Alpha-linolenic acid


Alpha-linolenic acid

Chembox new
Name = α-Linolenic acid
ImageFile = Linolenic-acid-3D-vdW.png ImageFile1 = ALAnumbering.png ImageSize1 = 350px
OtherNames = ALA; Linolenic acid; cis, cis,cis-9,12,15-Octadecatrienoic acid; (Z,Z,Z)-9,12,15-Octadecatrienoic acid; Industrene 120
Section1 = Chembox Identifiers
CASNo = 463-40-1

Section2 = Chembox Properties
Formula = C18H30O2
MolarMass = 278.43 g//mol
Density =
MeltingPt =
BoilingPt =

α-Linolenic acid (ALA) is an organic compound found in many common vegetable oils. Systematically, it is named "all"-"cis"-9,12,15-octadecatrienoic acid.cite web
author=Beare-Rogers
title=IUPAC Lexicon of Lipid Nutrition
year=2001
url=http://www.iupac.org/publications/pac/2001/pdf/7304x0685.pdf
accessmonthday=22 February | accessyear=2006
format=pdf
] In physiological literature, it is given the name 18:3 ("n"−3).

ALA is a carboxylic acid with an 18-carbon chain and three "cis" double bonds. The first double bond is located at the third carbon from the "n" end. Thus, ALA is a polyunsaturated "n"−3 (omega-3) fatty acid. It is an isomer of γ-linolenic acid, a polyunsaturated "n"−6 (omega-6) fatty acid.

Dietary sources

Seed oils are the richest sources of ALA, notably those of rapeseed (canola), soybeans, walnuts, flaxseed (Linseed), perilla, chia and hemp. ALA is also obtained from the thylakoid membranes of the green leaves of broadleaf plants (the membranes responsible for photosynthesis). [cite journal
author= Chapman, David J.; De-Felice, John and Barber, James
journal=Plant Physiol |year=1983 |month=May|volume=72 | issue=1|pages=225–228
title=Growth Temperature Effects on Thylakoid Membrane Lipid and Protein Content of Pea Chloroplasts 1
url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1066200
accessdate=2007-01-15
pmid=16662966
] Greens, therefore, and animals that eat greens, are often a good source of ALA.

Role in nutrition and health

ALA, an "n"−3 fatty acid, is a member of the group of essential fatty acids, so called because they cannot be produced within the body and must be acquired through diet. Most seeds and seed oils are much richer in an "n"−6 fatty acid, linoleic acid. Linoleic acid is also an essential fat, but it, and the other "n"−6 fats, compete with "n"−3s for positions in cell membranes and have very different effects on human health. "(See Essential fatty acid interactions.")

Eicosapentaenoic acid (EPA; 20:5, "n"−3) and docosahexaenoic acid (DHA; 22:6, "n"−3) play a vital role in many metabolic processes. Although these two fatty acids are readily available from fish, these marine-derived fatty acids can also be synthesized by humans from ALA. Humans, however, can obtain ALA only through their diets, because the absence of the required 12- and 15-desaturase enzymes makes de novo synthesis from stearic acid impossible. Furthermore, conversion of dietary ALA into EPA is limited. Because the efficacy of "n"−3 long-chain polyunsaturated fatty acid (LC-PUFA) synthesis decreases down the cascade of ALA conversion, DHA synthesis from ALA is even more restricted than that of EPA. [cite journal
author=Shiels M. Innis
year = 2007
title = Fatty acids and early human development
journal = Early Human Development
volume = 83
pages = 761–766
doi = 10.1016/j.earlhumdev.2007.09.004
]

It is generally assumed that linoleic acid (LA; 18:2, "n"−6) reduces EPA synthesis because of the competition between ALA and LA for common desaturation and elongation enzymes.Fact|date=March 2008

