Alpha-linolenic acid

Alpha-linolenic acid (ALA) is a polyunsaturated omega-3 fatty acid. It is a component of many common vegetable oils and is important to human nutrition.

Chemistry
ALA's molecular formula is C18H30O2 and molar mass 278.43 g/mol. In physiological literature, it is given the name 18:3(n-3). Its systematic chemical name is all-cis-9,12,15-octadecatrienoic acid. Chemically, 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 omega end. It is an isomer of γ-linolenic acid, an omega-6 fatty acid. Reduction of alpha-linolenic acid gives linolenyl alcohol.



Dietary sources
Seed oils are the richest sources of alpha linolenic acid, notably those of rapeseed (canola), soybeans, walnuts, flaxseed (Linseed), perilla, chia and hemp. Alpha linolenic acid is also obtained from the thylakoid membranes of the green leaves of broadleaf plants (the membranes responsible for photosynthesis). Greens, therefore, and animals that eat greens, are often a good source of ALA.

Role in nutrition and health
Alpha-linolenic acid is a member of the group of essential fatty acids called omega-3 fatty acids, so called because they are an essential dietary requirement for all mammals. Most seeds and seed oils are much richer in the omega-6 fat linoleic acid. Linoleic acid is also an essential fat, but it, and the other omega-6 fats, compete with omega-3s for positions in cell membranes and have very different effects on human health. (See Essential fatty acid interactions.)

Studies have found evidence that ALA is related to a lower risk of cardiovascular disease. However, the mechanism is still unclear: The body converts ALA into the longer chain fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (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 and macular degeneration, 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.

Linolenic acid and trans fats
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. 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-linolenic soybeans. These yield a more stable oil requiring hydrogenation less often, and therefore providing trans-free alternatives into many applications such as frying oil. Several consortia are bringing low-linolenic soy to market. DuPont's effort involves silencing the FAD2 gene that codes for Δ6-desaturase, giving soy oil very low levels of both α-linolenic and linoleic acids.

Other uses&mdash;drying oils


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