Omega-6 fatty acid
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2008-07-14T00:06:03Z
AThing
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/* Dietary sources */
{{Merge|fatty acid|date=December 2007}}
{{For2|an explanation of ''n'' and numerical nomenclature (such as ''n''−6 or 18:2)|[[Fatty acid#Nomenclature|Nomenclature of fatty acids]]}}
{{Fats}}
[[Image:LAnumbering.png|375px|thumb|The [[chemical structure]] of [[linoleic acid]], a common ''n''−6 fatty acid found in many [[vegetable oil]]s.]]
'''''n''−6 fatty acids''' (popularly referred to as '''ω−6 fatty acids''' or '''omega-6 fatty acids''') are a family of [[unsaturated fat|unsaturated]] [[fatty acid]]s which have in common a carbon–carbon [[double bond#Bond order|double bond]] in the [[Fatty acid#Nomenclature|''n''−6]] position; that is, the sixth bond from the end of the fatty acid.
The biological effects of the ''n''−6 fatty acids are largely mediated by their conversion to n-6 eicosanoids that bind to diverse receptors found in every tissue of the body. The conversion of tissue arachidonic acid (20:4n-6) to n-6 prostaglandin and n-6 leukotriene hormones provides many targets for pharmaceutical drug development and treatment to diminish excessive n-6 actions in atherosclerosis, asthma, arthritis, vascular disease, thrombosis, immune-inflammatory processes and tumor proliferation. Competitive interactions with the [[omega-3 fatty acid|''n''−3 fatty acids]] affect the relative storage, mobilization, conversion and action of the n-3 and n-6 eicosanoid precursors. (See [[Essential fatty acid interactions]] for more information.)
==Key ''n''−6 fatty acids==
[[Linoleic acid]] (18:2, ''n''−6), the shortest-chained ''n''−6 fatty acid, is an [[essential fatty acid]]. [[Arachidonic acid]] (20:4) is a physiologically significant ''n''−6 fatty acid and is the precursor for [[prostaglandin]]s and other physiologically active molecules.
==Negative health effects==
Some medical research suggests that excessive levels of ''n''−6 fatty acids, relative to ''n''−3 fatty acids, may increase the probability of a number of diseases and depression.<ref
name="Lands2005">{{cite journal
| last = Lands
| first = William E.M.
| title = Dietary fat and health: the evidence and the politics of prevention: careful use of dietary fats can improve life and prevent disease
| journal = [[New York Academy of Sciences|Annals of the New York Academy of Sciences]]
| publisher = [[Blackwell Publishing|Blackwell]]
| volume = 1055
| pages = 179–192
| year = 2005
| month = December
| url = http://dx.doi.org/10.1196/annals.1323.028
| pmid = 16387724
| doi = 10.1196/annals.1323.028
}}</ref><ref
name=" Hibbeln2006">{{cite journal
| last = Hibbeln
| first = Joseph R.
| coauthros = Nieminen, Levi R.G.; Blasbalg, Tanya L.; Riggs, Jessica A.; and Lands, William E.M.
| title = Healthy intakes of ''n''−3 and ''n''−6 fatty acids: estimations considering worldwide diversity
| journal = American Journal of Clinical Nutrition
| publisher = American Society for Nutrition
| volume = 83
| issue = 6, supplement
| pages = 1483S–1493S
| year = 2006
| month = June
| pmid = 16841858
| url = http://www.ajcn.org/cgi/content/full/83/6/S1483
}}</ref><ref
name="Okuyama2007">{{cite journal
| last = Okuyama
| first = Hirohmi
| coauthors = Ichikawa, Yuko; Sun, Yueji; Hamazaki, Tomohito; Lands, William E.M.
| title = ω3 fatty acids effectively prevent coronary heart disease and other late-onset diseases: the excessive linoleic acid syndrome
| journal = World Review of Nutritional Dietetics
| publisher = Karger
| volume = 96
| issue = Prevention of Coronary Heart Disease
| pages = 83–103
| year = 2007
| id = ISBN 3805581793
| url = http://dx.doi.org/10.1159/000097809
| pmid = 17167282
| doi = 10.1159/000097809
}}</ref>
Modern Western diets typically have ratios of ''n''−6 to ''n''−3 in excess of 10 to 1, some as high as 30 to 1. The optimal ratio is thought to be 4 to 1 or lower.<ref
name="daley2004">{{cite journal
| last = Daley
| first = C.A.
