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Krill Oil vs Fish Oil - What's the difference between them?

Medically reviewed by Last updated on April 3, 2023.

Official answer


The differences between krill and fish oil are:

  • Krill oil is inherently more stable than fish oil, and lacks a fishy smell and taste.
  • Krill oil appears to be better absorbed than fish oil, but more studies are needed to determine whether this translates into any further health benefits.

Both fish oil and krill oil are a source of omega-3 fatty acids, predominantly EPA and DHA.

Harvesting of both fish and krill for their respective oils has an impact on our environment, and most human studies have failed to show significant health benefits.

The best way to improve your omega-3 intake is to eat fish at least twice a week, as recommended by the American Heart Association (who notably prefer increasing dietary intake of fish over supplements).1

Where do companies source fish oil and krill oil from?

Fish oil is derived from the tissues of cold-water oily fish, most notably salmon, herring, mackerel, anchovies, and sardines. Some companies, but not all, do this using sustainable fish-farming practices.2,3

Concerns about accumulation of toxins, such as mercury, dioxins, and polychlorinated biphenyls (PCBs), as well as stability and taste problems with fish oils and the ongoing decline in the world’s fish populations prompted the search for alternative sources of omega-3 fatty acids. One of these is krill oil.3,4

Krill oil is extracted mainly from Antarctic krill – a small shrimp-like crustacean – and is sourced directly from the open ocean feeding grounds. Although Krill congregate at certain times of year in swarms so dense they can be seen from space, recent studies suggest Antarctic krill stocks have fallen by 80% since the 1970s.4 Krill represent a massive link in the global food chain, being the main staple in the diets of hundreds of different animals, including fish, birds, and whales. Harvesting of Krill oil is not without controversy because, as the fuel of the Earth’s marine ecosystem, any decline in their numbers is a serious cause for concern.4,5

What are omega-3 fatty acids?

Omega-3 fatty acids are a type of unsaturated fatty acid that are vital for brain and nerve function. They are called an “essential fatty acid” because we cannot manufacture them ourselves and must get them from food.6

There are three main types of omega-3 fatty acids:

  • eicosapentaenoic acid (EPA)
  • docosahexaenoic acid (DHA)
  • alpha-linolenic acid (ALA).

EPA and DHA are synthesised by algae and marine plants, particularly in cold water. As a result, most marine-based supplements, including fish oil and krill oil, contain EPA and DHA.6

ALA is made by plants and high amounts of ALA can be found in vegetable oils and nuts. Flax seeds, canola, soy, perilla, and walnuts are all high in ALA. In addition, ALA is also found in the fat of animals that eat grass. Our bodies are able to convert ALA into EPA and DHA; however, research suggests less than 1% ALA is converted.6,7

Do fish oil and krill oil contain the same amounts of EPA and DHA and is there any difference in stability or absorption?

The EPA and DHA in fish is mostly contained as triglycerides at a ratio of 1:1.8 Fish oils in general are inherently unstable and highly susceptible to oxidation which degrades the quality of the oil. Even with the addition of antioxidants, such as vitamin C or E, it can be a challenge for manufacturers of fish oil supplements to maintain quality during the shelf-life of a product and several studies have indicated that not all succeed.9 Oxidized fish oils could theoretically have the opposite effect of what they are intended for – some experts have suggested they may increase inflammation rather than decrease it – although studies so far have not proved this. Fish oils also tend to have a fishy smell, and most contain flavorings to mask this unpleasant scent, although these may also hide signs of possible rancidity.2,8,9

Krill oil contains EPA and DHA at a ratio of 2:1 and 30-65% of the omega-3 content is found in the form of phospholipids.8 Potentially, this gives krill oil some absorption advantages over fish oil because phospholipids make up the structure of cell membranes; therefore, passage of the omega-3’s in krill oil through the intestinal wall and into the blood stream should be easier. At least two good quality studies support this theory.8,9 In addition, krill oil naturally contains at least two known antioxidant compounds (astaxanthin and tocopherol [a form of vitamin E]) and possibly other compounds that help protect against rancidity with time, making it much more stable than fish oil. Because it is not extracted from fish, there is no fishy smell or after taste.3,8,9

Are there any studies that compare Fish oil to Krill oil?

