| a-Linolenic acid |
 |
 |
| Other names |
ALA; Linolenic acid; cis, cis,cis-9,12,15-Octadecatrienoic acid; (Z,Z,Z)-9,12,15-Octadecatrienoic acid; Industrene 120 |
| Identifiers |
| CAS number |
[463-40-1] |
| Properties |
| Molecular formula |
C18H30O2 |
| Molar mass |
278.43 g//mol |
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references |
a-Linolenic acid (ALA) is an organic compound found in many common vegetable oils. Systematically, it is named all-cis-9,12,15-octadecatrienoic acid.[1] 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 ?-linolenic acid, a polyunsaturated n-6 (omega-6) fatty acid.
Dietary sources
Flax is a rich source of ALA.
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).[2] 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.[5]
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.[citation needed]
Studies have found evidence that ALA is related to a lower risk of cardiovascular disease.[6][7] 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[8] and macular degeneration,[9] 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.[10]
A large 2006 study found no association between total ALA intake and overall risk of prostate cancer.[11]
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.[12][13] 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.[14] Several consortia are bringing low-ALA soy to market. DuPont's effort involves silencing the FAD2 gene that codes for ?6-desaturase, giving a soy oil with very low levels of both ALA and LA.[15]
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."[16]
Drying oils
- See main article: drying oil
ALA is the most abundant unsaturated component of several drying oils (e.g. perilla, walnut and linseed oils.)
See also
References
- ^ a b c Beare-Rogers (2001). IUPAC Lexicon of Lipid Nutrition (pdf). Retrieved on 22 February, 2006.
- ^ Chapman, David J.; De-Felice, John and Barber, James (May 1983). "Growth Temperature Effects on Thylakoid Membrane Lipid and Protein Content of Pea Chloroplasts 1". Plant Physiol 72 (1): 225–228. PMID 16662966. Retrieved on 2007-01-15.
- ^ a b c d e f g Seed Oil Fatty Acids - SOFA Database Retrieval
- ^ Li, Thomas S. C. (1999). "Sea buckthorn: New crop opportunity". Perspectives on new crops and new uses: 335–337, Alexandria, VA: ASHS Press. Retrieved on 2006-10-28.
- ^ Shiels M. Innis (2007). "Fatty acids and early human development". Early Human Development 83: 761–766. doi:10.1016/j.earlhumdev.2007.09.004.
- ^ Penny M. Kris-Etherton, William S. Harris, [and] Lawrence J. Appel, for the Nutrition Committee (2002). "Fish Consumption, Fish Oil, Omega-3 Fatty Acids, and Cardiovascular Disease" (pdf). Circulation 106 (21): 2747–2757. doi:10.1161/01.CIR.0000038493.65177.94. PMID 12438303. Retrieved on 2006-07-25. PMID 12438303
- ^ William E. Connor (2000). "Importance of n-3 fatty acids in health and disease" (pdf). American Journal of Clinical Nutrition 71 (1 Suppl.): 171S–175S. Retrieved on 2006-07-25. PMID 10617967
- ^ Brouwer IA, Katan MB, Zock PL (2004). "Dietary a-linolenic acid is associated with reduced risk of fatal coronary heart disease, but increased prostate cancer risk: a meta-analysis.". Journal of Nutrition 134 (4): 919–922. PMID 15051847. Retrieved on 2006-11-13. PMID 15051847
- ^ Eunyoung Cho, Shirley Hung, Walter C Willett, Donna Spiegelman, Eric B Rimm, Johanna M Seddon, Graham A Colditz and Susan E Hankinson (2001). "Prospective study of dietary fat and the risk of age-related macular degeneration". American Journal of Clinical Nutrition 73 (2): 209–218. PMID 11157315. Retrieved on 2006-11-13. PMID 11157315
- ^ Inger Lauritzen, Nicolas Blondeau, Catherine Heurteaux, Catherine Widmann, Georges Romey and Michel Lazdunski (2000). "Polyunsaturated fatty acids are potent neuroprotectors". The EMBO Journal 19 (8): 1784–1793. doi:10.1093/emboj/19.8.1784. PMID 10775263. Retrieved on 2005-10-06.
- ^ Koralek DO, Peters U, Andriole G, et al (2006). "A prospective study of dietary a-linolenic acid and the risk of prostate cancer (United States)". Cancer Causes Control 17 (6): 783–791. doi:10.1007/s10552-006-0014-x. PMID 16783606. Retrieved on 2007-11-14.
- ^ Fitzgerald, Anne and Brasher, Philip. "Ban on trans fat could benefit Iowa". Truth About Trade and Technology. Retrieved on January 3, 2007.
- ^ Kinney, Tony. Metabolism in Plants to Produce Healthier Food Oils (slide #2). Retrieved on 2007-01-11.
- ^ Monsanto. ADM To Process Monsanto's VISTIVE Low Linolenic Soybeans At Indiana Facility. Retrieved on 2007-01-06.
- ^ Kinney, Tony. Metabolism in Plants to Produce Healthier Food Oils. Retrieved on 2007-01-11.
- ^ Mozaffarian D (2005). "Does a-linolenic acid intake reduce the risk of coronary heart disease? A review of the evidence". Alternative therapies in health and medicine 11 (3): 24–30; quiz 31, 79. PMID 15945135.
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