Fish Oils

Medically reviewed on June 7, 2018

What is Fish Oils?

Fish oils are mostly comprised of the omega-3 fatty acids EPA and DHA; "fish oil" is a term frequently used interchangeably with EPA and DHA. Marine sources containing the highest content of omega-3 fatty acids are fatty fish (eg, mackerel, halibut, salmon, bluefish, mullet, sablefish, menhaden, anchovy, herring, lake trout, coho, sardines), which provide 1 g or more of omega fatty acids per serving of fish. Tuna, seal, and shellfish (eg, oysters) are additional sources.

Because marine fish stocks are limited and because many fish stocks are currently contaminated by pollutants (eg, methylmercury, organochlorine pesticides), it has been proposed that the algal genes, which produce EPA and DHA production be cloned into plants. Oils from transgenic plants would be rich in EPA and DHA, and although some success has been achieved, adapting algal genes to work in higher plants has not yet proven commercially viable. EPA and DHA can be transformed in the body, albeit inefficiently, from the essential omega-3 fatty acid alpha-linolenic acid (ALA), but ALA cannot be synthesized by humans and must be obtained from the diet. ALA is found in flaxseed, canola, soybean, walnut, and wheat germ oils, nuts and seeds, and vegetables. Additionally, EPA can be transformed into DHA in the body.

Scientific Name(s)

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)

Common Name(s)

Marine oils, marine oil fatty acids, n-3 fatty acids, omega-3 fatty acids, omega-3 polyunsaturated fatty acids, long-chain PUFAs.

What is it used for?

Traditional/Ethnobotanical uses

Most uses of fish oils have been based on the beneficial effects of EPA and DHA, specifically those related to the heart, inflammation, the brain, and hormones. Interest in possible health benefits followed observations that populations who ate a lot of fish, such as Eskimo and Inuit populations, had less atherosclerosis, fewer clotting disorders, and reduced inflammation. In addition, deficiencies were seen in hospitals with infants fed nonfat or low-fat diets or in patients receiving long-term (eg, 2 to 3 weeks) intravenous nutritional formulations lacking polyunsaturated fatty acids.

General uses

Evidence is strongest for lowering the risk of coronary artery disease and decreasing triglycerides in the blood. Reductions in the risk of death from any cause, cardiac death, and sudden death have been established for omega-3 fatty acid supplementation lasting at least 1 year. The US Food and Drug Administration (FDA) has approved the use of fish oil for reducing very high blood triglycerides (over 5.65 mmol/L) in adults along with eating less fatty food. Evidence favoring use of intravenous fish oil lipid emulsion is mounting from studies of severely ill and surgical patients. Evidence for a role in treating rheumatoid arthritis remains unclear but promising. No consistent relationship between fish oil consumption and reduction in the risk of stroke or maintenance in inflammatory bowel disease has been established. Other areas of interest in the use of fish oils include asthma and allergy, inadequate menstruation, mental health, and the promotion of growth and development in newborns.

What is the recommended dosage?

The American Heart Association recommends a minimum of 2 fatty fish meals per week. Clinical trials suggest fish oil supplementation of omega-3 fatty acids 1 g/day in heart disease, and when triglycerides are elevated, a minimum of omega-3 fatty acids 2 g/day up to a maximum of 4 g/day.

Contraindications have not yet been identified.

Potential for mercury ingestion. Avoid use.

None well documented.

Fish oil at dosages of EPA/DHA 2 to 5.4 g/day has been well tolerated. Mild stomach or intestinal discomfort was reported in clinical trials.

Research reveals little or no information.
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