Omega-6 fatty acid

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For an explanation of n and numerical nomenclature (such as n−6 or 18:2), see Nomenclature of fatty acids.
The chemical structure of linoleic acid, a common n−6 fatty acid found in many vegetable oils.
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 which have in common a carbon–carbon double bond in the 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 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.)

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[edit] 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.

[edit] 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.[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 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]

[edit] 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.[14] 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.

[edit] Dietary sources

The evening primrose flower (O. biennis) produces an oil containing a high content of γ-linolenic acid, a type of n−6 fatty acid.
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 [15]

[edit] 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

[edit] See also

[edit] References

  1. ^ Lands, William E.M. (December 2005). "Dietary fat and health: the evidence and the politics of prevention: careful use of dietary fats can improve life and prevent disease". Annals of the New York Academy of Sciences 1055: 179–192. Blackwell. doi:10.1196/annals.1323.028. PMID 16387724. 
  2. ^ Hibbeln, Joseph R. (June 2006). "Healthy intakes of n−3 and n−6 fatty acids: estimations considering worldwide diversity.". American Journal of Clinical Nutrition 83 (6, supplement): 1483S–1493S. American Society for Nutrition. PMID 16841858. 
  3. ^ Okuyama, Hirohmi; Ichikawa, Yuko; Sun, Yueji; Hamazaki, Tomohito; Lands, William E.M. (2007). "ω3 fatty acids effectively prevent coronary heart disease and other late-onset diseases: the excessive linoleic acid syndrome". World Review of Nutritional Dietetics 96 (Prevention of Coronary Heart Disease): 83–103. Karger. doi:10.1159/000097809. PMID 17167282. ISBN 3805581793. 
  4. ^ Daley, C.A.; Abbott, A.; Doyle, P.; Nader, G.; and Larson, S. (2004). "A literature review of the value-added nutrients found in grass-fed beef products". California State University, Chico (College of Agriculture). 
  5. ^ Simopoulos, Artemis P. (October 2002). "The importance of the ratio of omega-6/omega-3 essential fatty acids". Biomedicine & Pharmacotherapy 56 (8): 365–379. PMID 12442909. 
  6. ^ Simopoulos, Artemis P. (September 2003). "Importance of the ratio of omega-6/omega-3 essential fatty acids: evolutionary aspects". World Review of Nutrition and Dietetics 92 (Omega-6/Omega-3 Essential Fatty Acid Ratio: The Scientific Evidence): 1–174. Karger. doi:10.1159/000073788. PMID 14579680. ISBN 3805576404. 
  7. ^ Calder, Philip C. (June 2006). "n−3 polyunsaturated fatty acids, inflammation, and inflammatory diseases". American Journal of Clinical Nutrition 83 (6, supplement): 1505S–1519S. American Society for Nutrition. PMID 16841861. 
  8. ^ Smith, William L. (January 2008). "Nutritionally essential fatty acids and biologically indispensable cyclooxygenases". Trends in Biochemical Sciences 33 (1): 27–37. Elsevier. doi:10.1016/j.tibs.2007.09.013. PMID 18155912. 
  9. ^ Wada, M. (August 3 2007). "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". J. Biol. Chem. 282 (31): 22254–22266. ASBMB. 
  10. ^ Cleland, Leslie G.; James, Michael J.; Proudman, Susanna M. (January 2006). "Fish oil: what the prescriber needs to know". Arthritis Research & Therapy 8 (1): 202. BioMed Central. doi:10.1186/ar1876. PMID 16542466. 
  11. ^ Mickleborough, Timothy D. (June 2005). "Dietary omega-3 polyunsaturated fatty acid supplementation and airway hyperresponsiveness in asthma". The Journal of Asthma 42 (5): 305–314. Informa Healthcare. doi:10.1081/JAS-200062950. PMID 16036405. 
  12. ^ Broughton, K. Shane; Johnson, Cody S.; Pace, Bobin K.; Liebman, Michael; Kleppinger, Kent M. (April 2005). "Reduced asthma symptoms with n−3 fatty acid ingestion are related to 5-series leukotriene production". American Journal of Clinical Nutrition 65 (4): 1011–1017. American Society for Nutrition. PMID 9094887. 
  13. ^ Lee, H.J.; Rao, J.S.; Rapoport, S.I.; Bazinet, R.P. (November 2007). "Antimanic therapies target brain arachidonic acid signaling: lessons learned about the regulation of brain fatty acid metabolism". Prostaglandins, Leukotrienes and Essential Fatty Acids 77 (5): 239–246. Elsevier. doi:10.1016/j.plefa.2007.10.018. PMID 18042366. 
  14. ^ Cunnane, Stephen C. (November 2003). "Problems with essential fatty acids: time for a new paradigm?". Progress in Lipid Research 42 (6): 544–568. doi:10.1016/S0163-7827(03)00038-9. PMID 14559071. 
  15. ^ Omega-6 fatty acids. WholeHealthMD. Retrieved on 2008-03-23.

[edit] Additional sources

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