Omega-3 fatty acids are a group of polyunsaturated fats used by the body in cell membranes, signalling pathways, brain and eye development, inflammation control, and cardiovascular function. The main omega-3 fatty acids discussed in nutrition are alpha-linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid.
The body cannot make alpha-linolenic acid, so it must come from food. It can convert a small amount of alpha-linolenic acid into eicosapentaenoic acid and then docosahexaenoic acid, but the conversion is limited. For that reason, marine sources of eicosapentaenoic acid and docosahexaenoic acid are treated separately from plant sources of alpha-linolenic acid.
Types
- Alpha-linolenic acid, usually shortened to ALA, is found mainly in plant foods such as flaxseed, chia seed, walnuts, rapeseed oil, and soya.
- Eicosapentaenoic acid, usually shortened to EPA, is found mainly in oily fish, seafood, fish oil, krill oil, and some algal products.
- Docosahexaenoic acid, usually shortened to DHA, is found mainly in oily fish, seafood, fish oil, and algal oil. It is an important structural fat in the brain and retina.
Dietary Sources
Oily fish is the richest common dietary source of EPA and DHA. Examples include salmon, sardines, mackerel, herring, trout, anchovies, and pilchards. Fresh, frozen, and tinned oily fish can all contribute, although salted and brined products may add a lot of salt.
Plant sources provide ALA rather than EPA and DHA. Useful plant sources include:
- Flaxseed and flaxseed oil.
- Chia seeds.
- Walnuts.
- Rapeseed oil.
- Soya beans and soya oil.
- Some omega-3 enriched eggs or fortified foods.
Algal oil can provide DHA and sometimes EPA without fish, which makes it relevant for vegan diets.
Health Roles
Omega-3 fats are part of normal nutrition. They are involved in:
- Cell membrane structure.
- Heart and blood vessel function.
- Brain and eye development.
- Regulation of inflammatory signalling.
- Production of signalling molecules derived from fatty acids.
The strongest public health guidance is food-based. NHS guidance recommends at least two portions of fish a week, including one portion of oily fish. This advice is about overall diet rather than using fish as a medicine.
Supplements
Omega-3 supplements include fish oil, cod liver oil, krill oil, and algal oil. They vary widely in EPA and DHA content. A capsule labelled as fish oil does not necessarily contain a high dose of EPA or DHA.
Supplements are not the same as eating fish. Fish provides protein, vitamin D, iodine, selenium, and other nutrients as well as omega-3 fats. Cod liver oil also contains vitamin A and vitamin D, which matters because too much vitamin A can be harmful, especially during pregnancy.
Prescription omega-3 products are used in some settings for very high triglycerides, but that is different from general food supplements. Evidence for ordinary over-the-counter fish oil supplements is mixed and depends on dose, population, and outcome studied.
Safety
Food sources of omega-3 fats are suitable for most people as part of a balanced diet. There are limits for some fish because of mercury or pollutants. NHS guidance gives particular limits for shark, swordfish, marlin, tuna, and oily fish during pregnancy or when trying to become pregnant.
High-dose omega-3 supplements can interact with anticoagulant or antiplatelet medicines and may not be suitable for everyone. They can also cause indigestion, fishy aftertaste, nausea, or loose stools. Product quality varies, so the amount of EPA and DHA should be checked rather than relying on the size of the capsule.
See Also
References
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