Health Reference Library

Omega 3 vs fish oil: what is the difference?

This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.

Summary

Omega 3 is the family of fats your body needs; fish oil is the most common way to get two of them, EPA and DHA. So the question is really which source and how much EPA and DHA it delivers. A capsule labelled 1000 mg fish oil might hold only 300 mg of omega 3, while a concentrated capsule of the same size can hold 550 mg. The plant form, ALA in flax and chia, converts to EPA and DHA poorly, which is why fish, krill or algal oil are the sources that move blood levels. Read the EPA and DHA figures, not the oil weight; the NHS advice is oily fish once a week first.

How it works

EPA and DHA are built into cell membranes, where they change how flexible the membrane is and which signalling molecules the cell makes. EPA is the one the large cardiovascular trials used at high dose; DHA is the main omega 3 in the brain and retina. The omega 3 index, the share of EPA and DHA in red cell membranes, is the measure that tracks intake, and it takes three to four months of steady dosing to rise to a new plateau. The form of the oil matters less than the dose taken consistently with a meal containing fat.

Effective dose

The NHS advice is two portions of fish a week, one of them oily, and there is no UK reference intake for EPA and DHA from supplements. Most trials of general health outcomes used 250 to 1000 mg of EPA plus DHA a day. The large cardiovascular trials are the exception: REDUCE-IT used 4 g a day of purified EPA in people with high triglycerides already on other care, and the STRENGTH trial at a similar dose of a mixed oil found no benefit, so those results do not transfer to ordinary supplements. For the omega 3 index, 1000 to 2000 mg of EPA plus DHA a day is what moved most people from a low reading to the target range over four months.

Forms compared

Three omega 3 fats matter. ALA is the plant one, in flaxseed, chia and walnuts; the body converts only a few percent of it into EPA and DHA. EPA and DHA are the marine ones, made by algae and concentrated up the food chain into oily fish. Fish oil is simply the oil from those fish, and its EPA and DHA content varies with the species and with how far the manufacturer has concentrated it. Standard fish oil is about 30 percent omega 3. Concentrated oils, usually in ethyl ester or re-esterified triglyceride form, reach 50 to 90 percent. Krill oil carries its EPA and DHA on phospholipids and adds astaxanthin, at a lower dose per capsule. Algal oil gives DHA, and sometimes EPA, with no fish at all.

Timing

Take it with the meal that contains the most fat, usually lunch or dinner. Absorption of ethyl ester oils roughly doubles with a fatty meal. Fishy aftertaste is reduced by taking the capsule at the start of the meal or keeping the bottle in the fridge.

Safety profile

The European Food Safety Authority found supplemental EPA plus DHA up to 5 g a day raises no safety concern for adults, and US regulators use 3 g a day as their line. At high doses bleeding time can lengthen; anyone with a clotting disorder, or with surgery planned, should ask their GP before taking omega 3 at high doses. Fish oil is not suitable for people with fish allergy; algal oil is. Pregnant women should choose an oil rather than fish liver oil, which carries vitamin A.

Guideline positions

NHS Live Well: fish and shellfish, two portions a week, one oily. NICE NG238 (2023): omega 3 supplements are not recommended for cardiovascular risk reduction. REDUCE-IT (2019) and STRENGTH (2020), the two large high dose trials with opposite results. VITAL (2019): 1 g a day of fish oil did not reduce major cardiovascular events in a general population.

Practical framework

Decide the dose of EPA plus DHA first, then choose the oil that gets you there in the fewest capsules. Nutri Tailor stocks [Omega 3 capsules](/products/omega-3), 1000 mg of concentrated fish oil giving 330 mg EPA and 220 mg DHA per capsule from anchovy, sardine and mackerel, and [Krill Oil](/products/krill-oil), 500 mg giving 68 mg EPA and 30 mg DHA on phospholipids with astaxanthin, for people who prefer a small capsule. If you want to know whether your dose is working, the omega 3 index is the test. This is a summary of published research, not personal health advice. Talk to your GP or a registered nutritional therapist before changing what you take, especially if you are pregnant, have a diagnosed condition or are under ongoing care.

Common misconceptions

That 1000 mg of fish oil means 1000 mg of omega 3: it usually means about 300 mg. That flaxseed oil is a substitute: it supplies ALA, which converts poorly. That krill oil is many times better absorbed: the phospholipid form is absorbed well, but at a much smaller dose per capsule, so you need more capsules for the same EPA and DHA. That omega 3 supplements protect the heart: the NICE guideline says not for the general population.

Forms compared

Omega 3Fish Oil

Sources

  1. UK NHS. Fish and shellfish — NHS Live Well. NHS UK (UK government).
  2. NICE (UK government) 2023. Cardiovascular disease: risk assessment and reduction, including lipid modification. National Institute for Health and Care Excellence (NICE).
  3. Bhatt DL, Steg PG, Miller M, Brinton EA, Jacobson TA, Ketchum SB, Doyle RT, Juliano RA, Jiao L, Granowitz C, Tardif JC, Ballantyne CM 2019. Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia (REDUCE-IT). New England Journal of Medicine. PMID: 30415628 · DOI: 10.1056/nejmoa1812792
  4. Nicholls SJ, Lincoff AM, Garcia M, Bash D, Ballantyne CM, Barter PJ, Davidson MH, Kastelein JJP, Koenig W, McGuire DK, Mozaffarian D, Ridker PM, Ray KK, Katona BG, Himmelmann A, Loss LE, Rensfeldt M, Lundström T, Agrawal R, Menon V, Wolski K, Nissen SE 2020. Effect of High-Dose Omega-3 Fatty Acids vs Corn Oil on Major Adverse Cardiovascular Events in Patients at High Cardiovascular Risk: The STRENGTH Randomized Clinical Trial. JAMA. PMID: 33190147 · DOI: 10.1001/jama.2020.22258
  5. Manson JE, Cook NR, Lee IM, Christen W, Bassuk SS, Mora S, Gibson H, Albert CM, Gordon D, Copeland T, D'Agostino D, Friedenberg G, Ridge C, Bubes V, Giovannucci EL, Willett WC, Buring JE 2019. Marine n-3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer (VITAL). New England Journal of Medicine. PMID: 30415637 · DOI: 10.1056/nejmoa1811403

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