Omega-3

Omega-3 is a family of organic molecules present in many foods, technically defined as "polyunsaturated fatty acids (PUFAs) with a double bond (C=C) at the third carbon atom from the end of the carbon chain".[1] They are found in both plants and animals, with dietary sources including seeds, nuts, leafy vegetables, fish, flax-fed hen's eggs, and some meats. They are most closely associated with fish oil, to the extent that many reports about the health benefits of fish oil actually refer to omega-3 from other sources.

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A wide variety of beneficial effects are claimed for them, some well-demonstrated, but most unsubstantiated. There is evidence that eating oily fish, which is rich in some types of omega-3, can prevent heart disease and other cardiovascular problems, but despite omega-3 supplements being an industry worth $25 billion in 2011, there is no evidence of a health benefit to justify taking supplements, and nor is there strong evidence as to the benefit of plant sources.[2][3][4] Additionally, there is an environmental concern related to overfishing sources (including menhaden) used to manufacture fish oil.[5][6]

There are multiple forms of Omega-3. ALA (alpha-linolenic acid) cannot be synthesised in the human body, and is mainly found in vegetables, seeds, and nuts. EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are longer-chain molecules which can be made in the body from ALA, although the process is slow, and your best bet is to eat them as well, and they can be found in foods such as oily fish.[3]

Omega-6 fatty acids have a double bond on the 6th carbon atom from the end. They are far more prevalent in western diets than omega-3, chiefly in refined vegetable oils used for frying and other cooking, and there is some (inconclusive) evidence that some omega-6 has negative health effects, with a general belief that people should reduce omega-6 and increase omega-3.[7] (If for some reason your body is deficient in omega-6 fatty acids, it can synthesize the amount it needs from omega-3 fatty acids, in the same way it can synthesize EPA/DHA from ALA.)

Sources
ALA:
  • Vegetable oil[3]
  • Rapeseed and linseed (flaxseed)[3]; however these are hard to digest so it is recommended you crush them[8]
  • Nuts, such as walnuts, pecans and hazelnuts[3]
  • Green leafy vegetables[3] including spinach, kale, Brussels sprouts, and watercress[9]
DHA/EPA:
  • Oily fish is a good source, white fish less so. Fish high in omega-3 include mackerel, herring, sprats, pilchards (sardines), etc.; trout and salmon; swordfish (though beware of the high mercury content); and fresh crab[3]; the ratios of ALA and DHA/EPA vary considerably between fishes[8]; see below for detailed health recommendations

One study showed that ALA and DHA were present at a high level in the meat of goats fed a diet rich in oil palm frond.[10]

They can also be consumed as a supplement, for instance in fish oil capsules or vegetarian products obtained from algae, although the evidence is unclear on whether you should.[3][2] A 2018 Cochrane meta-analysis of 79 research papers, however, has pointed to virtually no benefits to reducing heart disease, stroke, and death, or at least not enough benefits as promoted.[4] Some foods, including grain products, dairy, soy milk, and fruit juice, may be enriched with omega-3, either ALA, DHA, EPA, or some combination.[8]

Health claims

Omega-3 has an anti-inflammatory effect, which may be beneficial in combatting cardiovascular disease, cancer, and disorders of the immune system. In contrast, some omega-6 fatty acids increase inflammation, and there is some evidence that together they may lessen the effects of either or both.[11]

Omega-3 and specifically types in fish oil are often promoted through their association with the Inuit (because, natural Rousseauian primitives living in harmony with nature) or with another, nearly-as-mystical group, the Icelanders.[12] While the Inuit were central to the initial promotion of fish oil in the 1970s, more recent research has shown they have a genetic adaptation which allows them to metabolise omega-3 differently to other people, suggesting that while they may benefit dwellers in the Arctic with limited diets and the relevant gene, the benefits may not extend beyond that.[13]

Heart disease

Many organisations, including the American Heart Association, recommend oily fish rich in omega-3 (specifically DHA and EPA) to prevent heart disease. They reduce inflammation, which is likely to have beneficial effects, and may slightly lower blood pressure, reduce clotting, reduce irregular heartbeats, and reduce stroke risk. There is less evidence of health benefits from plant-based sources of omega-3[14] and virtually no evidence from fish oil supplements.[4]

At one point, it was thought that omega-6 fatty acids contributed to heart disease, but this is no longer the case.[15]

Brain aging

Many people believe omega-3 is good for the brain. There are a variety of claims about how omega-3 can combat "brain shrinkage" and affect behaviour and mood.[16] A recent study, carried out in the elderly over 5 years, found no evidence that omega-3 improves the memory or cognitive function.[17][18]

Child behaviour

Some studies have purported to show behavioural benefits in children given omega-3 supplements.[19] In the UK, this became a popular idea advanced in tabloid newspapers, online parenting forums, and school-gate gossip. The Daily Mail reported confidently on the wonders of fatty acids from fish-oil (while cautioning people to avoid inferior codliver oil capsules), saying, "For any parents wondering if their children have a deficiency of fatty acids, tell-tale signs are dry and lacklustre skin and hair, dry bumpy skin at the top of the arms and weak, brittle nails."[20] Fish oil products were widely promoted in British education circles, including by the manufacturers of Eye Q fish oil capsules, whose beguiling name practically promised to make your children smarter, and which donated a million pounds worth of capsules to a study by Durham education authority in the mid 2000s.[19] The Durham study was widely attacked for its failure to use a control group or any blinding, and the failure to specify outcomes to be tested, with Ben Goldacre calling it "possibly the greatest example of scientific incompetence documented from a local authority".[21]

