Fish Oil vs Flaxseed Oil: EPA, DHA and ALA | Dose Track
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Fish oil vs flaxseed: do they give the same omega-3s?

Omega-3 types · Conversion · Trials · Safety

Short answer: No. Fish oil supplies EPA and DHA directly; flaxseed supplies ALA, and the body turns less than 15% of ALA into EPA and DHA.1 Most heart research is on EPA and DHA.1 In one 12-week trial of 62 firefighters, fish oil quickly raised red blood cell DHA, while flax oil raised EPA but not DHA.2

How do fish oil and flaxseed compare side by side?

From the NIH Office of Dietary Supplements, NCCIH and a 2008 randomized trial.
Fish oilFlaxseed or flaxseed oil
Main omega-3sEPA and DHA1ALA13
Typical amountAbout 180 mg EPA and 120 mg DHA in a 1,000 mg capsule17.26 g ALA per tablespoon of flaxseed oil; 2.35 g per tablespoon of whole seeds1
Turned into EPA and DHAAlready EPA and DHA1Very limited: under 15%1
Daily intake set by NIH (adults)No intake set for EPA or DHA1ALA: 1.6 g men, 1.1 g women1
Key research2020 Cochrane review: triglycerides down about 15%; slight drop in heart deaths; no change in overall deaths or strokes1NIH lists small studies on weight and blood sugar; more research needed3
12-week trial (Barceló-Coblijn 2008)Rapid rise in red blood cell DHA22.4 or 3.6 g a day raised red blood cell ALA and EPA2
Side effectsFishy taste, bad breath, heartburn, nausea, diarrhea1Bloating, fullness, diarrhea at higher doses; do not eat raw or unripe seeds3
Blood thinnersMay prolong clotting with warfarin; 3 to 6 g a day mostly did not change it1Theoretical interaction with blood thinners3

Reviewed . Half-life figures are shown only where the value Dose Track uses agrees with the cited source.

Why does the type of omega-3 matter?

ALA, from flaxseed, soybean and canola oils, is the only omega-3 the body cannot make, which is why NIH sets intake levels for ALA. But the body converts very little of it, under 15%, into the longer EPA and DHA, so NIH says eating EPA and DHA directly is the only practical way to raise their levels.1

Most heart research has tested EPA and DHA from fish or fish oil rather than ALA from plants.1

Has flax oil been compared with fish oil?

Yes, in a 12-week randomized trial of 62 firefighters who took flax oil (1.2, 2.4 or 3.6 g a day), fish oil (0.6 or 1.2 g a day) or sunflower oil. Fish oil quickly raised red blood cell DHA. Flax oil at 2.4 g or more raised ALA and EPA, but the abstract does not report a DHA rise. Blood fats and inflammation markers did not differ between groups.2

What are the safety points?

  • Fish oil: FDA considers up to 5 g a day of EPA and DHA from supplements safe. Two large trials found 4 g a day for several years slightly raised the risk of atrial fibrillation in people with or at high risk of heart disease.1
  • Flaxseed: limited amounts may be safe up to 6 months. Some studies suggest it may be unsafe in pregnancy, though the evidence is not conclusive.3

If you take a blood thinner, ask your prescriber before either. More detail: Fish oil vs krill oil: which omega-3 source is absorbed better?, and the Omega-3 Fish Oil (EPA and DHA) and Flaxseed and Flaxseed Oil guides.

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Frequently asked questions

Is flaxseed oil a substitute for fish oil?+
Not directly. Flaxseed gives ALA; fish oil gives EPA and DHA. Under 15% of ALA becomes EPA and DHA in the body.1
Does flaxseed oil raise DHA?+
In a 12-week trial, flax oil raised red blood cell ALA and EPA, while fish oil raised DHA quickly.2
How much ALA do adults need?+
NIH lists an adequate intake of 1.6 g a day for men and 1.1 g for women. One tablespoon of flaxseed oil has 7.26 g.1
Does fish oil lower triglycerides?+
A 2020 Cochrane review cited by NIH found omega-3 supplements lowered triglycerides by about 15%.1
Can I track fish oil or flaxseed in Dose Track?+
Yes. Both are in the library; log each dose with reminders.

Sources

  1. NIH Office of Dietary Supplements. Omega-3 fatty acids fact sheet for health professionals (updated August 22, 2025).
  2. Barceló-Coblijn G, et al. Flaxseed oil and fish-oil capsule consumption alters human red blood cell n-3 fatty acid composition: a multiple-dosing trial comparing 2 sources of n-3 fatty acid. Am J Clin Nutr. 2008;88:801-809.
  3. NIH National Center for Complementary and Integrative Health. Flaxseed and flaxseed oil (updated February 2025).

All compound comparisons · Omega-3 Fish Oil (EPA and DHA) guide · Flaxseed and Flaxseed Oil guide · All compound guides · Peptide tracking in Dose Track