Omega-3 fatty acids: what they do, and how much you actually need

Omega-3 gets talked about so much in health content that it is easy to lose track of what it actually is, what the different types do, and how much you need to eat or supplement to meet the recommended intake. This guide fixes that — without the marketing spin.

What omega-3 is

Omega-3 is a small family of polyunsaturated fatty acids that the body cannot make from scratch. They have to come from food. Three of them matter for human nutrition:

• ALA (alpha-linolenic acid) — the plant-based omega-3. Found in flax seeds, chia, walnuts, hemp, and rapeseed oil.
• EPA (eicosapentaenoic acid) — the marine omega-3. Found in oily fish, shellfish, and certain algae.
• DHA (docosahexaenoic acid) — the other marine omega-3. Same sources, with DHA especially concentrated in fish roe and algal oils.

The body can convert ALA into EPA and DHA, but very inefficiently. A landmark stable-isotope study in young women estimated net fractional ALA conversion at roughly 21% to EPA, 6% to DPA and 9% to DHA ^[1]; in men the conversion to DHA is markedly lower still, and a typical Western diet (high in linoleic acid) suppresses it further. If your goal is to reach the authorised health-claim thresholds for EPA and DHA, you want EPA and DHA directly, not ALA by itself.

Why EPA and DHA matter — the authorised claims version

In plain regulatory terms, under the EU and UK Nutrition and Health Claims registers ^[3]:

• EPA and DHA contribute to the normal function of the heart — at a daily intake of 250 mg combined EPA and DHA.
• DHA contributes to the maintenance of normal brain function — at a daily intake of 250 mg DHA.
• DHA contributes to the maintenance of normal vision — at a daily intake of 250 mg DHA.
• For pregnant and breastfeeding women, maternal intake of DHA contributes to the normal brain and eye development of the fetus and breastfed infant — at a daily intake of 200 mg DHA on top of the omega-3 baseline.

These are the statements that have passed formal EU scientific review, and they are the only EPA/DHA claims a food supplement is permitted to make in this register. Beyond them, the research literature is broader — you will find studies looking at triglyceride levels, inflammatory markers, mood, skin barrier function, and more. Some of that research is interesting; some is preliminary; none of it translates into an authorised product claim yet.

How much do you need

The baseline threshold for the heart, brain, and vision claims is 250 mg combined EPA and DHA per day. That is the minimum worth aiming for in most adults — and the figure most international health authorities use as an everyday target.

Higher intakes are sometimes appropriate — for example, women trying to conceive, during pregnancy, or for people whose doctors have recommended higher amounts for specific reasons. Discussing those situations with a healthcare professional is the sensible way to set a dose, not following social-media advice.

Food versus supplement maths:

• A 100 g serving of wild salmon contains roughly 1.2–2.2 g of combined EPA and DHA.
• A 100 g serving of sardines contains roughly 1.4 g.
• A 100 g serving of mackerel contains roughly 2.0 g.
• A tablespoon of flax oil contains around 7 g of ALA — but only a few percent converts to EPA and DHA.

The UK government broadly recommends two portions of fish per week, at least one of them oily. That is the food-based path to meeting the 250 mg EPA+DHA threshold. The NHS Eatwell guidance lines up with the same recommendation ^[4].

If you do not eat oily fish twice a week — and UK national diet surveys suggest most adults do not — a supplement is a practical alternative.

ALA on its own is not enough

ALA gets positioned as a "plant-based alternative" to fish oil. The truth is narrower. ALA has its own authorised health claim ("ALA contributes to the maintenance of normal blood cholesterol levels" at 2 g per day) ^[3], but for the heart, brain, and vision claims, ALA is not a substitute for EPA and DHA — because the body converts it so inefficiently ^[1].

If you follow a plant-based diet and want to reach the EPA+DHA thresholds, algae oil is the direct, vegan-suitable option. Algae are where marine EPA and DHA originate in the first place — fish just eat algae and concentrate the result.

Chemical form: triglyceride versus ethyl ester

One label detail that matters: the chemical form the omega-3 is supplied in.

Triglyceride form (TG, or rTG) is the structural form present in fish tissue, and the form the human digestive system is built to handle. Lipases — the enzymes that digest fat — work on triglycerides efficiently.

Ethyl ester form (EE) is produced when manufacturers concentrate the oil by replacing the glycerol backbone with ethanol. Cheaper to make, higher concentration achievable, but less efficiently absorbed by the body.

Re-esterified triglyceride (rTG) is a processing step that converts ethyl esters back into triglycerides. More expensive, but delivers the absorption profile of the natural form with the concentration of the processed form. In a head-to-head trial in 72 volunteers, EPA+DHA bioavailability was about 124% from re-esterified triglycerides versus natural fish oil, while ethyl esters came in at roughly 73% ^[2].

Algae oil is typically supplied natively in triglyceride form.

For a deeper walk-through on form, source and purity markers, see our omega-3 buying guide.

When supplementation makes practical sense

Situations in which a supplement is a reasonable move:

• Diet low in oily fish. If two portions of sardines, mackerel, salmon or herring per week is not happening, supplementation closes the gap.
• Plant-based diet. Algae oil delivers EPA and DHA without animal sources.
• Cost-conscious. Consistent supplementation at the 250 mg threshold is often cheaper than two portions of wild oily fish per week.
• Known preference for avoiding fish taste or reflux. A quality capsule in the right form avoids the fish-burp problem that puts people off supplementation.
• Pregnancy, breastfeeding, or planning a pregnancy. Discuss with a midwife or GP — algal DHA is often the cleanest option.

How to take it

• Take with a meal that contains fat. EPA and DHA are fat-soluble. A capsule taken with a fat-free snack delivers less to your bloodstream than one taken with breakfast that includes eggs, olive oil, or avocado.
• Keep the bottle cool, dark, and sealed. Omega-3 oils oxidise with heat, light, and air. Do not leave the bottle on a sunny windowsill.
• Do not cook omega-3 oils at high heat. Flax oil, in particular, should not be used for frying — heat destroys the ALA. Omega-3 supplements already inside a capsule are stable; the issue is cooking oils sold as omega-3 sources.

Our two omega-3 options

• Omega-3 fish oil capsules — high EPA and DHA per serving from small cold-water oily fish.
• Omega-3 algae oil — life'sOMEGA — 600 mg DHA and 200 mg EPA per serving from sustainable algal fermentation; fully vegan.

Both clear the 250 mg EPA+DHA daily threshold comfortably with the recommended serving, and both deliver their omega-3 in triglyceride form for natural digestion.

In practice

Omega-3 is one of the more straightforward supplement categories once you understand the three-letter codes. EPA and DHA do the heavy lifting for the authorised heart, brain, and vision claims; ALA has its own, narrower role. The 250 mg EPA+DHA daily threshold is the number to aim for. Two portions of oily fish per week will cover it from food; if that is not realistic in your week, a quality supplement closes the gap without fuss.

References

1. Burdge GC, Wootton SA. Conversion of alpha-linolenic acid to eicosapentaenoic, docosapentaenoic and docosahexaenoic acids in young women. Br J Nutr. 2002;88(4):411–420. PubMed: 12323090
2. Dyerberg J, Madsen P, Møller JM, Aardestrup I, Schmidt EB. Bioavailability of marine n-3 fatty acid formulations. Prostaglandins Leukot Essent Fatty Acids. 2010;83(3):137–141. PubMed: 20638827
3. European Commission. EU Register of Nutrition and Health Claims Made on Foods. ec.europa.eu
4. NHS. Fish and shellfish — nutrition and food types. nhs.uk

---