| coauthors = Abbott, A.; Doyle, P.; Nader, G.; and Larson, S.
| title = A literature review of the value-added nutrients found in grass-fed beef products
| publisher = [[California State University, Chico]] (College of Agriculture)
| date = 2004
| url = http://www.csuchico.edu/agr/grassfedbeef/health-benefits/index.html
| accessdate = 2008-03-23
}}</ref><ref
name="simopoulos2002">{{cite journal
| last = Simopoulos
| first = Artemis P.
| title = The importance of the ratio of omega-6/omega-3 essential fatty acids
| journal = Biomedicine & Pharmacotherapy
| volume = 56
| issue = 8
| pages = 365–379
| year = 2002
| month = October
| pmid = 12442909
}}</ref>
Excess ''n''−6 fats interfere with the health benefits of ''n''−3 fats; in part because they compete for the same rate-limiting enzymes. A high proportion of ''n''−6 to ''n''−3 fat in the diet shifts the physiological state in the tissues toward the pathogenesis of many diseases: prothrombotic, proinflammatory and proconstrictive.<ref
name="simopoulos2003">{{cite journal
| last = Simopoulos
| first = Artemis P.
| title = Importance of the ratio of omega-6/omega-3 essential fatty acids: evolutionary aspects
| journal = World Review of Nutrition and Dietetics
| volume = 92
| issue = Omega-6/Omega-3 Essential Fatty Acid Ratio: The Scientific Evidence
| pages = 1–174
| year = 2003
| month = September
| publisher = Karger
| url =
| pmid = 14579680
| id = ISBN 3805576404
| doi = 10.1159/000073788
}}</ref>
Chronic excessive production of ''n''−6 eicosanoids is associated with heart attacks, thrombotic stroke, arrhythmia, arthritis, osteoporosis, inflammation, mood disorders and cancer.<ref
name="Calder2006">{{cite journal
| last = Calder
| first = Philip C.
| title = ''n''−3 polyunsaturated fatty acids, inflammation, and inflammatory diseases
| journal = American Journal of Clinical Nutrition
| publisher = American Society for Nutrition
| volume = 83
| issue = 6, supplement
| pages = 1505S–1519S
| year = 2006
| month = June
| url = http://www.ajcn.org/cgi/content/full/83/6/S1505
| pmid = 16841861
}}</ref> Many of the medications used to treat and manage these conditions work by blocking the effects of the potent ''n''−6 fat, [[arachidonic acid]].<ref
name=" Smith2008">{{cite journal
| last = Smith
| first = William L.
| title = Nutritionally essential fatty acids and biologically indispensable cyclooxygenases
| journal = [[Trends (journals)|Trends in Biochemical Sciences]]
| publisher = [[Elsevier]]
| volume = 33
| issue = 1
| pages = 27–37
| year = 2008
| month = January
| url = http://dx.doi.org/10.1016/j.tibs.2007.09.013
| pmid = 18155912
| doi = 10.1016/j.tibs.2007.09.013
}}</ref> Many steps in formation and action of n-6 hormones from n-6 arachidonic acid proceed more vigorously than the corresponding competitive steps in formation and action of n-3 hormones from n-3 eicosapentaenoic acid. <ref name=" Wada 2007">{{cite journal
| last = Wada
| first = M.
| title = Enzymes and receptors of prostaglandin pathways with arachidonic acid-derived versus eicosapentaenoic acid-derived substrates and products. Nutritionally essential fatty acids and biologically indispensable cyclooxygenases
| journal = [[J. Biol. Chem.]]
| publisher = [[ASBMB]]
| volume = 282
| issue = 31
| pages = 22254–22266
| year = 2007
| month = August 3
}}</ref> The [[COX-1]] and [[COX-2]] inhibitor medications, used to treat inflammation and pain, work by preventing the [[COX]] enzymes from turning arachidonic acid into inflammatory compounds.<ref
name="Cleland2006">{{cite journal
| last = Cleland
| first = Leslie G.
| coauthors = James, Michael J.; Proudman, Susanna M.