Few studies have compared fish oil to krill oil and a review noted it was difficult to draw any firm conclusions from their results, since the majority used differing doses of EPA and DHA.8 Many studies also only investigated resultant levels of EPA and DHA in the body, rather than actual health effects. Of those that did, only one study reported a decrease in total cholesterol with both fish oil and krill oil; other studies showed no effects on lipids, and one even showed an increase in total cholesterol and LDL cholesterol with krill oil. Another study measured oxidative stress and inflammatory markers, and noted no difference. More studies are needed to investigate and additional potential health benefits of krill oil over fish oil or increased dietary fish intake.8

What evidence is there for the beneficial effects of omega-3 supplements in general?

Although experts agree food sources rich in omega-3s are vital to maintain healthy body function, few studies have confirmed any benefits for additional dietary intake or supplementation.

A Cochrane review stated it was unclear whether omega-3 fatty acids (taken as food or as a supplement) changed the risk of death, heart attack, stroke, or cancer in people with or without pre-existing cardiovascular disease.10

No convincing evidence was found for omega-3 supplementation in the prevention of cognitive decline and the treatment of mild to moderate Alzheimer’s Disease.11,12

In intermittent claudication (symptoms include a tired, aching, crampy-type leg pain sometimes associated with burning that typically occurs with walking) a Cochrane review found no evidence of a consistent benefit for omega-3 fatty acids. Supplements were also more likely to cause diarrhea, nausea, or flatulence.13

For cystic fibrosis, supplements may provide some benefits; however, the results were not significant enough to recommend routine supplementation.14

For type-2 diabetes, no effect on blood glucose control or fasting insulin was noted for omega-3 fatty acid supplementation, although some triglyceride lowering was noted (however, there was a trend towards an increase in LDL cholesterol).15

For many other disorders such as ADHD, bipolar, Crohn’s disease or Multiple Sclerosis there appears to be little benefit for omega-3 supplementation.16,17,18,19

Does fish oil have more side effects than krill oil?

Many fish oil supplements have a fishy odor or taste, although this may be reduced by encapsulation or added flavorings. Any pungent odor, gel discoloration or very unpalatable taste likely indicates excessive oxidation of the supplement and it should be thrown away or returned to the store if recently brought. Only small quantities of supplements should be brought at one time and they should be kept in an airtight container and refrigerated once opened, unless stated otherwise on the packaging.2,9

Theoretically, people who are allergic to fish or shellfish should avoid fish oil or krill oil supplements. However, there has only been one documented case of an anaphylactic reaction to fish oil and none to krill oil, indicating that an allergy to supplements is extremely rare. Always speak to your doctor before taking supplements if you have a fish or shellfish allergy.20

In general, omega-3 supplements (includes both fish and krill oil) may affect blood sugar levels, lower blood pressure, and increase the risk of bleeding, particularly at higher dosages or in those with bleeding disorders or already taking medications that increase the risk of bleeding (such as warfarin or aspirin). Higher dosages of fish oil may also lead to vitamin A or D toxicity. Cough, diarrhoea, nausea, and flatulence are common side effects associated with their use.2,5

For a full list of side effects see the fish oil or krill oil side effects pages.2,5

Always talk to your doctor before taking supplements of any kind, including omega-3’s, and particularly if you have a medical condition such as asthma, inflammatory bowel disease, liver disease or a heart rhythm disorder. Take a supplement from a reputable manufacturer with good quality control measures to ensure the supplement is as free from contaminants, including heavy metal toxins (such as mercury), as possible. Pregnant women and young children should be especially cautious about taking fish oil supplements.

