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Omega-3

/əʊˌmeɪ.ɡə ˈθriː/ · oh-MAY-guh THREE noun

Also: omega-3 fatty acids, n-3 fats

A family of polyunsaturated fatty acids named after the position of their first double bond. The three most discussed are ALA (from plants) and EPA and DHA (mainly from oily fish and algae).

What it is and how it works

Fats are built from fatty acids, chains of carbon atoms of different lengths. In a polyunsaturated fat, the chain has several double bonds. "Omega-3" means the first of those double bonds sits on the third carbon counted from the omega, or tail, end of the chain. It is chemistry shorthand that became an everyday word.

Three omega-3s come up most often:

  • ALA (alpha-linolenic acid) is found in plants. The body cannot make it, so it is an essential fatty acid that has to come from food. ALA contributes to the maintenance of normal blood cholesterol levels, a role that applies to foods providing a meaningful amount of it (the official condition is 2 g of ALA per day).
  • EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are longer chains found mainly in oily fish and seafood, and in some algae. The body can convert a small proportion of ALA into EPA and DHA, but the conversion is limited.

EPA and DHA are built into cell membranes throughout the body, with DHA particularly concentrated in the brain and the retina.

Plate of baked salmon with boiled potatoes and green beans on a kitchen table
A salmon fillet with potatoes and green beans. Oily fish is the main food source of EPA and DHA.

Recognised roles

In the European Union, a small number of statements about omega-3 are authorised, each with a condition:

  • EPA and DHA contribute to the normal function of the heart. The beneficial effect is obtained with a daily intake of 250 mg of EPA and DHA.
  • DHA contributes to the maintenance of normal brain function and normal vision, with a daily intake of 250 mg of DHA.
  • ALA contributes to the maintenance of normal blood cholesterol levels, with a daily intake of 2 g of ALA.

These conditions describe when the statement applies; they are not personal recommendations.

Where it is found

  • Oily fish: salmon, mackerel, sardines, herring, trout and anchovies. Oily fish is also one of the few natural food sources of vitamin D. Many food guides suggest one portion of oily fish a week as part of two fish meals.
  • Plant sources of ALA: flaxseed (linseed) and its oil, chia seeds, hemp seeds, walnuts, rapeseed (canola) oil and soy.
  • Algae-based products: a source of EPA and DHA for people who do not eat fish.

In everyday life

  • Tinned fish counts. Sardines and mackerel in tins are inexpensive and keep well.
  • Ground flaxseed on porridge or yoghurt adds ALA; whole seeds tend to pass through undigested.
  • A handful of walnuts as a snack or in a salad.
  • Cooking oil: rapeseed oil provides some ALA and suits everyday cooking.

Common confusions

"Plant omega-3 and fish omega-3 are the same." They are related but different. ALA is converted only partly into EPA and DHA.

"More fish oil is always better." High intakes are not automatically more useful, and fish oil supplements can interact with blood-thinning medication. Anyone taking medication, or who is pregnant, should ask a doctor or pharmacist before using supplements.

"Omega-3 and omega-6 are opposites." Both are essential polyunsaturated fats. The idea of a perfect ratio between them is still debated; eating more oily fish, nuts and seeds and fewer ultra-processed foods is the practical message.

"All fish are equally rich." White fish such as cod contains much less omega-3 in its flesh than oily fish.

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Added Oct 02, 2026 · Filed under Food & nutrients