Fish oil

Short answer

Fish oil is an oil that contains the omega-3s EPA and DHA; omega-3 is the name of a group of fatty acids. According to NIH, a typical 1,000 mg fish oil capsule contains about 180 mg EPA and 120 mg DHA, but amounts vary widely between products; the Ministry of Health report likewise states that about 1 g of fish oil can contain 200 to 800 mg EPA+DHA. The forms (triglyceride, ethyl ester, re-esterified triglyceride, free fatty acid) differ in absorption, but all of them raise blood EPA and DHA levels. ^{[1] [6]}

Are fish oil and omega-3 the same thing?

No. Omega-3 is the general name for fatty acids such as ALA, EPA and DHA; fish oil, krill oil, cod liver oil and algal oil are supplement types that contain long-chain omega-3s (EPA and DHA). ^[1] EPA and DHA are not synthesized by the fish themselves but by microalgae at the base of the food chain; fish accumulate them through their diet. ^[1]

This difference matters when reading a label: “1,000 mg fish oil” on a capsule does not mean 1,000 mg of omega-3. According to NIH, a typical 1,000 mg of fish oil contains about 180 mg EPA and 120 mg DHA, and doses vary widely. ^[1] The Ministry of Health National Nutrition Council Fat Science Commission report also states that about 1 g of fish oil contains 200 to 800 mg EPA+DHA. ^[6]

The health effects of fish oil rest on the same body of evidence as the effects of EPA+DHA; that evidence is summarized in the main guide and on the benefits page.

Detailed guideWhat is omega-3? EPA, DHA, ALA, evidence and safety→ Detailed guideOmega-3 benefits: which claims are supported?→

Fish oil forms: triglyceride, ethyl ester, re-esterified

NIH states that omega-3s in supplements can be present in different forms such as natural triglyceride, free fatty acid, ethyl ester, re-esterified triglyceride and phospholipid. Natural triglycerides are the form found naturally in fish oil; ethyl esters are produced by replacing the glycerol in natural triglycerides with ethanol; re-esterified triglycerides are obtained by converting ethyl esters back into triglycerides. NIH’s summary: the bioavailability of the re-esterified triglyceride, natural triglyceride and free fatty acid forms is somewhat higher than that of ethyl ester, but all forms significantly raise plasma EPA and DHA levels. ^[1]

Two separate studies show this ranking with different numbers:

The two studies agree that ethyl ester is the least absorbed form; the order between triglyceride and free fatty acid differs between studies. In the Dyerberg study there was no difference between free fatty acid and natural triglyceride, whereas in Lawson and Hughes triglyceride was absorbed less than the free acid. The designs of the studies (duration, dose, fatty acid fraction measured, number of participants) differ widely, and the results cannot be directly converted to one another. Whether the absorption difference carries over to disease outcomes was not measured in these studies; NIH also notes that the reasons two 4 g/day studies, one with ethyl ester EPA and one with carboxylic acid EPA+DHA, gave different results are unclear. ^[1]

The dependence of absorption on the amount of fat in a meal is a separate topic and is covered on the timing page.

Detailed guideWhen to take omega-3? Meals, split doses and medication spacing→

Is krill oil superior to fish oil?

In krill oil the omega-3s are mostly in phospholipid form. According to NIH, some studies have shown these phospholipids to have slightly better bioavailability than the omega-3s in fish oil, while other studies have not. ^[1] Krill oil has not been shown to be superior to fish oil for clinical outcomes; the comparisons are based on blood fatty acid levels.

Algal oil: is there a plant-based DHA source?

Algae-derived omega-3 products generally provide about 100–300 mg DHA; some also contain EPA, and they are usually in triglyceride form. ^[1] In a randomized, open-label, parallel-group study of 32 healthy people aged 20–65, 600 mg/day of DHA from algal oil capsules or from weighed cooked salmon raised plasma phospholipid DHA by about 80% and erythrocyte DHA by about 25% after two weeks, with no difference between the two groups; the authors found the two sources bioequivalent. ^[4] The study is small, short (two weeks) and open-label; the measurement is blood DHA level, not a clinical outcome.

The Ministry of Health report states that the diets of vegetarians, especially vegans, contain fewer omega-3 fatty acids than those of non-vegetarians; fish-eating pesco-vegetarians differ in this respect. ^[6]

Why is cod liver oil evaluated separately?

