Omega-3. How to get enough: A Dietitian's Guide

Sophie Mumby, Registered Dietitian (HCPC)

Omega-3 is something that I get asked a lot about during my clinics, especially during pregnancy. There is a vast amount of confusing information online and wading through the information can be confusing.

What are Omega-3 fatty acids?

Omega-3 fatty acids are a type of polyunsaturated fatty acid. There are three main types of omega-3 fatty acids; EPA (eicosapentaenoic acid), DHA (docosahexaenoic acid) and ALA (alpha-linoleic acid). The difference between the three is the number of carbon atoms that they contain; ALA containns 18 carbon atoms, whereas EPA and DHA are considered long-chain fatty acids as they contain 20 and 22 carbon atoms respectively. ALA cannot be produced by our body and is therefore an essential fatty acid. We can convert very small amounts of ALA into DHA and EPA in our body, but this is limited, so dietary sources of these fatty acids are important.

Why do we need them in our diet?

Omega-3 fatty acids play an important role in the structure of our cell membranes particularly in the retina (eyes), brain and sperm, they also have a wide ranging function in the body's cardiovascular, pulmonary, immune and endocrine systems.

Research indicates that DHA and EPA can also help lower triglyceride levels (fat in the blood) and improve blood pressure and heart rhythm.

Omega-3's in pregnancy are vitally important as they are needed to build the fetal brain, nervous system and retina. There is also a link between higher doses of omega-3 and a reduction in preterm births in those who are at high risk.

Where do they come from?

EPA and DHA are found in particuarly high levels in the flesh of oily fish. The fish obtain these fatty acids through their consumption of algae and seaweed. fl

Examples of oily fish include:

- Herring

- Pilchards

- Salmon

- Sardines

- Mackerel

Crab and Oyster are also good dietary sources of EPA+DHA but in smaller amounts than oily fish.

ALA is found in plant sources (including flaxseed, chia seeds and walnuts). Very small amounts of ALA can be converted to EPA and DHA within the body, but this is not enough to meet your long-chain omega-3 needs.

How much do I need?

There is no specific UK government recommended daily intake for EPA and DHA. UK advice instead recommends eating at least 2 portions of fish per week, including 1 portion of oily fish (around 140g). Oily fish are particularly rich sources of the long-chain omega-3 fatty acids EPA and DHA. The European Food Safety Authority (EFSA) has established an Adequate Intake of 250mg EPA+DHA per day for adults. This is equivalent to 1,750mg per week, although the recommendation is expressed as a daily intake rather than a weekly target. The problem with giving a specific figure is that it is difficult to quantify exactly how much omega-3 is in a specific fish; for example in salmon the omega-3 content will vary depending on whether it is wild or farmed and what it has been fed. However, as a rough guide we can use The McCance and Widdowson's composition of foods integrated database (CoFID) to give the following estimated EPA+DHA amounts per 140g portion of uncooked fish:

Salmon, farmed: 3038mg

Salmon, wild: 2338mg

Sardines: 1554mg

Mackerel: 3570mg

Herring: 1680mg

Cod: 98mg

Pollock: 182mg

As you can see, oily fish are particularly rich sources of EPA and DHA, with a 140g portion providing substantially more EPA+DHA than most white fish. 1-2 portions will therefore meet the EFSA recommended adequate intake values.

What about if I don't eat fish?

People may not eat fish for a multitude of reasons including vegetarianism, veganism, allergy, taste preferences or ethical concerns. Another option (if you eat them) of increasing the EPA and DHA in your diet is through eggs. Eggs also contain small amounts of DHA. For example, 100g of chicken egg provides around 60mg DHA in some food-composition databases. Two medium eggs would therefore provide roughly 60–70mg DHA, although the amount varies between eggs. Some omega-3-enriched eggs contain considerably more DHA because the hens are fed omega-3-rich feed such as flaxseed. It is important to remember that although these eggs are a useful source of DHA they do not contain significant amounts of EPA.

Fish can also be quite expensive, especially as we are recommending to eat it at least twice per week. Fish doesn't need to be fresh, in fact frozen and canned varieties are just as good and are often much cheaper than the fresh varieties.

If you are able to consume fish but prefer not to; a fish oil supplement may be recommended to meet your long-chain omega-3 requirements. If you are unable to consume fish due to allergies or dietary preferences a vegan alternative made from algae may be a good alternative.

What about in pregnancy and breastfeeding?

