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In the krill oil vs fish oil debate, the honest answer is that both deliver the same two omega-3 fats, EPA and DHA, and neither has been shown to be clearly better for health. Krill oil carries its omega-3s mostly as phospholipids, while fish oil carries them mostly as triglycerides. Some studies suggest the phospholipid form is absorbed a little better; others find no real difference once the amounts are matched. Fish oil has far more research behind it, including large heart trials with mixed results. Krill oil usually contains less EPA and DHA per capsule, and because krill are crustaceans, it raises extra questions for people with shellfish allergy. Here is what the evidence says and how to compare labels.
Peptide Labs sells dietary supplements, but we do not sell fish oil or krill oil, so this comparison does not point you to any product. It is general information, not medical advice.
Key Takeaways
- Fish oil and krill oil both supply EPA and DHA; the main difference is the chemical form they come in.
- Absorption studies comparing the two are small and conflicting, and short-term differences may fade.
- Large trials of fish-derived omega-3 supplements found mixed results for heart outcomes.
- Prescription omega-3 drugs are a separate category with their own FDA-approved uses and warnings.
- Atrial fibrillation, bleeding questions with blood thinners and seafood allergy are the key safety points.
Krill oil vs fish oil: the main differences
| Feature | Fish oil | Krill oil |
|---|---|---|
| Source | Oily fish | Tiny ocean crustaceans called krill |
| Main omega-3 form | Triglycerides (or ethyl esters in some concentrates) | Mostly phospholipids |
| EPA and DHA per capsule | Usually higher, especially in concentrates | Usually lower |
| Extra compounds | None typical beyond the oil itself | Astaxanthin, the red pigment |
| Allergy question | Fish allergy | Shellfish allergy |
| Size of research base | Large, including multi-year trials | Small, mostly short studies |
Both oils get their omega-3s from the same place. According to the NIH Office of Dietary Supplements (ODS), EPA and DHA are made by microalgae at the base of the marine food chain, then build up in krill and fish. In the body they become part of the phospholipids that form cell membranes. Plant foods such as flaxseed supply a different omega-3, ALA, which the body converts to EPA and DHA only in small amounts.
Does krill oil absorb better than fish oil?
This is the main selling point for krill oil, and the evidence is genuinely split. ODS puts it plainly: some studies suggest the phospholipids in krill oil have somewhat higher bioavailability than the omega-3s in fish oil, and other studies do not. ODS also notes that all common forms, including triglycerides, ethyl esters and phospholipids, significantly raise blood EPA and DHA.
| Study | Design | Finding | Limits |
|---|---|---|---|
| Ulven, 2011 | 113 adults, krill oil, fish oil or nothing for 7 weeks | Blood EPA and DHA rose similarly with both oils, though krill supplied about two-thirds as much | Short; amounts not matched |
| Salem and Kuratko, 2014 | Reanalysis of krill studies | No evidence of better krill absorption | Authors worked for an omega-3 ingredient maker |
| Ulven and Holven, 2015 | Review of 14 papers | Krill may absorb better, but studies are hard to compare | Only two human studies matched amounts |
| Pham, 2024 | Network meta-analysis of 26 studies | Krill oil absorbed better at lower intakes | High heterogeneity; authors urge caution |
| Alijani, 2025 | Comprehensive review | Short-term differences often did not last in long-term studies | Oil blends vary, which muddies source comparisons |
Two points explain the confusion. First, krill oil has a lower concentration of EPA and DHA than fish oil, so trials often gave different amounts of each, which makes “same result from less oil” claims hard to judge. Second, a 2025 review found that faster absorption after a single serving often did not translate into higher omega-3 levels after weeks of regular use, and long-term levels are what matter for people taking a supplement every day. The fair summary is that any absorption edge for krill oil is small and unproven, and the total EPA and DHA you get matters more than the form.
Fish oil benefits: what large trials found
Most of what is known about fish oil benefits comes from trials of fish-derived omega-3 supplements. The results are mixed. In the VITAL trial, an omega-3 supplement did not significantly reduce the combined rate of heart attack, stroke and cardiovascular death over about five years, although total heart attacks were 28% lower. The ASCEND trial in people with diabetes also found no significant effect on serious vascular events. A 2019 meta-analysis of 13 trials with 127,477 participants concluded that marine omega-3 supplements lowered the risk of heart attack and coronary heart disease death.
The FDA allows a qualified health claim on foods and supplements with EPA and DHA: “Supportive but not conclusive research shows that consumption of EPA and DHA omega-3 fatty acids may reduce the risk of coronary heart disease.” The word “qualified” matters: it signals that the evidence is limited. The National Center for Complementary and Integrative Health adds that, for some conditions, the evidence for eating seafood is stronger than the evidence for supplements.
