''alpha''-Linolenic acid (ALA), also known as α-Linolenic acid (from

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''alpha'' meaning "first" and ''linon'' meaning

flax Flax, also known as common flax or linseed, is a flowering plant, ''Linum usitatissimum'', in the family Linaceae. It is cultivated as a food and fiber crop in regions of the world with temperate climates. Textiles made from flax are known in ...

), is an ''n''−3, or omega-3, essential fatty acid. ALA is found in many seeds and oils, including flaxseed,

walnut A walnut is the edible seed of a drupe of any tree of the genus ''Juglans'' (family Juglandaceae), particularly the Persian or English walnut, '' Juglans regia''. Although culinarily considered a "nut" and used as such, it is not a true ...

s, chia,

hemp Hemp, or industrial hemp, is a botanical class of '' Cannabis sativa'' cultivars grown specifically for industrial or medicinal use. It can be used to make a wide range of products. Along with bamboo, hemp is among the fastest growing plants ...

, and many common

vegetable oil Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or f ...

s. In terms of its

structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such a ...

, it is named ''all''-''cis''-9,12,15-octadecatrienoic acid. In physiological literature, it is listed by its lipid number, 18:3, and (''n''−3). It is a

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxyli ...

with an 18-carbon chain and three '' cis''

double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betwee ...

s. The first double bond is located at the third carbon from the methyl end of the fatty acid chain, known as the ''n'' end. Thus, α-linolenic acid is a polyunsaturated ''n''−3 (omega-3) fatty acid. It is an

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Is ...

of gamma-linolenic acid (GLA), an 18:3 (''n''−6) fatty acid (i.e., a polyunsaturated omega-6 fatty acid with three double bonds).

Etymology

The word ''linolenic'' is an irregular derivation from ''linoleic'', which itself is derived from the

word ''linon'' (

). ''Oleic'' means "of or relating to

oleic acid Oleic acid is a fatty acid that occurs naturally in various animal and vegetable fats and oils. It is an odorless, colorless oil, although commercial samples may be yellowish. In chemical terms, oleic acid is classified as a monounsaturated o ...

" because saturating linoleic acid's omega-6 double bond produces oleic acid.

Dietary sources

Seed oils are the richest sources of α-linolenic acid, notably those of hempseed, chia, perilla, flaxseed (

linseed oil Linseed oil, also known as flaxseed oil or flax oil (in its edible form), is a colourless to yellowish oil obtained from the dried, ripened seeds of the flax plant (''Linum usitatissimum''). The oil is obtained by pressing, sometimes followed by ...

), rapeseed (

canola Close-up of canola blooms Canola flower Rapeseed oil is one of the oldest known vegetable oils. There are both edible and industrial forms produced from rapeseed, the seed of several cultivars of the plant family Brassicaceae. Historically, ...

), and

soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu ...

s. α-Linolenic acid is also obtained from the thylakoid membranes in the leaves of '' Pisum sativum'' (pea leaves). Plant

chloroplasts A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

consisting of more than 95 percent of photosynthetic thylakoid membranes are highly fluid due to the large abundance of linolenic acid, that shows up as sharp resonances in high-resolution carbon-13 NMR spectra, invariably. Some studies state that ALA remains stable during processing and cooking. However, other studies state that ALA might not be suitable for baking, as it will

polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

ize with itself, a feature exploited in

paint Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture. Paint can be made in many ...

with transition metal catalysts. Some ALA may also oxidize at baking temperatures. ALA percentages in the table below refer to the oils extracted from each item.

Potential role in nutrition and health

Although the best source of ALA is seeds, most seeds and seed oils are much richer in an ''n''−6 fatty acid,

linoleic acid Linoleic acid (LA) is an organic compound with the formula COOH(CH2)7CH=CHCH2CH=CH(CH2)4CH3. Both alkene groups are ''cis''. It is a fatty acid sometimes denoted 18:2 (n-6) or 18:2 ''cis''-9,12. A linoleate is a salt or ester of this acid. ...

. Exceptions include flaxseed (must be ground for proper nutrient absorption) and chia seeds. Linoleic acid is the other essential fatty acid, but it, and the other ''n''−6 fatty acids, compete with ''n''−3s for positions in cell membranes and have very different effects on human health. There is a complex set of

essential fatty acid interactions The two essential fatty acids are omega 3 and omega 6, which are required for a good human health. However, the effects of the ω-3 (omega-3) and ω-6 (omega-6) essential fatty acids (EFAs) are characterized by their interactions. The interac ...

. α-Linolenic acid can only be obtained by humans through their diets because the absence of the required 12- and 15-desaturase enzymes makes ''de novo'' synthesis from

stearic acid Stearic acid ( , ) is a saturated fatty acid with an 18-carbon chain. The IUPAC name is octadecanoic acid. It is a waxy solid and its chemical formula is C17H35CO2H. Its name comes from the Greek word στέαρ "''stéar''", which means ta ...

impossible. Eicosapentaenoic acid (EPA; 20:5, ''n''−3) and

docosahexaenoic acid Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is a primary structural component of the human brain, cerebral cortex, skin, and retina. In physiological literature, it is given the name 22:6(n-3). It can be synthesized from alpha-lin ...