This reached fever pitch in 2012 when a study was widely reported in the UK claiming extraordinary benefits in behaviour and reading ability when DHA (from algae rather than fish oil) was given to children, with a control group given a placebo. However NHS Choices called advice to increase fish oil consumption "highly premature", noting that the study found no overall improvement in children's reading, although there was an improvement in a small subgroup. There was also no improvement in behaviour as rated by teachers, but a small improvement as rated by parents.[22] It is uncertain if blinding could have been broken by parents smelling or otherwise examining the capsules. Another study was criticised by Ben Goldacre as involving differences in brain imaging with kids given omega-3 compared with a control, rather than any measurable effects in health or behaviour.[23] The Royal College of Psychiatrists was critical, saying: "Behavioural problems in children are multifactorial. To rely on diet alone as a strategy for managing difficult behaviour would be a mistake. The evidence base just isn't there for fish oils. Omega-3 is not a miracle cure. There is no miracle cure."[19]

Autism
See the main article on this topic: Autism

There have been claims in tabloids and other alternative health sources that consuming omega-3 in a fish-rich diet can produce significant improvements in the health and behaviour of autistic children.[24] However, a 6-month trial in Canada found no improvement.[25]

Health recommendations

The British Dietetic Association recommends two portions of fish per week, one being oily, as fish also contains many other nutrients, although they say there's no specific dose recommendation for omega-3 and they do not recommend supplements for healthy adults or children.[3] They also warn that there are risks to pregnant women or women who may be pregnant of consuming large amounts of these fish, especially larger fish like swordfish, shark, and marlin, which may be contaminated with heavy metals or dangerous molecules such as PCBs, and recommend no more than 2 portions per week for women of childbearing age and 4 portions for other adults.[3] Some fish, such as catfish and tilapia, contains unhealthy fatty acids and aren't so good for you.[14]

Dietitians of Canada (the Canadian professional body) produces specific recommendations for omega-3 consumption in those aged 19 and over: 1.6 g/day for men; 1.4 g/day for pregnant women; 1.3 g/day for breastfeeding women; 1.1 g/day for other women.[8] Web MD claims that levels suggested by different sources range from 0.5 to 1 g per day.[9] However, all these sources recommend that omega-3 is obtained from food, rather than supplements.

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See also

References
  1. See the Wikipedia article on Omega-3 fatty acid.
  2. Omega-3 Supplements and Cardiovascular Diseases, Azin Mohebi-Nejad1 and Behnood Bikdeli, Tanaffos. 2014; 13(1): 6–14.
  3. Omega-3 Food Fact Sheet, British Dietetic Association
  4. Abdelhamid AS, Brown TJ, Brainard JS, Biswas P, Thorpe GC, Moore HJ, Deane KHO, AlAbdulghafoor FK, Summerbell CD, Worthington HV, Song F, Hooper L. Omega 3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews 2018, Issue 7. Art. No.: CD003177. DOI: 10.1002/14651858.CD003177.pub3.
  5. The Original Skeptical Raptor. (August 17, 2008). Benefits of omega 3 fish oil – something’s fishy Skeptical Raptor. Retrieved January 26, 2017.
  6. Conniff, R. (December 7, 2012). The Oiliest Catch. Conservation. Retrieved January 26, 2017.
  7. See the Wikipedia article on Omega-6 fatty acid.
  8. Food Sources of Omega-3 Fats, Dietitians of Canada
  9. Your Omega-3 Family Shopping List, WebMD
  10. Omega-3 fatty acid enriched chevon (goat meat) lowers plasma cholesterol levels and alters gene expressions in rats. Ebrahimi M, Rajion MA, Meng GY, Soleimani Farjam A. Biomed. Res. Int. 2014;2014:749341. doi: 10.1155/2014/749341. Epub 2014 Feb 25.
  11. Top 10 Foods High in Omega-3, How Stuff Works
  12. The Omega-3 Miracle: The Icelandic Longevity Secret That Offers Super Protection Against Heart Disease, Cancer, Diabetes, Arthritis, Premature Aging, and Deadly Inflammation by Garry Gordon's (2004). Freedom Publishing
  13. Inuit Study Adds Twist to Omega-3 Fatty Acids’ Health Story, Carl Zimmer, New York Times, 22 Sep 2015
  14. Omega-3, Mayo Clinic
  15. What are omega-6 fatty acids? Can eating omega-6 fatty acids cause heart disease?, Mayo Clinic
  16. Maximizing Omega-3 Health Benefits, Life Extension Magazine, 2014
  17. , Time, Aug. 25, 2015
  18. NIH study shows no benefit of omega-3 or other nutritional supplements for cognitive decline, NIH
  19. Catch of the Day, Lucy Atkins, The Guardian, 2006
  20. Fish oil helps hyperactive kids, The Daily Mail
  21. Fish oil exam results fail all the tests, Ben Goldacre, Bad Science, The Guardian, 27 Sep 2008
  22. , NHS
  23. Fish oil in the Observer: the return of a $2bn friend, Ben Goldacre, Bad Science, June 2010
  24. How a fishy diet can help autistic children, Daily Mail
  25. Autism Study Fails to Show Benefit of Omega-3 Fatty Acids, Autism Speaks, April 10, 2015
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