Studies have found evidence that ALA is related to a lower risk of cardiovascular disease. [cite journal
author = Penny M. Kris-Etherton, William S. Harris, [and] Lawrence J. Appel, for the Nutrition Committee
year = 2002
title = Fish Consumption, Fish Oil, Omega-3 Fatty Acids, and Cardiovascular Disease
journal = Circulation
volume = 106
issue = 21
pages = 2747–2757
url = http://circ.ahajournals.org/cgi/content/full/106/21/2747
format=pdf
accessdate = 2006-07-25
doi = 10.1161/01.CIR.0000038493.65177.94
pmid = 12438303
PMID 12438303
] [cite journal
author = William E. Connor
year = 2000
title = Importance of "n"−3 fatty acids in health and disease
journal = American Journal of Clinical Nutrition
volume = 71
issue = 1 Suppl.
pages = 171S–175S
url = http://www.ajcn.org/cgi/reprint/71/1/171S
format=pdf
accessdate = 2006-07-25
PMID 10617967
] However, the mechanism is still unclear: The body converts ALA into the longer chain fatty acids EPA and DHA, and it is unknown whether the protective effect against cardiac arrhythmia is exerted by ALA itself, or by these metabolic products. Some studies have linked ALA with rapidly progressing prostate cancer [cite journal
author = Brouwer IA, Katan MB, Zock PL
year = 2004
title = Dietary α-linolenic acid is associated with reduced risk of fatal coronary heart disease, but increased prostate cancer risk: a meta-analysis.
journal = Journal of Nutrition
volume = 134
issue = 4
pages = 919–922
url = http://jn.nutrition.org/cgi/content/full/134/4/919
accessdate = 2006-11-13
pmid = 15051847
PMID 15051847
] and macular degeneration, [cite journal
author = Eunyoung Cho, Shirley Hung, Walter C Willett, Donna Spiegelman, Eric B Rimm, Johanna M Seddon, Graham A Colditz and Susan E Hankinson
year = 2001
title = Prospective study of dietary fat and the risk of age-related macular degeneration
journal = American Journal of Clinical Nutrition
volume = 73
issue = 2
pages = 209–218
url = http://www.ajcn.org/cgi/content/full/73/2/209
accessdate = 2006-11-13
pmid = 11157315
PMID 11157315
] increasing the risk 70% over control subjects (over those that did not receive ALA). Research has also suggested a major neuroprotective effect of ALA in in-vivo models of both global ischemia and KA-induced epilepsy. [cite journal
author = Inger Lauritzen, Nicolas Blondeau, Catherine Heurteaux, Catherine Widmann, Georges Romey and Michel Lazdunski
year = 2000
title = Polyunsaturated fatty acids are potent neuroprotectors
journal = The EMBO Journal
volume = 19
issue = 8
pages = 1784–1793
url = http://embojournal.npgjournals.com/cgi/content/full/19/8/1784
accessdate = 2005-10-06
pmid = 10775263
doi = 10.1093/emboj/19.8.1784
]

A large 2006 study found no association between total ALA intake and overall risk of prostate cancer.cite journal |author=Koralek DO, Peters U, Andriole G, "et al" |title=A prospective study of dietary α-linolenic acid and the risk of prostate cancer (United States) |journal=Cancer Causes Control |volume=17 |issue=6 |pages=783–791 |year=2006 |pmid=16783606 |doi=10.1007/s10552-006-0014-x |accessdate=2007-11-14]

ALA

When partially hydrogenated, all unsaturated fatty acids form trans fats. Soybeans are the largest source of edible oils in the U.S., and 40% of soy oil production is partially hydrogenated. [cite journal
url = http://www.truthabouttrade.org/article.asp?id=6669
title = Ban on trans fat could benefit Iowa
journal = Truth About Trade and Technology
accessdate = January 3
author = Fitzgerald, Anne and Brasher, Philip
accessyear = 2007
] [cite web
author = Kinney, Tony
title= Metabolism in Plants to Produce Healthier Food Oils (slide #2)
url= http://www.metabolicengineering.gov/me2005/Kinney.pdf
accessdate= 2007-01-11
] The low oxidative stability of ALA is one reason that soybean oil undergoes partial hydrogenation. Regulations forcing the listing or banning of trans fats have spurred the development of low-ALA soybeans. These yield a more stable oil requiring hydrogenation less often, and therefore providing trans-free alternatives into many applications such as frying oil. [cite web
url =http://www.monsanto.com/monsanto/layout/media/06/01-12-06.asp
author = Monsanto
title = ADM To Process Monsanto's VISTIVE Low Linolenic Soybeans At Indiana Facility
accessdate = 2007-01-06
] Several consortia are bringing low-ALA soy to market. DuPont's effort involves silencing the FAD2 gene that codes for Δ6-desaturase, giving a soy oil with very low levels of both ALA and LA. [cite web
author = Kinney, Tony
title= Metabolism in Plants to Produce Healthier Food Oils
url= http://www.metabolicengineering.gov/me2005/Kinney.pdf
accessdate= 2007-01-11
]

Cardiovascular

Dietary ALA has been assessed for its role in cardiovascular health. Clinical benefits have been seen in some but not all studies. Still, a review in 2005 concluded "The weight of the evidence favors recommendations for modest dietary consumption of ALA (2 to 3 g per day) for the primary and secondary prevention of CHD."cite journal |author=Mozaffarian D |title=Does α-linolenic acid intake reduce the risk of coronary heart disease? A review of the evidence |journal=Alternative therapies in health and medicine |volume=11 |issue=3 |pages=24–30; quiz 31, 79 |year=2005 |pmid=15945135 |doi=]

Drying oils

ALA is the most abundant unsaturated component of several drying oils (e.g. perilla, walnut and linseed oils.)

ee also

*Essential fatty acid
*List of "n"−3 fatty acids
*Essential nutrient

References


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