| title = Fish oil: what the prescriber needs to know
| journal = Arthritis Research & Therapy
| publisher = BioMed Central
| volume = 8
| issue = 1
| pages = 202
| year = 2006
| month = January
| url = http://arthritis-research.com/content/8/1/202
| pmid = 16542466
| doi = 10.1186/ar1876
}}</ref> (See [[Cyclooxygenase]] for more information.) The LOX inhibitor medications often used to treat asthma, work by preventing the LOX enzyme from converting [[arachidonic acid]] into the leukotrienes.<ref
name="Mickleborough2005">{{cite journal
| last = Mickleborough
| first = Timothy D.
| title = Dietary omega-3 polyunsaturated fatty acid supplementation and airway hyperresponsiveness in asthma
| journal = The Journal of Asthma
| publisher = [[Informa|Informa Healthcare]]
| volume = 42
| issue = 5
| pages = 305–314
| year = 2005
| month = June
| url = http://dx.doi.org/10.1081/JAS-200062950
| pmid = 16036405
| doi = 10.1081/JAS-200062950
}}</ref><ref
name="Broughton1997">{{cite journal
| last = Broughton
| first = K. Shane
| coauthors = Johnson, Cody S.; Pace, Bobin K.; Liebman, Michael; Kleppinger, Kent M.
| title = Reduced asthma symptoms with ''n''−3 fatty acid ingestion are related to 5-series leukotriene production
| journal = American Journal of Clinical Nutrition
| publisher = American Society for Nutrition
| volume = 65
| issue = 4
| pages = 1011–1017
| year = 2005
| month = April
| url = http://www.ajcn.org/cgi/reprint/65/4/1011
| pmid = 9094887
}}</ref> Many of the anti-mania medications used to treat bipolar disorder work by targeting the [[arachidonic acid]] cascade in the brain.<ref
name="lee2007">{{cite journal
| last = Lee
| first = H.J.
| coauthors = Rao, J.S.; Rapoport, S.I.; Bazinet, R.P.
| title = Antimanic therapies target brain arachidonic acid signaling: lessons learned about the regulation of brain fatty acid metabolism
| journal = Prostaglandins, Leukotrienes and Essential Fatty Acids
| publisher = [[Elsevier]]
| volume = 77
| issue = 5
| pages = 239–246
| year = 2007
| month = November
| url = http://dx.doi.org/10.1016/j.plefa.2007.10.018
| pmid = 18042366
| doi = 10.1016/j.plefa.2007.10.018}}</ref>
==Dietary Linoleic Acid Requirement==
Adding more controversy to the ''n''−6 fat issue is that the dietary requirement for linoleic acid (the key ''n''−6 fatty acid), has been seriously questioned, because of a significant methodology error discovered by University of Toronto scientist, Stephen Cunnane.<ref
name=" Cunnane2003">{{cite journal
| last = Cunnane
| first = Stephen C.
| title = Problems with essential fatty acids: time for a new paradigm?
| journal = Progress in Lipid Research
| volume = 42
| issue = 6
| pages = 544–568
| year = 2003
| month = November
| url = http://dx.doi.org/10.1016/S0163-7827(03)00038-9
| doi = 10.1016/S0163-7827(03)00038-9
| pmid = 14559071
}}</ref> Cunnane discovered that the seminal research used to determine the dietary requirement for linoleic acid was based on feeding animals linoleic acid-deficient diets, which were simultaneously deficient in ''n''−3 fats. The ''n''−3 deficiency was not taken into account. The ''n''−6 oils added back systematically to correct the deficiency also contained trace amounts of ''n''−3 fats. Therefore the researchers were inadvertently correcting the ''n''−3 deficiency as well. Ultimately, it took more oil to correct both deficiencies. According to Cunnane, this error overestimates LA requirements by 5 to 15 times.
==Dietary sources==
[[Image:Oenothera biennis 20050825 962.jpg|thumb|200px|The evening primrose flower (''O. biennis'') produces an oil containing a high content of [[γ-linolenic acid]], a type of ''n''−6 fatty acid.]]
Four major food oils (palm, soybean, rapeseed and sunflower) provide more than 100 million metric tons annually, providing more than 32 million metric tons of n-6 linoleic acid and 4 million metric tons of n-3 alpha-linolenic acid <ref Gunstone, Frank (December 2007) “Oilseed markets: Market update: Palm oil. INFORM (AOCS) 18(12): 835-836.
