep arteries functioning normally.21 

Scientists are also examining the role of omega-3 supplements in brain health – in particular with regards to ageing and mood – although more studies need to be done.22

Do pets need omega-3?

Should you be providing omega-3 for cats? Is an omega-3 supplement for dogs recommended? It turns out your furry pals need omega-3 fatty acids to thrive, just like us.

Whether they get it through their food or supplement, omega-3 offers several key health benefits to your cats and dogs:23

  • Reduced inflammation: EPA and DHA act as cellular signals in the body to reduce inflammation. It may help your pets manage diseases like arthritis and heart disease, as well as reducing itchiness from skin allergies.
  • Improved brain function: DHA helps our pet’s brains develop and function, so from ‘playing dead’ to impressing us on agility courses, omega-3 could be great for your pet’s cognitive functions. It can also help reduce the effects of cognitive dysfunction in dogs, which is similar to dementia in people.
  • Slowed tumour growth: DHA has been shown to promote cancer cell differentiation, meaning that cells can’t continue to divide, and the tumour cannot continue to grow.


How much omega-3 do pets need?

Your dog’s and cat’s food should already contain omega-3s from fish or supplements – just make sure you check the label.

If you make your own pet food, please consult your vet to check they are getting enough or if they may need a supplement.

Which foods have omega 3 6 9, and what is the difference?

It’s important to consume omega-3, 6 and 9. We have already talked about omega-3, so here’s a little information on omega-6 and omega-9:14

  • Omega-6: like omega-3s, omega-6s are polyunsaturated fatty acids. They’re mostly used for energy and you can find them in foods like sunflower seeds, peanut butter, avocado oil, eggs, safflower oil and tofu.
  • Omega-9: these fatty acids are monounsaturated and produced quite easily by our bodies. Food sources of it include olive oil, almond oil, avocado oil, almonds, cashews and walnuts.

As you can see, some foods are rich in all 3 omega-3 fatty acids, especially vegan omega 3, 6, 9 sources.

Omega-3 deficiency

What are the symptoms of an omega-3 deficiency?

  • dry skin, hair and nails
  • insomnia
  • difficulty concentrating
  • stiff joints
  • fatigue15

What happens if I consume too much omega-3?

Up to 5000mg per day of omega-3 is safe, according to the European Food Safety Authority.16 However, we only need a tenth of this.

If you take more than this, there are risks of:

  • excessive bleeding or blood thinning
  • impaired regulation of blood glucose levels
  • reduced immune function17

Omega-3 supplements

When should I take omega-3 supplements?

Most people can get enough omega-3 from their diet, but if you don’t like fish, or are vegetarian or vegan, you might need an omega-3 supplement.

Which vegan omega-3 supplements are available?

Algal oil is the vegan equivalent of fish oil. Eating algae is how fish get their omega-3!

Don’t take omega-3 fish oil supplements if you are prescribed medication for high blood pressure to avoid any interaction.18

Should children take an omega-3 supplement?

Children should be able to get the omega-3 they need from eating oily fish. However, if they don’t like fish, omega-3 tablets or other supplements may help them reach their daily needs. Read the label to check it’s suitable for children and has a good mix of EPA and DHA.

Should women take an omega-3 supplement in pregnancy?

You should be able to get all the omega-3 you need from eating a balanced diet, but if you don’t like fish, are vegetarian or vegan, you may benefit from a supplement.

However, avoid:

  • fish liver supplements, like cod liver oil – it contains high levels of vitamin A, which could be harmful to your unborn baby
  • supplements containing more than 450mg of EPA and DHA a day – this has not been proven safe19

Last updated: 20 July 2021

Advice is for information only and should not replace medical care. Please check with your GP before trying any remedies.


  1. European Commission. EU Register on nutrition and health claims. Available from: http://ec.europa.eu/food/safety/labelling_nutrition/claims/register/public/?event=register.home
  2. Kat Gal. Medical News Today. What are the best sources of omega-3? Available from: https://www.medicalnewstoday.com/articles/323144.php
  3. As Source 1
  4. British Dietetic Association. Food Fact Sheet: Omega-3. Available from: https://www.bda.uk.com/foodfacts/omega3.pdf
  5. Simopoulos AP. An Increase in the Omega-6/Omega-3 Fatty Acid Ratio Increases the Risk for Obesity. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4808858/
  6. The European Food Information Council. The importance of omega-3 and omega-6 fatty acids. Available from: https://www.eufic.org/en/food-today/article/the-importance-of-omega-3-and-omega-6-fatty-acids
  7. British Nutrition Foundation. n-3 Fatty Acids and Health. Available from: https://www.nutrition.org.uk/attachments/156_n-3%20Fatty%20acids%20and%20health%20summary.pdf
  8. Sarah Schenker. Babycentre. Is it safe to take fish oil supplements in pregnancy? Available from: https://www.babycentre.co.uk/x541094/is-it-safe-to-take-fish-oil-supplements-in-pregnancy
  9. As Source 4
  10. https://www.heartuk.org.uk/low-cholesterol-foods/omega-3-fats
  11. https://www.bda.uk.com/resource/omega-3.html
  12. Great Western Hospitals NHS Foundation Trust. Omega 3 Fatty Acids and Heart Health. Available from: https://www.gwh.nhs.uk/media/31921/omega3_fatty_acids_and_heart_health.pdf
  13. Freydis Hjalmarsdottir. Healthline. 12 Foods that Are Very High in Omega-3. Available from: https://www.healthline.com/nutrition/12-omega-3-rich-foods
  14. https://www.healthline.com/nutrition/omega-3-6-9-overview#section3
  15. Jami Cooley. University Health News. Omega-3 Benefits and Deficiency Symptoms: Why You Need This Essential Fatty Acid. Available from: https://universityhealthnews.com/daily/nutrition/omega-3/
  16. European Food Safety Authority. EFSA assesses safety of long-chain omega-3 fatty acids. Available from: https://www.efsa.europa.eu/en/press/news/120727
  17. As above
  18. NHS Choices. Supplements Who Needs Them? Available from: https://www.nhs.uk/news/2011/05May/Documents/BtH_supplements.pdf
  19. As Source 8
  20. Shearer GC, Savinova OV, Harris WS. Fish oil – how does it reduce plasma triglycerides? Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3563284/
  21. Swanson D, Block R, Mousa SA. Omega-3 Fatty Acids EPA and DHA: Health Benefits Throughout Life. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3262608/
  22. Cutuli D. Functional and Structural Benefits Induced by Omega-3 Polyunsaturated Fatty Acids During Aging. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5543674/
  23. https://www.petmd.com/news/view/what-are-benefits-fish-oil-dogs-and-cats-37853
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