ALA vs EPA vs DHA: The Three Omega-3s Explained
There are three omega-3 fatty acids you will encounter on supplement labels and in nutrition guidance: ALA, EPA, and DHA. They are all omega-3s, but that is roughly where the similarity ends. They have different chain lengths, come from different food sources, and your body handles them in fundamentally different ways.
The distinction matters because a product labelled "omega-3" could contain any of the three, and they are not interchangeable.
What ALA, EPA, and DHA Each Are
ALA (alpha-linolenic acid) is a short-chain omega-3 with 18 carbon atoms. It is the form found in plant foods: flaxseeds, chia seeds, walnuts, hemp seeds, and their oils. ALA is classified as an essential fatty acid because your body cannot synthesise it. You must get it from food.
EPA (eicosapentaenoic acid) is a long-chain omega-3 with 20 carbon atoms. It is found in oily fish and in certain microalgae, particularly Nannochloropsis. EPA is the primary precursor to eicosanoids, signalling molecules involved in the body's inflammatory response pathways.
DHA (docosahexaenoic acid) is a long-chain omega-3 with 22 carbon atoms. It is the dominant omega-3 in the brain and retina. DHA is found in oily fish and in algae oil from species like Schizochytrium.
The critical distinction: ALA is the precursor. EPA and DHA are the forms your body actually uses for the specific physiological functions cited in health claims. Your body can convert ALA into EPA and DHA, but the conversion rate is the central problem with relying on ALA alone.
When we formulated our EPA supplement, we chose Nannochloropsis specifically because it produces EPA as the dominant long-chain fatty acid, which is not the case for every marine microalgae species. That sourcing decision reflects the chain-length difference: the target is always the long-chain form your body uses directly, not the precursor.
The Conversion Problem
Your body converts ALA to EPA at an estimated rate of 5 to 15%. The conversion of ALA to DHA is even lower, generally under 5%. These figures vary with genetics, sex, age, diet composition, and overall health. They are consistent enough across the literature to establish the principle: most of the ALA you eat stays as ALA.
This is the reason the ALA-vs-long-chain debate matters to you practically. If you eat a tablespoon of flaxseed oil, you get roughly 7 grams of ALA. At a 10% conversion rate to EPA, that yields about 700 mg of EPA.
At a 3% conversion rate to DHA, that yields about 210 mg of DHA. Those numbers sound adequate until you consider that the conversion rate is not guaranteed, it varies day to day, and the lower end of the range produces considerably less.
We reviewed conversion trials during product development — studies showing ALA-to-EPA efficiency ranging from 3 to 15 per cent depending on sex, diet, and genetic background. The variance was the problem. A conversion pathway that delivers 3 per cent one week and 12 per cent the next cannot underpin a reliable dosing strategy. That observation drove the decision to use direct algae sources rather than ALA.
What the Health Claims Cover
The EFSA-authorised health claims for omega-3 are specific to EPA and DHA, not ALA (Commission Regulation (EU) No 432/2012):
- EPA and DHA contribute to the normal function of the heart (250 mg combined daily).
- DHA contributes to the maintenance of normal brain function (250 mg daily).
- DHA contributes to the maintenance of normal vision (250 mg daily).
ALA has its own authorised claim: "ALA contributes to the maintenance of normal blood cholesterol levels," at a daily intake of 2 g ALA. This is a different claim from the heart, brain, and vision claims attached to EPA and DHA. A product containing only ALA cannot carry the EPA/DHA health claims, even though all three are omega-3 fatty acids.
We list the complete authorised claims with conditions in our EFSA claims reference.
When ALA Is Enough and When It Is Not
ALA has genuine nutritional value. It is an essential fatty acid. The foods that contain it (flaxseeds, walnuts, chia seeds) are nutritious for many reasons beyond their omega-3 content. We are not arguing that ALA is worthless. We are arguing that ALA and EPA/DHA serve different purposes, and conflating them on a label misleads you about what you are getting.