  1. Fish and Omega-3 Fatty Acids. American Heart Association 06/2015
  2. Fish oil.
  3. Ulven SM, Holven KB. Comparison of bioavailability of krill oil versus fish oil and health effect. Vascular Health and Risk Management. 2015;11:511-524. doi:10.2147/VHRM.S85165.
  4. Questioning Krill Harvesting: Why Krill Oil Isn't an Eco-Friendly or Sustainable Source of Marine Omega-3 Oils Fen 2009.
  5. Krill oil
  6. Omega 3 fatty acids. University of Maryland Medical Center. Reviewed 05/2015
  7. Alpha-linolenic acid. University of Maryland Medical Center Reviewed 06/2014
  8. Engström K, Saldeen A-S, Yang B, Mehta JL, Saldeen T. Effect of fish oils containing different amounts of EPA, DHA, and antioxidants on plasma and brain fatty acids and brain nitric oxide synthase activity in rats. Upsala Journal of Medical Sciences. 2009;114(4):206-213. doi:10.3109/03009730903268958.
  9. Jackowski SA, Alvi AZ, Mirajkar A, et al. Oxidation levels of North American over-the-counter n-3 (omega-3) supplements and the influence of supplement formulation and delivery form on evaluating oxidative safety. Journal of Nutritional Science. 2015;4:e30. doi:10.1017/jns.2015.21.
  10. Hooper L, Harrison RA, Summerbell CD, Moore H, Worthington HV, Ness A, Capps N, Davey Smith G, Riemersma R, Ebrahim S. Omega 3 fatty acids for prevention and treatment of cardiovascular disease. Cochrane Database of Systematic Reviews 2004, Issue 4. Art. No.: CD003177. DOI: 10.1002/14651858.CD003177.pub2.
  11. Burckhardt M, Herke M, Wustmann T, Watzke S, Langer G, Fink A. Omega-3 fatty acids for the treatment of dementia. Cochrane Database of Systematic Reviews 2016, Issue 4. Art. No.: CD009002. DOI: 10.1002/14651858.CD009002.pub3.
  12. Sydenham E, Dangour AD, Lim WS. Omega 3 fatty acid for the prevention of cognitive decline and dementia. Cochrane Database of Systematic Reviews 2012, Issue 6. Art. No.: CD005379. DOI: 10.1002/14651858.CD005379.pub3.
  13. Campbell A, Price J, Hiatt WR. Omega-3 fatty acids for intermittent claudication. Cochrane Database of Systematic Reviews 2013, Issue 7. Art. No.: CD003833. DOI: 10.1002/14651858.CD003833.pub4.
  14. Oliver C, Watson H. Omega-3 fatty acids for cystic fibrosis. Cochrane Database of Systematic Reviews 2016, Issue 1. Art. No.: CD002201. DOI: 10.1002/14651858.CD002201.pub5.
  15. Hartweg J, Perera R, Montori VM, Dinneen SF, Neil AHAWN, Farmer AJ. Omega-3 polyunsaturated fatty acids (PUFA) for type 2 diabetes mellitus. Cochrane Database of Systematic Reviews 2008, Issue 1. Art. No.: CD003205. DOI: 10.1002/14651858.CD003205.pub2.
  16. Gillies D, Sinn JKH, Lad SS, Leach MJ, Ross MJ. Polyunsaturated fatty acids (PUFA) for attention deficit hyperactivity disorder (ADHD) in children and adolescents. Cochrane Database of Systematic Reviews 2012, Issue 7. Art. No.: CD007986. DOI: 10.1002/14651858.CD007986.pub2.
  17. Montgomery P, Richardson AJ. Omega-3 fatty acids for bipolar disorder. Cochrane Database of Systematic Reviews 2008, Issue 2. Art. No.: CD005169. DOI: 10.1002/14651858.CD005169.pub2.
  18. Lev-Tzion R, Griffiths AM, Ledder O, Turner D. Omega 3 fatty acids (fish oil) for maintenance of remission in Crohn's disease. Cochrane Database of Systematic Reviews 2014, Issue 2. Art. No.: CD006320. DOI: 10.1002/14651858.CD006320.pub4.
  19. Farinotti M, Vacchi L, Simi S, Di Pietrantonj C, Brait L, Filippini G. Dietary interventions for multiple sclerosis. Cochrane Database of Systematic Reviews 2012, Issue 12. Art. No.: CD004192. DOI: 10.1002/14651858.CD004192.pub3.
  20. Anaphylaxis to krill oil or fish oil: A risk for patient’s sensitive to shellfish or fish? 10/2013 American Academy of Asthma, Allergy or Immunology.

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