Fish Oil vs Krill Oil: Does the Form Change the Outcome

What differs between the two oils

Most of the EPA and DHA in fish oil sits on a glycerol backbone as triglycerides, although concentrates are sold as ethyl esters too. Krill oil comes from Euphausia superba, a small Antarctic crustacean, and much of its omega-3 is bound to phospholipids instead. Köhler and colleagues put that share at 30 to 65 percent of the EPA and DHA in krill, with fish carrying almost all of theirs as triglycerides.

The reasoning behind the claim is sound. Phospholipids are amphiphilic, so they may emulsify fat in the gut more easily. A plausible mechanism isn't a trial result though.

Counting what's in the softgel

The dose difference is the largest part of the comparison.

Ulven and colleagues randomized 113 adults with normal or slightly elevated cholesterol or triglycerides to 3.0 g/day of krill oil (543 mg EPA + DHA), 1.8 g/day of fish oil (864 mg EPA + DHA), or nothing. Both supplemented groups increased plasma EPA, DHA, and docosapentaenoic acid against the controls, and the two oils didn't differ significantly in any omega-3 measured, in serum lipids, or in markers of oxidative stress and inflammation.

The arithmetic is unfriendly to a straight swap. Trading fish oil for krill oil capsule for capsule usually cuts your EPA and DHA intake substantially.

Where the absorption claim comes from

The trial most often cited is small.

Ramprasath and colleagues put 24 healthy volunteers through a double-blind crossover in which each 4-week phase supplied a matched 600 mg of EPA + DHA per day from krill oil or fish oil, with corn oil control and 8-week washouts. Both marine oils raised plasma and red blood cell omega-3 against placebo. The omega-3 index, the sum of EPA and DHA in red blood cell membranes, rose about twice as much after krill oil (p = 0.0143). Two of the authors worked for a krill oil manufacturer.

Salem and Kuratko reviewed that literature in 2014 and rejected the conclusion on arithmetic grounds. When a slightly lower dose produces the same blood level, the dose gap was too small to have shown a difference anyway, so a tie proves nothing superior. Both of those authors worked for DSM Nutritional Products, which sells fish oil ingredients. This question has industry money on both sides.

The dose-matched trials disagree

Yurko-Mauro and colleagues set out to fix precisely that flaw. Sixty-six healthy adults, 22 per arm, took 1.3 g/day of EPA + DHA for 28 days regardless of form, as fish oil ethyl esters, fish oil triglycerides, or krill oil.

At week 4, plasma EPA + DHA reached 90.9 ± 41 µg/mL with ethyl esters and 118.5 ± 48 µg/mL with krill oil, triglycerides sitting at 108 ± 40 µg/mL, overall p = 0.052. Red blood cell EPA + DHA wasn't significantly different across the three (p = 0.19). Several authors were DSM employees.

The most recent trial ran longer. Seventy-two healthy adults took 1.1 g/day of EPA + DHA for 12 weeks as krill oil or fish oil. The rise in plasma EPA was roughly 1.5 times larger with krill oil (p = 0.0001), and DHA moved the same way (p = 0.005). Funding came from the Canadian Institutes of Health Research, with capsules supplied in kind by producers of both oils.

Both designs are reasonable, and the results don't reconcile.

One trial that splits phospholipids from food matrix

Köhler's group added a comparison the other trials skipped.

Fifteen subjects took single doses of krill oil, krill meal, and fish oil each supplying about 1,700 mg of EPA and DHA, tracked over 72 hours. The incremental area under the curve for EPA and DHA came out at 89.08 ± 33.36% × h after krill oil against 59.15 ± 22.22% × h after fish oil (p = 0.003).

The third arm matters most. Krill meal produced 44.97 ± 18.07% × h, no better than fish oil, despite its omega-3 also being mostly bound to phospholipids. If phospholipids were doing the work, krill meal should have landed near krill oil. The authors read that as evidence against the phospholipid explanation and pointed at food matrix differences instead. A krill producer sponsored it, and it ran in fifteen people.

Why a blood marker isn't an outcome

This is where marketing and evidence part company.

Every trial above measured something in blood or red blood cells. None measured heart attacks, stroke, cognitive change, joint symptoms, or mortality. The 2026 trial is the cleanest dose-matched comparison available, and it assessed plasma concentrations only.

The omega-3 index has observational work behind it linking higher values to lower cardiovascular risk, so it isn't a meaningless number. A surrogate marker is still a surrogate marker, and no manufacturer has run the years-long trial that would turn a bigger rise in red blood cell EPA into a demonstrated benefit. Fish oil carries its own tangled record on hard endpoints, with large trials disagreeing with each other.

Oxidation, and why product testing varies

One measured difference does lean toward krill oil, and it isn't about absorption. In an analysis of the 48 top-selling US omega-3 supplements, krill oil showed comparatively low peroxide values, consistent with higher oxidative stability reported for phospholipid-rich oils. GOED, the omega-3 trade association, led that work with member laboratories, so adjust expectations accordingly.

The wider picture is messier. Jackowski and colleagues analyzed 171 omega-3 supplements sold in Canada and reported that about half exceeded voluntary limits for markers of oxidation, with another 18 percent approaching them. Marked inter-laboratory variability showed up in the US analysis too. Both surveys point at product age and storage more than at the species on the label.

Frequently asked questions

Does the phospholipid form mean I need a smaller dose?

The record doesn't establish that. At 1.3 g/day matched in 2015, both forms produced comparable blood levels. The 2026 trial found larger increases with krill oil at 1.1 g/day, so it depends on which of two small trials persuades you.

Is krill oil better for triglycerides or cholesterol?

Nothing in the head-to-head record supports that. Ulven's group found no significant difference in serum lipids over 7 weeks, and none of these trials was powered on a lipid endpoint.

Are the krill trials independent of the industry?

Mostly not, and it runs both ways. Suppliers employed authors on trials from 2009 and 2015, a krill producer sponsored the crossover work, and even the publicly funded 2026 trial had capsules donated by producers of both oils.

Can this page tell me which one to take?

No. That depends on your blood values, your medications, your diet, and your reasons for asking. What can be said is that the strongest label claim rests on two small conflicting trials measuring a surrogate marker.

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This article is for general information only and does not constitute medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration and are not intended to diagnose, treat, cure, or prevent any disease. Talk with your health care provider before using omega-3 supplements, especially if you take prescription medication.

Sources

• Ulven et al., Metabolic effects of krill oil versus fish oil, Lipids 2011
• Yurko-Mauro et al., Similar EPA and DHA plasma levels with fish oil or krill oil, Lipids Health Dis 2015
• Salem and Kuratko, A reexamination of krill oil bioavailability studies, Lipids Health Dis 2014
• Köhler et al., Bioavailability of fatty acids from krill oil, krill meal and fish oil, Lipids Health Dis 2015
• Loukil et al., Krill oil raises plasma omega-3 more than fish oil, Am J Clin Nutr 2026
• Jackowski et al., Oxidation levels of North American n-3 supplements, J Nutr Sci 2015

Maki et al., Krill oil supplementation and plasma EPA and DHA in overweight adults, Nutr Res 2009, PMID 19854375. Bannenberg et al., Label claim compliance and oxidative quality of EPA/DHA retail products in the U.S., J Food Compos Anal 2020.