If your goal is to meet the EFSA intake condition for the heart-function claim (250 mg combined EPA+DHA daily), ALA sources alone are unlikely to get you there reliably given the conversion rates. If you eat oily fish twice a week, the question is largely academic because you are getting EPA and DHA directly. If you are plant-based, the conversion bottleneck is the central challenge in your omega-3 strategy.
The direct answer: if you are plant-based and not eating algae, you are almost certainly not meeting EPA and DHA needs through ALA conversion. Eat the flaxseeds. Just do not count them as your EPA and DHA source.
The Plant-Based Solution
For people who do not eat fish, the most reliable route to adequate EPA and DHA is direct supplementation from algae sources. Marine phytoplankton from Nannochloropsis provides EPA. Algae oil from Schizochytrium provides DHA. These are the same fatty acids as in fish oil, sourced from the organisms that originally produce them.
We manufacture both: ULTANA Phytoplankton for EPA and Clean Omega DHA for DHA. The limitation is practical: fish oil delivers both fatty acids in a single product. With algae, you typically need two separate supplements, which adds cost and daily complexity. That is a genuine trade-off worth knowing before you buy. We explain the differences in function, dosing, and which conditions each supports in our EPA vs DHA comparison.
ALA-rich foods remain valuable as part of your overall diet. They provide fibre, minerals, and other nutrients alongside their omega-3 content. The issue is not that ALA is bad. The issue is that "omega-3" on a label does not tell you which type you are getting, and the type determines whether you are meeting the intake conditions for the health claims that matter to you.
What our research found
Species selection came down to batch consistency, not peak figures. When we reviewed compositional analyses during product development, Nannochloropsis gaditana showed consistent EPA concentrations across closed photobioreactor batches. Other marine species drifted more with temperature variation. For DHA, Schizochytrium's fermentation substrate kept the DHA-to-DPA fatty acid ratio predictable across production runs in a way photosynthetic species could not match. Reproducibility drove the decision.
Your genes determine how well you convert ALA. Variants in the FADS1 and FADS2 genes control desaturase enzyme activity. People carrying the TT genotype at a key variant (rs174537) have 23 per cent lower plasma EPA than those with the GG genotype. You cannot know your genotype from a label or a dietary plan, which is another reason the conversion route is unreliable for precise dosing.
High linoleic acid intake makes the conversion problem worse. ALA and linoleic acid (the omega-6 found in sunflower, corn, and soybean oils) compete for the same desaturase enzymes. A modern UK diet high in vegetable oils pushes that competition toward omega-6, reducing the already limited ALA-to-EPA pathway further. Eating more flaxseed does not solve the problem if the rest of your diet is saturated with competing omega-6.
Sources
- 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
- Burdge GC. Can adults adequately convert alpha-linolenic acid (18:3n-3) to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)? Int J Food Sci Nutr. 1998;49(S103):S103-S110. PubMed
- EFSA NDA Panel. Scientific Opinion on EPA, DHA, DPA: cardiac function, blood pressure, triglycerides. EFSA Journal. 2010;8(10):1796. EFSA
- Commission Regulation (EU) No 432/2012. Official Journal of the EU. L 136/1. EUR-Lex
- Lane K, Derbyshire E, Li W, Brennan C. Bioavailability and potential uses of vegetarian sources of omega-3 fatty acids: a review of the literature. Food Res Int. 2014;64:229-238. PubMed
Cara Hayes, MSc Nutrition and Dietetics (University of Sydney), writes all content in the Phytality Knowledge Centre. Read our editorial policy.
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Consult your healthcare provider before starting any supplement.
Methodology and Disclosure
Phytality manufactures EPA and DHA supplements from microalgae. We have a commercial interest in direct-source EPA and DHA supplementation and in the distinction between these and ALA. Conversion rate estimates (5-15% ALA to EPA, under 5% ALA to DHA) reflect published nutrition science across multiple studies.
EFSA health claims are cited from Commission Regulation (EU) No 432/2012 with stated intake conditions. The ALA cholesterol claim is separately authorised under the same regulation. Our editorial assessment of ALA adequacy reflects our review of the conversion literature and aligns with positions taken by major nutrition authorities.
Last reviewed: March 2026
