Fish Oil vs Krill Oil: Omega-3 Form and Absorption
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Fish oil vs krill oil: which omega-3 source is absorbed better?

Omega-3 form · Absorption studies · Safety · Allergies

Short answer: Both supply the omega-3s EPA and DHA. In krill oil they are mostly bound to phospholipids; NIH says some studies suggest this is absorbed somewhat better than fish oil and others do not.1 In a 4-week trial that matched the EPA and DHA dose, blood levels were not significantly different.2 Neither is approved by FDA before sale.3

How do fish oil and krill oil compare side by side?

From the NIH Office of Dietary Supplements, FDA and published head-to-head studies.
Fish oilKrill oil
Omega-3 formNatural triglycerides; some products use ethyl esters or re-esterified triglycerides1Mostly phospholipids1
Typical contentAbout 180 mg EPA and 120 mg DHA per 1,000 mg of fish oil, though products vary widely1Check the label for EPA and DHA per serving
Absorption, dose-matched (4 weeks)Plasma EPA + DHA 90.9 µg/mL (ethyl ester) and 108 µg/mL (triglyceride)2118.5 µg/mL; differences not significant2
Absorption, unmatched (7 weeks)864 mg EPA + DHA a day4543 mg EPA + DHA a day; similar rise in blood omega-3s4
Safety limitFDA: up to 5 g a day of EPA + DHA from supplements is safe as recommended1Same EPA + DHA limit applies1
Allergy noteFish is a major food allergen5Krill are crustaceans; crustacean shellfish is a major food allergen5
FDA approvalSupplements are not approved by FDA before sale3Same3

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

What did head-to-head studies find?

  • Yurko-Mauro 2015: 66 healthy adults took 1.3 g a day of EPA + DHA for 28 days as fish oil ethyl esters, fish oil triglycerides or krill oil, with the same EPA and DHA in each. Plasma EPA + DHA at week 4 was 90.9, 108 and 118.5 µg/mL, not significantly different (p = 0.052); red blood cell levels were also similar.2
  • Ulven 2011: 113 adults took krill oil (3.0 g a day, 543 mg EPA + DHA), fish oil (1.8 g a day, 864 mg EPA + DHA) or nothing for 7 weeks. Blood omega-3s rose similarly with both oils, and blood fats and markers of inflammation did not differ between groups.4

The NIH fact sheet sums up the wider literature: some studies suggest krill phospholipids are absorbed somewhat better, and others do not.1

What safety notes apply to both?

NIH lists usually mild side effects for omega-3 supplements: unpleasant taste, bad breath, heartburn, nausea, stomach upset, diarrhea, headache and smelly sweat. High doses might raise bleeding time; fish oil might raise INR with warfarin, though most research found 3 to 6 g a day of fish oil did not significantly change anticoagulation.1

More detail: the Omega-3 Fish Oil (EPA and DHA) and Krill Oil guides.

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Frequently asked questions

Is krill oil absorbed better than fish oil?+
Not clearly. NIH says some studies suggest it is and others do not. In a 4-week study that matched the EPA and DHA dose, blood levels were not significantly different.12
Does krill oil work at a lower dose?+
In one 7-week study, krill oil with 543 mg EPA + DHA a day raised blood omega-3s about as much as fish oil with 864 mg a day.4 A later dose-matched study found no significant difference.2
Can I take krill oil with a shellfish allergy?+
Ask your clinician first. Krill are crustaceans, and FDA lists crustacean shellfish as a major food allergen.5
How much EPA and DHA is safe?+
NIH reports that FDA has concluded supplements providing no more than 5 g a day of EPA and DHA combined are safe when used as recommended.1
Can I track fish oil or krill oil in Dose Track?+
Yes. Log each capsule or serving with reminders alongside your other medicines.

Sources

  1. NIH Office of Dietary Supplements. Omega-3 fatty acids fact sheet for health professionals (updated August 22, 2025).
  2. Yurko-Mauro K, et al. Similar eicosapentaenoic acid and docosahexaenoic acid plasma levels achieved with fish oil or krill oil in a randomized double-blind four-week bioavailability study. Lipids Health Dis. 2015;14:99.
  3. FDA. Questions and answers on dietary supplements.
  4. Ulven SM, et al. Metabolic effects of krill oil are essentially similar to those of fish oil but at lower dose of EPA and DHA, in healthy volunteers. Lipids. 2011;46:37-46.
  5. FDA. Food allergies: what you need to know.

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