Dietary sources of ''n''−6 fatty acids
include:<ref name="wholehealthmd">{{cite web
| title = Omega-6 fatty acids
| work = WholeHealthMD
| url = http://209.196.51.230/ME2/dirmod.asp?sid=17E09E7CFFF640448FFB0B4FC1B7FEF0&nm=Reference+Library&type=AWHN_Supplements&mod=Supplements&mid=&id=BD5CF1DF38044FBFB58C5BFB72B262D1&tier=2
| accessdate = 2008-03-23}}</ref>
* [[poultry]]
* [[egg (food)|egg]]s
* [[cereal]]s
* [[whole-grain]] breads
* baked goods
* [[nut (fruit)|nuts]]
* most [[vegetable oil]]s
* [[oenothera|evening primrose oil]]
* [[borage|borage oil]]
* [[blackcurrant|blackcurrant seed oil]]
* [[linseed oil|flax/linseed oil]]
* [[hemp oil]]
* [[soybean oil]]
* [[cottonseed oil]]
* [[sunflower seed oil]]
* [[corn oil]]
* [[safflower oil]]
* [[pumpkin seeds]]
* acai berry
==List of ''n''−6 fatty acids==
{| class="wikitable"
! Common name
! Lipid name
! Chemical name
|-
| [[Linoleic acid]]
| 18:2 (''n''−6)
| 9,12-octadecadienoic acid
|-
| [[Gamma-linolenic acid]]
| 18:3 (''n''−6)
| 6,9,12-octadecatrienoic acid
|-
| [[Eicosadienoic acid]]
| 20:2 (''n''−6)
| 11,14-eicosadienoic acid
|-
| [[Dihomo-gamma-linolenic acid]]
| 20:3 (''n''−6)
| 8,11,14-eicosatrienoic acid
|-
| [[Arachidonic acid]]
| 20:4 (''n''−6)
| 5,8,11,14-eicosatetraenoic acid
|-
| [[Docosadienoic acid]]
| 22:2 (''n''−6)
| 13,16-docosadienoic acid
|-
| [[Docosatetraenoic acid|Adrenic acid]]
| 22:4 (''n''−6)
| 7,10,13,16-docosatetraenoic acid
|-
| [[Docosapentaenoic acid]]
| 22:5 (''n''−6)
| 4,7,10,13,16-docosapentaenoic acid
|-
| [[Calendic acid]]
| 18:3 (''n''−6)
| 8E,10E,12Z-octadecatrienoic acid
|}
==See also==
* [[Essential fatty acid interactions]]
* [[Essential nutrients]]
* [[Omega-3 fatty acid|''n''−3 fatty acid]]
* [[Omega-9 fatty acid|''n''−9 fatty acid]]
== References ==
{{reflist|2}}
=== Additional sources ===
{{refbegin}}
* {{cite news
| first = Steve
| last = Tokar
| title = Omega-6 fatty acids cause prostate tumor cell growth in culture
| url = http://www.medicalnewstoday.com/articles/29976.php
| work = Medical News Today
| publisher = MediLexicon International
| date = [[2005-09-02]]
| accessdate = 2008-03-23}}
* {{cite news
| title = Brain fatty acid levels linked to depression
| url = http://www.news-medical.net/?id=10398
| work = News-Medical.Net
| publisher = AZoNetwork
| date = [[2005-05-25]]
| accessdate = 2008-03-23}}
* {{cite journal
| last = Tribole
| first = E.F.
| title = Excess Omega-6 Fats Thwart Health Benefits from Omega-3 Fats
| journal = [[British Medical Journal]] Rapid Responses to Hooper, ''et. al.'', 2006
| url = http://www.bmj.com/cgi/eletters/332/7544/752#130637
| date = [[2006-03-27]]
| accessdate = 2008-03-23}}
{{refend}}
{{Lipids}}
[[Category:Fatty acids|ω]]
[[Category:Essential nutrients]]
[[da:Omega-6-fedtsyre]]
[[de:Omega-6-Fettsäure]]
[[es:Ácidos grasos omega 6]]
[[fr:Oméga-6]]
[[it:Omega 6]]
[[pt:Ômega 6]]
[[sv:Omega 6-fettsyra]]