As mentioned long-chain omega-3 fatty acids are vital during pregnancy however there are some considerations to take in regards to fish safety during pregnancy. Certain fish need to be avoided during pregnancy due to their high levels of mercury and other toxins;

- Shark, swordfish and marlin need to be completely avoided

- Oily fish needs to be limited to no more than 2x 140g portions per week

- Tuna needs to be limited to a maximum of 4 cans or 2 tuna steaks per week

- White fish can be eaten freely

- Avoid fish liver supplements (e.g. cod liver oil) as this contains large amounts of vitamin A which can be harmful for the baby

During pregnancy there is again no official guidance on dosages for omega-3 fatty acids in the UK however the NHS recommends that 1-2 portions of oily fish (~140g) is enough to meet your needs. The European Food Safety Authority (EFSA) recommends an intake of 250 mg/day of EPA+DHA for adults with an additional 100–200 mg/day of preformed DHA during pregnancy (2450-3150mg/week). This dose can therefore be met with 1-2 portions of oily fish per week (140g of salmon, sardines or mackerel).

A 2018 Cochrane review of 70 randomised controlled trials involving almost 20,000 pregnant women found that increasing long-chain omega-3 intake during pregnancy reduced the risk of preterm birth before 37 weeks by 11% and early preterm birth before 34 weeks by 42%. It also found fewer babies with low birthweight, although omega-3 supplementation was associated with a small increase in pregnancies continuing beyond 42 weeks. The review authors suggested that pregnant women could consider 500–1000mg of long-chain omega-3 per day from around 12 weeks of pregnancy, with at least 500mg as DHA. This is an evidence-based interpretation from the review authors rather than current UK government guidance. If you have any concerns about your own pregnancy please speak with your midwifery team who can guide you in your specific circumstances.

What about Grass-Fed Beef?

Grass fed beef seems to be quite prominent on social media at the moment with claims about it's omega-3 content. Grass contains ALA, which contributes to the omega-3 content of the animals' diet. Some of this will then contribute to the omega-3 fatty acid content of beef. Therefore grass-fed beef does contain omega-3 fatty acids, including ALA, EPA and DHA, and generally provides more omega-3 than grain-fed beef. However, the amount is considerably lower than that found in oily fish. A 2021 study found that grass-fed beef provided about 17.5 mg EPA+DHA per 100 g, compared with about 10.5 mg in grain-fed beef. Which is much lower than the EPA+DHA levels found in oily fish which is measured in the thousands of mg/100g and shows why grass-fed beef should not be considered a major dietary source of omega-3 fatty acids.

A 2026 update

You may have seen in the news recently about a change in some tins of mackerel in UK supermarkets. Some supermarkets including Sainsburys, Tesco and Lidl have swapped some of the mackerel in their tins to Jack Mackerel due to concerns about fishing sustainability. Jack mackerel is an entirely different species of fish and is thought to contain much lower levels of DHA+EPA. So just bear that in mind when choosing your weekly sources of omega-3 that some UK tins of mackerel may not be providing you with as much as you first thought.

A closing thought

Omega-3 fatty acids are an important part of our diet, particularly if you are pregnant or breastfeeding. For most people 1-2 portions of oily fish per week meets your needs. If you are unable to eat enough fish supplements play an important role.

This article is intended for general education and does not replace individual dietetic assessment, medical advice or mental-health care. If any of this resonates with you or someone you know, please reach out for personalised support.

References

EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific Opinion on Dietary Reference Values for fats, including saturated fatty acids, polyunsaturated fatty acids, monounsaturated fatty acids, trans fatty acids, and cholesterol. EFSA Journal. 2010;8(3):1461. doi:10.2903/j.efsa.2010.1461.

NHS. Fish and shellfish. NHS website.

NHS. Healthy eating in pregnancy. NHS website.

Nogoy KMC, Sun B, Shin S, Lee Y, Zi Li X, Choi SH, Park S. Fatty Acid Composition of Grain- and Grass-Fed Beef and Their Nutritional Value and Health Implication. Food Sci Anim Resour. 2022 Jan;42(1):18-33. doi: 10.5851/kosfa.2021.e73. Epub 2022 Jan 1. PMID: 35028571; PMCID: PMC8728510.

Office for Health Improvement and Disparities. McCance and Widdowson's Composition of Foods Integrated Dataset (CoFID) 2021. GOV.UK.

Middleton P, Gomersall JC, Gould JF, Shepherd E, Olsen SF, Makrides M. Omega-3 fatty acid addition during pregnancy. Cochrane Database of Systematic Reviews. 2018;11:CD003402. doi:10.1002/14651858.CD003402.pub3.

U.S. Department of Agriculture, Agricultural Research Service. USDA National Nutrient Database for Standard Reference, Release 28: Fish, mackerel, jack, canned, drained solids (NDB No. 15048).

National Institutes of Health, Office of Dietary Supplements. Omega-3 Fatty Acids: Fact Sheet for Health Professionals.