Omega-3 and omega-6: what they do and where to find them

Omega-3 and omega-6 are polyunsaturated fats. Your body can’t make some types of them, so it’s essential to get small amounts from your diet.

There are 3 main types of omega-3. ALA comes from plant foods, while EPA and DHA come mainly from oily fish. Your body can turn some ALA into EPA and DHA, but it happens slowly and only small amounts are made. The main omega-6 is linoleic acid, found in vegetable oils, nuts and seeds.

Eating oily fish is good for your heart. The NHS says the long-chain omega-3 in oily fish can help prevent heart disease, and it matters in pregnancy and breastfeeding because it helps a baby’s nervous system develop. The British Heart Foundation says omega-3 fats can help lower blood pressure and triglycerides, a type of fat in your blood.

The evidence for supplements is weaker:

• A large Cochrane review found that taking more omega-3, mostly from capsules, has little or no effect on deaths and at most a slight effect on heart disease, although it lowers triglycerides by about 15%.
• Another found no benefit for memory and thinking in healthy older people.
• The NHS says there’s little evidence for supplements in rheumatoid arthritis.

No. You may have read that omega-6 causes inflammation, or that you need a perfect ratio of omega-6 to omega-3. The British Heart Foundation says more recent evidence shows omega-6 fats don’t increase inflammation as part of a balanced diet, and European food safety experts chose not to set a ratio.

Swapping saturated fats for polyunsaturated fats, which include omega-6, can help lower “bad” LDL cholesterol. A Cochrane review found that eating more omega-6 lowers cholesterol and may reduce the risk of heart attacks.

A true deficiency is very rare. It causes rough, scaly skin, rather than the long lists of symptoms you may see online, and US health experts say it’s usually only seen in people fed through a drip that lacks polyunsaturated fats.

What’s common is not eating enough oily fish. The NHS says most of us don’t eat the recommended 2 portions of fish a week.

Good sources include:

• Oily fish, for omega-3: salmon, mackerel, sardines, herring, pilchards, sprats and trout.
• Vegetarian foods, for omega-3: walnuts, chia and pumpkin seeds, flaxseed (linseed), rapeseed oil, soya and omega-3 enriched eggs.
• Omega-6: vegetable oils such as sunflower, corn and rapeseed oil, spreads made from them, and nuts and seeds.

The NHS recommends at least 2 portions of fish a week, 1 of them oily. A portion is about 140g. Tuna doesn’t count as oily fish.

Oily fish can contain pollutants, so the NHS says some people should have no more than 2 portions a week. This includes girls, women who are planning a pregnancy or may have a baby one day, and women who are pregnant or breastfeeding.

If you’re pregnant or trying for a baby, don’t eat shark, swordfish or marlin, and have no more than 4 cans of tuna or 2 tuna steaks a week.

The British Dietetic Association and the British Heart Foundation don’t recommend omega-3 supplements for most people, because the evidence for them is inconclusive and the benefits come mainly from food. If you don’t eat fish and want to take one:

• Choose an omega-3 or fish oil supplement, not fish liver oil, which is high in vitamin A.
• Don’t have more than 1.5mg of vitamin A a day from food and supplements combined.
• Don’t take cod liver oil or any supplement containing vitamin A if you’re pregnant or trying for a baby.
• If you’re vegetarian or vegan, an algae oil supplement is an option.
• Check with a doctor first if you take any medicines. Omega-3 can interact with the blood thinner warfarin.

Read more in “How do I know if I’m low on vitamin D?”

A blood test measures the omega-3 and omega-6 fats in your blood, which gives a picture of what you’ve been eating. A test on red blood cells reflects your intake over roughly the last 4 months.

There are no agreed normal ranges, and there’s no level known to cause problems, so a result can’t diagnose a condition or tell you your risk of heart disease. It can give you a picture of your recent intake, and show how it changes if you change your diet.

Better2Know offers:

• Omega 3 / Omega 6: a home test that measures the omega-3 and omega-6 fats in a blood sample.
• Omega-3 and Omega-6 Fatty Acids: the same measurement, with your blood sample taken at one of our clinics.

Not sure which test you need? Our Patient Care Team is available 24/7 on 020 7099 0955.

Is cod liver oil the same as fish oil?

No. Fish liver oils are high in vitamin A, because fish store vitamin A in their livers. Too much vitamin A over many years can be harmful, and you should avoid fish liver oil if you’re pregnant or trying for a baby.

Can vegetarians and vegans get enough omega-3?

Plant foods such as walnuts, chia seeds, flaxseed and rapeseed oil contain ALA, but your body only turns a small amount into EPA and DHA. An algae oil supplement contains DHA, and some also contain EPA. It’s suitable for vegans.

Do omega-3 supplements help with depression?

A Cochrane review found a small effect, but said it was unlikely to make a meaningful difference to people with depression.

Omega-3 and omega-6 are both essential, and most people get plenty of omega-6. The simplest way to get enough omega-3 is to eat oily fish once a week, with at least one other portion of fish. Most people don’t need a supplement.

Order an Omega 3 / Omega 6 home test, or book the test at a clinic near you. Our Patient Care Team is available 24/7 on 020 7099 0955.

Not in the UK? Choose your country from the selector at the top of the page for local tests and prices.

This article originally appeared on 29 September 2023 and was last updated on 1 October 2026.

This article is general information and not a substitute for personal medical advice.

Sources

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7. NHS, Rheumatoid arthritis: treatment, reviewed 8 March 2023. https://www.nhs.uk/conditions/rheumatoid-arthritis/treatment/
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