(DHA; 22:6, ''n''−3) are readily available from fish and algae oil and play a vital role in many metabolic processes. These can also be synthesized by humans from dietary α-linolenic acid: ALA → stearidonic acid → eicosatetraeonic acid → eicosapentaenoic acid → docosapentaenoic acid → 9,12,15,18,21-tetracosapentaenoic acid → 6,9,12,15,18,21-tetracosahexaenoic acid →

, but with an efficiency of only a few percent. Because the efficacy of ''n''−3 long-chain polyunsaturated fatty acid (LC-PUFA) synthesis decreases down the cascade of α-linolenic acid conversion, DHA synthesis from α-linolenic acid is even more restricted than that of EPA. Conversion of ALA to DHA is higher in women than in men.

Stability and hydrogenation

Compared to many other oils, α-Linolenic acid is more susceptible to oxidation and will become rancid more quickly. Oxidative instability of α-linolenic acid is one reason why producers choose to partially

hydrogenate Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organ ...

oils containing α-linolenic acid, such as

soybean oil Soybean oil (British English: soyabean oil) is a vegetable oil extracted from the seeds of the soybean (''Glycine max''). It is one of the most widely consumed cooking oils and the second most consumed vegetable oil. As a drying oil, processe ...

Soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu ...

s are the largest source of edible oils in the U.S., and, as of a 2007 study, 40% of soy oil production was partially hydrogenated. However, when partially hydrogenated, part of the unsaturated fatty acids become unhealthy

trans fats Trans fat, also called trans-unsaturated fatty acids, or trans fatty acids, is a type of unsaturated fat that naturally occurs in small amounts in meat and milk fat. It became widely produced as an unintentional byproduct in the industrial pro ...

. Consumers are increasingly avoiding products that contain trans fats, and governments have begun to ban trans fats in food products. These regulations and market pressures have spurred the development of low-α-linolenic acid soybeans. These new soybean varieties yield a more stable oil that doesn't require hydrogenation for many applications, thus providing trans fat-free products, such as frying oil. Several consortia are bringing low-α-linolenic acid soy to market.

DuPont DuPont de Nemours, Inc., commonly shortened to DuPont, is an American multinational chemical company first formed in 1802 by French-American chemist and industrialist Éleuthère Irénée du Pont de Nemours. The company played a major role in ...

's effort involves

silencing Silencing is a visual illusion in which a set of objects that change iluminancehueΔ⁶-desaturase, giving a soy oil with very low levels of both α-linolenic acid and linoleic acid.

Monsanto Company The Monsanto Company () was an American agrochemical and agricultural biotechnology corporation founded in 1901 and headquartered in Creve Coeur, Missouri. Monsanto's best known product is Roundup, a glyphosate-based herbicide, developed i ...

has introduced to the market Vistive, their brand of low α-linolenic acid soybeans, which is less controversial than

GMO A genetically modified organism (GMO) is any organism whose genetic material has been altered using genetic engineering techniques. The exact definition of a genetically modified organism and what constitutes genetic engineering varies, with ...

offerings, as it was created via conventional breeding techniques.

Health

According to a 2012 review, higher ALA consumption is associated with a moderately lower risk of

cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, hea ...

, but wide variation in results across multiple studies highlights the need for additional research before drawing firm conclusions. Dietary ALA intake can improve lipid profiles by decreasing triglycerides, total cholesterol,

high-density lipoprotein High-density lipoprotein (HDL) is one of the five major groups of lipoproteins. Lipoproteins are complex particles composed of multiple proteins which transport all fat molecules (lipids) around the body within the water outside cells. They are t ...

and

low-density lipoprotein Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein that transport all fat molecules around the body in extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall densi ...

cholesterol. A 2021 review found that ALA intake is associated with a reduced risk of mortality from all causes, cardiovascular disease and coronary heart disease but a slightly higher risk of cancer mortality.

History

In 1887, linolenic acid was discovered and named by the Austrian chemist Karl Hazura of the Imperial Technical Institute at Vienna (although he didn't separate its isomers). α-Linolenic acid was first isolated in pure form in 1909 by Ernst Erdmann and F. Bedford of the University of Halle an der Saale, Germany, and by Adolf Rollett of the Universität Berlin, Germany, working independently, as cited in J. W. McCutcheon's synthesis in 1942, and referred to in Green and Hilditch's 1930s survey. It was first artificially synthesized in 1995 from C6 homologating agents. A Wittig reaction of the phosphonium salt of ''Z-Z'')-nona-3,6-dien-1-ylriphenylphosphonium bromide with methyl 9-oxononanoate, followed by saponification, completed the synthesis.

References

{{DEFAULTSORT:Linolenic acid, alpha- 5α-Reductase inhibitors Fatty acids Essential fatty acids Essential nutrients Alkenoic acids Semiochemicals Insect pheromones