Flaxseed Oil vs Fish Oil: ALA vs EPA and DHA, Conversion and Evidence
Flaxseed oil supplies the plant omega-3 ALA; fish oil supplies EPA and DHA. See the documented differences, conversion limits and what trials compared, with no universal winner.
Content last updated . This page has not been medically reviewed.
What each oil supplies
ALA (alpha-linolenic acid) is found in plant oils such as flaxseed, soybean and canola, and in chia seeds and walnuts. [1] EPA and DHA are the long-chain omega-3 fats that oily fish are high in. [2] The body can make some EPA from ALA, but supplements of ALA have little effect on blood DHA. [3] For a fuller explanation see ALA, EPA and DHA and flaxseed oil and plant omega-3.What research compared
Official intake figures
EFSA (EU, 2012) judged 250 mg a day of EPA plus DHA adequate for general cardiovascular health in healthy adults and children. [8] That figure is for EPA and DHA, not ALA. An official adequate intake for ALA could not be verified: the NIH Office of Dietary Supplements site blocked our download and we did not quote it from memory. See RDA, AI, DV and UL.No universal winner
They are different nutrients. Food versions of flaxseed are on flaxseed, and fish is on oily fish.Frequently asked questions
Is flaxseed oil as good as fish oil?
Not interchangeable. Flaxseed oil provides ALA; fish oil provides EPA and DHA. [1] Trials show ALA mainly raises EPA, with little effect on DHA. [3]
Does the body turn flaxseed oil into DHA?
Only a little. A review found ALA supplements have little effect on blood DHA, while preformed DHA does. [3]
Which is better for the heart?
Cochrane found small or uncertain effects for both ALA and EPA/DHA on heart outcomes, with a roughly 15 percent triglyceride fall for EPA/DHA. [7] No direct comparison trial was found.
Can vegetarians use flaxseed oil instead?
It is an ALA source suitable for vegetarians. [9] For blood DHA, a scoping review found algal oil raised the omega-3 index while high-dose flaxseed oil did not. [4]
Is it safe to take either with medicines?
Ask a pharmacist, especially for blood thinners or before surgery. See medication interactions.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
How to read the evidence labels
Labels used on this page: mixed (studies disagree), promising but limited (few or small trials), biomarker only (a blood measure, not a health outcome).
| Question | What the source found | Label |
|---|---|---|
| Does ALA raise EPA and DHA in blood? | A review of studies in healthy adults eating Western diets found supplemental ALA raises EPA and DPA status, but ALA or EPA supplements have little effect on DHA, while preformed DHA does raise blood DHA. [3] | Biomarker only |
| Omega-3 index in vegetarians and vegans | A scoping review of 13 trials found high-dose flaxseed or echium seed oil gave no increase in the omega-3 index, and some studies showed reductions; microalgal oil raised it in all studies. [4] | Biomarker only |
| Four weeks of 4 g a day of ALA (flaxseed oil) vs DHA-rich fish oil, women with obesity | Fish oil raised EPA and DHA oxylipins; there were no changes after flaxseed oil. Neither reduced inflammatory markers. [5] | Biomarker only; study amount, not advice |
| Six months, type 2 diabetes, 3 g a day of perilla (ALA) oil vs fish oil | Perilla oil lowered fasting glucose while fish oil lowered triglycerides. [6] | Promising but limited; perilla is not flaxseed |
| Heart outcomes, increased ALA | Cochrane found increased ALA probably makes little or no difference to all-cause mortality and may slightly reduce cardiovascular events (relative risk 0.95, interval 0.83 to 1.07, low certainty). [7] | Mixed |
| Heart outcomes, increased EPA and DHA | The same review found little or no effect on all-cause mortality (relative risk 0.97, interval 0.93 to 1.01), but triglycerides fell by about 15 percent. [7] | Mixed; triglycerides are a blood measure |
Most trials in the Cochrane review lasted 12 to 88 months in adults at varying heart risk, mainly in high-income countries. [7] No trial in the sources we read compared flaxseed oil with fish oil on heart attacks or strokes: Proper evidence not found (we searched PubMed for ALA/flaxseed cardiovascular trials and read the Cochrane review).
Safety and who should ask first
- Side effects of omega-3 supplements are usually mild: taste, bad breath, headache, heartburn, nausea, diarrhea. [1]
- Fish oil carries bleeding, surgery and medicine-interaction questions; see fish oil, blood thinners and bleeding risk and medication interactions. Flaxseed-oil-specific cautions were not described in the sources we read here; the flaxseed page covers what it can.
- Pregnancy, breastfeeding, children, kidney or liver conditions and upcoming surgery: ask a clinician or pharmacist. Do not stop a prescribed medicine on your own.
- Vegetarians and vegans who want preformed DHA: see algal oil. NHS lists flaxseed oil among omega-3 sources suitable for vegetarians. [9]
- Product quality varies: quality testing and certifications.