Omega-3 is a polyunsaturated fatty acid found in plant oils (ALA) and animal oils, predominantly oily fish and seafood (EPA and DHA). Omega-3 is claimed to have many health benefits.
Researchers noticed Eskimos had fewer heart attacks and strokes compared to other groups, this led them to study their diets and to determine Omega-3 fatty acids may have contributed.
Claimed benefits include lowering risk of illnesses associated with cardiovascular disease, as well as reducing the risk of other diseases from prostrate cancer, dementia to age related vision problems.
Many of the benefits have not been proven, with many studies producing inconclusive results. In some studies, some benefits shown in one group have not shown similar benefits in other groups.
Omega-3 is purported to have anti-inflammatory properties and may help with inflammation associated diseases such as rheumatoid arthritis.
Alpha linolenic acid (ALA) fatty acids are found in plants, nuts and oils. Flaxseeds, linseeds, edamame (soya beans), dark green leafy vegetables (spinach/kale), rapeseed oil, walnuts and to a lesser degree peanuts, pecans and almonds provide sources of ALA.
Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) fatty acids are found in oily fish and seafood. When Omega-3 oils are eaten, the body breaks the Omega-3 fatty acids down into DHA and EPA fatty acids. The DHA and EPA are absorbed and used by the body.
Oily fish provides a good source of Omega-3 fatty acids, especially DHA and EPA. Mackerel, herrings, sardines, salmon and tuna are all good sources of omega-3 fatty acids.
A healthy diet should include at least two portions of fish a week, including one of oily fish (such as mackerel). This may vary on a region by region basis. Certain groups such as babies, children and woman who are pregnant or breastfeeding must be careful on their oily fish intake and in such instances expert advice must be sought from a health professional for these groups.
It's important to understand the toxicity levels in fish oils, as there are many pollutants and chemicals which can build up in fish, more so the higher the fish is up the food chain. The UK Scientific Advisory Committee on Nutrition and Committee have published a detailed report on Toxicity advice on benefits and risks related to fish consumption (available here).
Alternatives to oily fish for Omega-3 fatty acids include flaxseeds, linseeds, edamame (soya beans), dark green leafy vegetables (spinach/kale), rapeseed oil, walnuts and to a lesser degree peanuts, pecans and almonds. However these generally provide sources of ALA and not DHA and EPA.
Supplements contain fish oils can provide Omega-3 fatty acids without having to eat fish. It's important to note these oils in the supplements are still processed and may not be suitable for everyone.
High dose supplements of oily fish may be dangerous as they may weaken the immune system, may contain pollutants and chemicals and also include Vitamin A, which at high does can be dangerous.
Pollutants in oily fish may be dangerous when larger amounts of fish are consumed. Dioxins and dioxin-like polychlorinated biphenyls (PCBs), methylmercury and other persistent organic pollutants such as the brominated flame retardants (BFRs), may prove detrimental to health.
Some of these pollutants may remain in the body and levels slowly build up over a number of years, this can be particularly risky to woman undergoing pregnancy. It is highly advisory to ensure only the recommended amounts of oily fish are eaten and not to consume more than these.
Some supplements provide low grade quality of fish oils which may not have adequate levels of DHA and EPA, or may contain pollutants as the oils are not from controlled sources.
Omega-3 fatty acids could also weaken the immune system, thereby making it difficult to fight infections and could contribute to thinning the blood.