Prescription omega-3s are a different category
Some of the strongest omega-3 results come from prescription drugs, not supplements. In the REDUCE-IT trial of 8,179 people on statins, Vascepa (icosapent ethyl, a purified prescription form of EPA) cut cardiovascular events by 25% compared with a mineral oil placebo. The STRENGTH trial, which tested a different prescription EPA and DHA product in 13,078 people, found no significant benefit, and ODS notes that the reasons for the different results are not clear. Vascepa and Lovaza are FDA-approved for specific adults with high triglycerides, under a prescriber’s care. Their results cannot be transferred to over-the-counter fish oil or krill oil, which differ in form, purity and strength.
Krill oil benefits: what is actually known
Research on krill oil benefits is much thinner. Most studies measure blood omega-3 levels or blood lipids over a few weeks rather than health outcomes. In the 2011 Norwegian trial, neither krill oil nor fish oil changed blood lipids or markers of oxidative stress and inflammation compared with the control group, and the 2015 review found only limited effects of either oil on lipids and inflammatory markers. Krill oil also contains astaxanthin, the pigment that makes it red, but claims that this adds a health benefit have not been confirmed in large human trials. No multi-year outcome trial comparable to VITAL has tested krill oil supplements.
Side effects and safety for both oils
ODS and NCCIH describe the common side effects of omega-3 supplements as usually mild: an unpleasant taste, bad breath, heartburn, nausea, stomach discomfort, diarrhea, headache and odd-smelling sweat. The more serious questions are these:
- Atrial fibrillation: a 2021 meta-analysis of 7 trials with 81,210 participants linked marine omega-3 supplements to a 25% higher relative risk of atrial fibrillation, an irregular heart rhythm, and the risk was greater in trials using larger daily amounts. The Vascepa and Lovaza labels also carry atrial fibrillation warnings.
- Bleeding and blood thinners: ODS reports that most research finds no significant effect on warfarin control and a 2014 review found no rise in clinically significant bleeding, but fish oil may raise clotting-time results in some people. The Vascepa label reports more bleeding, especially with aspirin, clopidogrel or warfarin. Tell your prescriber before adding either oil.
- Shellfish allergy: krill are crustaceans, and in a laboratory study, antibodies from people with shrimp allergy reacted to krill protein. Ask an allergist before using krill oil if you have a shellfish allergy.
- Fish allergy: the prescription labels note it is not known whether people with fish or shellfish allergy react to fish-derived omega-3 products, and advise caution.
- Cod liver oil: it also supplies vitamins A and D, so count those if you take a multivitamin.
Pregnancy, breastfeeding, a heart rhythm condition, an upcoming surgery or a bleeding disorder are all reasons to check with your clinician first.
How to compare fish oil and krill oil labels
- Read EPA plus DHA, not total oil. A large softgel can hold mostly other fats. The Supplement Facts panel should list EPA and DHA separately.
- Check the form. Labels may say triglyceride, re-esterified triglyceride, ethyl ester or phospholipid. ODS notes that all of them raise blood omega-3 levels.
- Look for freshness and content testing. A 2015 study of all 32 fish oils sold in New Zealand found only 3 met their labeled EPA and DHA content and 83% exceeded a recommended oxidation limit. A 2017 retest by an omega-3 industry group found much better compliance, so results vary by market and method. Independent seals help; see our guide to third-party tested supplements.
- Note allergen statements and sources. Look for the species of fish or krill and the allergen statement, especially if you avoid seafood.
- Look at the whole formula. Many omega-3 products add vitamins or herbs. If a product also lists turmeric with black pepper, read our guide to turmeric and black pepper, because piperine can affect how some medicines are processed.
Frequently Asked Questions
Is krill oil better than fish oil?
Not clearly. Both supply EPA and DHA. Some studies suggest krill oil’s phospholipid form absorbs a little better, but others find no difference, and fish oil has far more long-term research.
What are the main fish oil benefits?
Large trials of fish-derived omega-3s found mixed results for heart outcomes, with fewer heart attacks in some analyses but no clear effect on combined events in others. FDA allows only a qualified claim.
What are the benefits of krill oil?
Krill oil raises blood EPA and DHA like fish oil does. Claims beyond that, including for astaxanthin, have not been confirmed in large human outcome trials.
Can I take krill oil if I am allergic to shellfish?
Ask an allergist first. Krill are crustaceans, and a lab study found that antibodies from people with shrimp allergy reacted to krill protein.
Do omega-3 supplements affect heart rhythm?
Pooled trials linked omega-3 supplements to a higher risk of atrial fibrillation, especially at larger daily amounts. Talk with your clinician if you have a heart rhythm condition.
Is prescription fish oil the same as a supplement?
No. Vascepa and Lovaza are FDA-approved drugs with defined uses, purity standards and warnings. Their trial results do not apply to over-the-counter products.
Questions about a label? Contact us or read our Buyer’s Guide. Follow the label and ask a healthcare provider before starting any supplement, especially if you take medicines. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
Last reviewed October 2026.
Related guides: Third Party Tested Supplements: What USP, NSF and Other Seals Mean, Turmeric and Black Pepper: Why Piperine Is Added and What to Know, How to Boost Metabolism: What Really Changes the Calories You Burn, Astaxanthin: Benefits, Side Effects and What the Research Shows, Nattokinase: Benefits, Side Effects and Bleeding Risks.