According to NIH, cod liver oil supplements provide vitamins A and D in addition to long-chain omega-3s. ^[1] This means that when it is mistaken for “fish oil” and used for a different purpose, the vitamin intake must also be counted.

For the preformed (retinol) form of vitamin A, the tolerable upper intake level (UL) of the US Food and Nutrition Board is 3,000 µg RAE/day for ages 19 and over, including pregnancy and lactation, and 2,800 µg RAE for ages 14–18. This UL covers vitamin A from animal foods and from supplements consisting entirely of retinol or its esters. NIH also reports that experts recommend that people who are pregnant or may become pregnant, and those who are breastfeeding, not take high-dose vitamin A supplements (above 3,000 µg RAE [10,000 IU] per day), and that preformed vitamin A intakes above the UL can cause birth defects (malformations of the eyes, skull, lungs and heart). With long-term high intake, dry skin, muscle and joint pain, fatigue, depression and abnormal liver tests can occur. ^[7]

Therefore the amounts of vitamins A and D on a cod liver oil product label are added to total intake; in people who are pregnant or planning pregnancy, the choice of this product is made together with a physician. Details are on the vitamin A page.

What to look for on a fish oil label

• Total oil and EPA+DHA are separate numbers. The EPA and DHA amounts per serving are listed separately from the total oil in the capsule. ^[1]
• Form. Natural triglyceride, ethyl ester, re-esterified triglyceride and free fatty acid may be stated on the label; NIH emphasizes that formulations vary widely and labels should therefore be read, and reports that the NIH Dietary Supplement Label Database contains product labels. ^[1]
• Accompanying vitamins. Vitamins A and D in cod liver oil (above). ^[1]
• Freshness and oxidation. Below.

Oxidation and quality standards

Omega-3s are fatty acids highly susceptible to oxidation. The Ministry of Health report states that fish consumption is recommended over fish oil to avoid exposure to oxidized fatty acids, and reports excessive oxidation products in 11 to 62% of over-the-counter supplements sold in Norway, Poland, New Zealand and Brazil. ^[6]

In a study of 171 North American over-the-counter omega-3 products sold in Canada, 50% of the products exceeded the voluntary recommended levels for peroxide, anisidine and total oxidation (TOTOX) indicators; 18% were approaching the limits with 1–3 years left to expiration. The assessment used the standards of GOED (Global Organization for EPA and DHA Omega-3s) and IFOS (International Fish Oil Standards) and the voluntary limits of an industry association: peroxide 5 mEq/kg, anisidine 20 and TOTOX 26. In unflavored capsule products, secondary and total oxidation were significantly lower than in bulk oil and flavored products; in children’s products, primary, secondary and total oxidation were higher than in other products. ^[5] The study measured chemical oxidation indicators; it did not measure the consequences of these levels for human health. A shelf life of 3 years or longer means that oxidation can increase even while the product is within its expiration date. ^[5]

These standards are voluntary; this guide does not recommend brands or products and does not verify whether a product meets these standards.

Heavy metals

According to NIH, methylmercury is present in fish at varying levels; however, it has not been found in omega-3 supplements because it is removed during processing and purification. ^[1] The Ministry of Health report also states that fish should be free of heavy metals and of environmental contaminants such as dioxin and polychlorinated biphenyls (PCBs). ^[6] Mercury in fish as a food is covered separately on the foods page.

Detailed guideWhich foods contain omega-3? Serving table and fish of Türkiye→

What is the status of fish oil in Türkiye?

In Türkiye, most omega-3 products fall under the Turkish Food Codex Communiqué on Food Supplements (2013/49) of the Ministry of Food, Agriculture and Livestock, dated 16 August 2013 (Official Gazette No. 28737). The communiqué defines a food supplement as a product with a set daily intake dose, prepared in forms such as capsules, tablets or liquids from concentrates or extracts of nutrients such as vitamins, minerals, protein, carbohydrates, fiber, fatty acids and amino acids, to supplement normal nutrition. ^[8] This does not mean that the product’s efficacy has been proven; the evidence varies by area, as described on the benefits page.

This guide does not recommend personal doses or products. Fish oil use is evaluated with a physician, particularly in people taking anticoagulants, with a history of atrial fibrillation, or who are pregnant.