Fish oil supplements are extracted from oily fish that are rich in omega-3 fatty acids, such as sardines and anchovies. Antioxidants are naturally present in their flesh which protect the fatty acids for as long as the fish is alive. However, when the fish dies the fatty acids quickly go rancid and the fish then smells rotten. Fish caught in the oceans may also contain environmental pollution. It is therefore important that a fish oil supplement is both stable and free from pollution.

Quality and Pollution

When producing a fish oil supplement it is important to add antioxidants to protect the oil from oxidation, thus making the fish oil stable. Another important quality factor is the environmental pollution in the fish used for supplement manufacturing. Small fish that are low on the food chain are less polluted than bigger and more long-lived fish. The Antarctica has one of the cleanest waters on earth, making that fish ideal for manufacturing omega-3 supplements.

Removing impurities, such as PCB and mercury, from the fish oil is a complicated process called molecular destillation, where the fish oil is separated from these substances. A high quality fish oil should undergo this process to ensure the highest possible purity.

A high quality supplement should furthermore have a bright color and neutral taste. A capsule with a brighter color is probably of higher quality. Avoid fish oil that has a strong odor or taste, which are signs of rancidity and poor quality. Fish oil and flaxseed oil should be stored in a cool and dark place, such as the refrigerator, to avoid oxidation.

Which Brand to Choose?

The quality of fish oil supplements can vary greatly between brands. Chosing the brand that best suits your needs can be difficult, because there are lots of different brands on the market. Fish oil experts recommend different brands and sometimes their brand; some recommend highly concentrated fish oils and others recommend natural fish oil with 35% omega-3 concentration. One way to find a high quality fish oil is to look for independent tests or ask a health care professional.

The Swedish laboratory AnalyCen has tested ten fish oils that was purchased in Sweden. The lab measured the peroxide value which indicates the level of oxidation. A low peroxide value means little oxidation which is good. The middle column (in the table below) shows the peroxide value that was measure instantly after purchase. The column to the right shows the peroxide value after storing the fish oil in an open container for one month, and thereby exposing it to oxygen which causes oxidation.

Product PV mekv/kg PV mekv/kg (1 month, pure oil, dark, room temp.)
Anjo Omega-3 3.2 250
Biomega 3 0.63 23
Eskimo-3 1.2 6.7
Eskimo kids 3.6 5.4
Eye q 2.9 160
Friggs Omega-3 2.4 150
Lipolar balans 2.6 96
Marlic 1.6 210
Omega-max 1000 2.2 26
Triomega Woman 0.18 36
Source: Cardinova

Dr. Andrew Stoll who is a researcher and expert on omega-3 recommends ProOmega and OmegaBrite, and a few other supplements in the book ”The Omega-3 Connection”. OmegaBrite was created by Stoll’s wife Carol A. Locke M.D. and it is a highly concentrated omega-3 supplement. It is manufactured under nitrogen to preserve potency.

Professor Tom Saldeen has concluded from his own research that natural fish oils are often more stable and potent than the supplements with higher omega-3 concentration. A natural fish oil contains approx. 35% omega-3 fatty acids, compared to the chemically modified ones that may have more than 90% omega-3 content. Professor Saldeen has created the fish oil Eskimo-3. His research have been summarized in the publication ”Fish Oil and Health with Focus on Natural Stable Fish Oil”. Garry Gordon is an M.D. and the author of the book ”The Omega-3 Miracle” where he recommends the manufacturers Iceland Health and Verified Quality.

It is important that the fish oil is stable and does not go rancid. Otherwise it may lose its health benefits and could instead have negative health effects. The oil may go rancid both inside and outside the body if it is of poor quality. Another type of omega-3 supplement is fish liver oil. Some experts say that oil made from fish liver should be avoided since it may contain too much vitamin A, which is toxic in higher doses.


Fish oil could interact with other types of medication, such as blood-thinners. If you are taking medication that could interact with omega-3 you should talk to a health care professional before using omega-3 supplements. Read more about this at