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Oily fish (oil-rich fish, pelagic fish) are those fish which have oils throughout the fillet and in the belly cavity around the gut, rather than only in the liver like white fish. Oily fish fillets may contain up to 30 percent oil, although this figure varies both within and between species. Oily fish generally swim in mid-waters or near the surface (the pelagic zone).

Oily fish are a good source of Vitamins A and D as well as being rich in Omega 3 fatty acids. For this reason the consumption of oily fish has been identified as more beneficial to humans than white fish. Amongst other benefits, studies suggest that the Omega 3 fatty acids in oily fish may help sufferers of depression, reduce the likelihood of heart disease and improve inflammatory conditions such as arthritis.

Research

French research published in 2002 in the British Medical Journal studied the relationship of the consumption of oily fish by 2,000 elderly people to their risk of getting dementia. The conclusion was that people who ate fish at least once a week had a far lower risk of being diagnosed with dementia over a seven-year period. This may be for two reasons. Firstly, the polyunsaturated fatty acids (PUFAs) in oily fish may protect brain cells against damage. Secondly, they may help keep the heart and blood vessels in good condition and thus reduce the risk of vascular dementia. Fish oils can lower levels of other fats in the blood, reducing problems caused by high blood fat levels, e.g. furring or hardening of the arteries, and high blood pressure. All these problems can lead to a higher risk of dementia.

In May 2003 experts in Circulation (Journal of the American Heart Association) wrote that eating oily fish at least twice a week may help prevent sudden death from a heart attack, as fatty acids in the fish block dangerous irregular heart rhythms. Studies of individual heart cells showed that the fatty acids blocked excessive sodium and calcium currents in the heart, which could otherwise cause dangerous, unpredictable changes in its rhythm.

In March 2005, researchers at Harvard Medical School and Brigham and Women's Hospital in the USA found that a diet rich in oily fish raised the body's production of an anti-inflammatory fat, thus possibly reducing the effects of arthritis. According to their study published in the Journal of Experimental Medicine, this diet worked best when combined with low aspirin doses.

Two months later, in May, another study, this time carried out by Edinburgh and Stirling universities in connection with Edinburgh Royal Hospital for Sick Children, suggested that oily fish could help deal with the effects of childhood autism.

Recommended consumption

In 1994, the UK Committee on Medical Aspects of Food and Nutrition Policy (COMA) recommended that people should eat at least two portions of fish per week, one of which should be oily fish.

In 2004 the Food Standards Agency published advice on the recommended minimum and maximum quantities of oily fish to be eaten per week, to balance the beneficial qualities of the Omega 3 fatty acids against the potential dangers of ingesting dioxins.

The recommendations on maximum consumption of oily fish were up to four portions (1 portion = 140g) a week for men, boys, and women past childbearing age, and up to two portions a week for women of childbearing age, including pregnant and breastfeeding women, and girls. There is no recommended limit on the consumption of white fish.

Oils from fish or plants as a source of Omega-3 fatty acids

Concerns about the dangers of overfishing, as well as the wish to find an alternative for vegetarians, means that some people have considered plants such as flax seed oil as a source of Omega-3 fatty acids. Another reason is the fact that as many types of oily fish are predators, they are higher up the food chain and thus more likely to contain toxic substances. Swordfish, bluefish and king mackerel have high levels of mercury or methylmercury and should not be eaten regularly: pregnant women should avoid eating them at all.

However, some studies suggest that these plant sources may be less effective than oily fish. The most effective component of Omega-3 fatty acids is docosahexaenoic acid (DHA) and to a lesser extent eicosapentaenoic acid (EPA). The fatty acids in flax seed oil and other plants oils contain only the precursor to DHA and EPA, alpha-linolenic acid (ALA), but they do not contain DHA and EPA themselves, so the body must convert the ALA into DHA and EPA. A healthy person's body converts only 20% of the ALA, and this figure falls when a person is elderly, unfit or ill. As plant sources already contain smaller quantities of fatty acids than oily fish, this means that a high consumption of plant sources will have less effect than a lower consumption of oily fish.

A study in the American Journal of Clinical Nutrition in 2003 examined lactating women who received supplements of 15g of flax seed oil per day. It showed an increase in EPA in their blood and milk, but no increase in DHA. DHA is required for the structure of cell membranes, in particular in the brain and the retina of the eye.

Recently Omega-3 has been extracted from algae which is claimed by those who extract it to contain both EPA and DHA .

Some oily fish

References

External links

Edible fish

Ölhaltige Fische

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Oily fish".

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