Omega-6 fatty acid

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Types of fats in food
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File:LAnumbering.png
The chemical structure of linoleic acid, a common n−6 fatty acid found in many vegetable oils.

n−6 fatty acids (popularly referred to as ω−6 fatty acids or omega-6 fatty acids) are a family of unsaturated fatty acids that have in common a final carbon–carbon double bond in the n−6 position, that is, the sixth bond, counting from the end opposite the carboxyl group[citation needed].

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 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 prostaglandins and other physiologically active molecules.

Negative health effects

Some medical research suggests that excessive levels of n−6 fatty acids, relative to n−3 (Omega-3) fatty acids, may increase the probability of a number of diseases and depression.[1][2][3]

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.[4][5]

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.[6]

Chronic excessive production of n−6 eicosanoids is associated with heart attacks, thrombotic stroke, arrhythmia, arthritis, osteoporosis, inflammation, mood disorders, obesity, and cancer.[7] Many of the medications used to treat and manage these conditions work by blocking the effects of the potent n−6 fat, arachidonic acid.[8] 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.[9] 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.[10] (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.[11][12] Many of the anti-mania medications used to treat bipolar disorder work by targeting the arachidonic acid cascade in the brain.[13]

A high consumption of omega-6 polyunsaturated fatty acids (PUFAs), which are found in most types of vegetable oil, may increase the likelihood that postmenopausal women will develop breast cancer[14]. Similar effect was observed on prostate cancer[15]. Other "analysis suggested an inverse association between total polyunsaturated fatty acids and breast cancer risk, but individual polyunsaturated fatty acids behaved differently [from each other]. [...] a 20:2 derivative of linoleic acid [...] was inversely associated with the risk of breast cancer"[16].

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.[17] 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

File:Oenothera biennis 20050825 962.jpg
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.[18]

Dietary sources of n−6 fatty acids include:[19][dead link][clarification needed]

List of n−6 fatty acids

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
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

Notes & references

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Additional sources

External links

ca:Àcid gras omega 6

da:Omega-6-fedtsyre de:Omega-n-Fettsäuren#Omega-6-Fettsäuren es:Ácidos grasos omega 6 fr:Oméga-6 hi:ओमेगा-६ वसीय अम्ल it:Omega 6 nl:Omega-6-vetzuren ja:Ω-6脂肪酸 pl:Kwasy tłuszczowe omega-6 pt:Ômega 6 sv:Omega 6-fettsyra ta:ஒமேகா-6 கொழுப்பு அமிலம் tr:Omega-6 yağ asitleri

zh:Ω-6脂肪酸
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  7. Calder, Philip C. (June 1, 2006). "n−3 polyunsaturated fatty acids, inflammation, and inflammatory diseases". American Journal of Clinical Nutrition. American Society for Nutrition. 83 (6, supplement): 1505S–1519S. PMID 16841861. 
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  14. Emily Sonestedt, Ulrika Ericson, Bo Gullberg, Kerstin Skog, Håkan Olsson, Elisabet Wirfält (2008). "Do both heterocyclic amines and omega-6 polyunsaturated fatty acids contribute to the incidence of breast cancer in postmenopausal women of the Malmö diet and cancer cohort?". The International Journal of Cancer. UICC International Union Against Cancer. 123 (7): 1637–1643. doi:10.1002/ijc.23394. PMID 10970215. Retrieved 2008-11-30. 
  15. Yong Q. Chen, at al (2007). "Modulation of prostate cancer genetic risk by omega-3 and omega-6 fatty acids". The Journal of Clinical Investigation. 117 (7): 1866–1875. doi:10.1172/JCI31494. PMC 1890998Freely accessible. PMID 17607361. Retrieved 2008-11-30. 
  16. Valeria Pala, Vittorio Krogh, Paola Muti, Véronique Chajès, Elio Riboli, Andrea Micheli, Mitra Saadatian, Sabina Sieri, Franco Berrino (July 18, 2001). "Erythrocyte Membrane Fatty Acids and Subsequent Breast Cancer: a Prospective Italian Study". JNCL. 93 (14): 1088. doi:10.1093/jnci/93.14.1088. PMID 11459870. Retrieved 2008-11-30. 
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  18. Gunstone, Frank (December 2007) "Oilseed markets: Market update: Palm oil". INFORM (AOCS) 18(12): 835-836.
  19. "Omega-6 fatty acids". WholeHealthMD. Retrieved 2008-03-23.