Composition

Fish Oil Composition

Fish oil is not a single chemical substance. It is a complex mixture of fats whose exact composition depends on the species of fish, diet, season, environment, part of the fish used and the way the oil is processed.

Triglycerides and Fatty Acids

Most of the fat in natural fish oil is present as triglycerides. A triglyceride consists of a glycerol molecule attached to three fatty acids, and the particular fatty acids attached to it determine many of the oil’s nutritional and physical properties.

Fish oils contain a mixture of saturated, monounsaturated and polyunsaturated fatty acids. Their best-known components are the long-chain omega-3 fatty acids EPA and DHA.

EPA

EPA, or eicosapentaenoic acid, is a long-chain omega-3 fatty acid containing 20 carbon atoms and five double bonds. It participates in the production of signaling molecules involved in inflammatory and cardiovascular processes.

DHA

DHA, or docosahexaenoic acid, contains 22 carbon atoms and six double bonds. It is an important structural fatty acid in cell membranes and is particularly concentrated in the brain and retina.

EPA and DHA Levels Vary

There is no universal EPA-to-DHA ratio for fish oil. Different fish species naturally contain different fatty-acid profiles, and commercial supplements may also be concentrated or processed to provide particular amounts of EPA and DHA.

For this reason, “1,000 mg fish oil” does not necessarily mean 1,000 mg of omega-3 fatty acids. A typical 1,000 mg fish oil capsule may contain only a fraction of that amount as EPA and DHA, while concentrated products can contain much more.

When comparing supplements, the quantities of EPA and DHA listed on the label are more informative than the total amount of fish oil.

Other Components of Fish Oil

Depending on its source and processing, fish oil can also contain smaller quantities of other fatty acids, phospholipids, sterols and naturally occurring lipid-soluble compounds.

Cod liver oil is compositionally distinct because it naturally provides vitamins A and D in addition to EPA and DHA.

Different Forms of Omega-3 Supplements

Omega-3s in supplements can occur in several chemical forms. These include natural triglycerides, re-esterified triglycerides, ethyl esters, free fatty acids and phospholipids.

These forms differ somewhat in digestion and absorption, although each can increase EPA and DHA levels when consumed appropriately. The overall dose, product quality and consistency of use are generally more useful information for consumers than simply labeling one chemical form as universally superior.

More detailed information about the composition and forms of omega-3 supplements is available from the NIH Office of Dietary Supplements.