Flax is a rich source of α-linolenic acid.
Seed oils are the richest sources of α-linolenic acid, notably those of rapeseed (canola), soybeans, walnuts, flaxseed (Linseed), perilla, chia and hemp. α-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 α-linolenic acid.
Hippophae rhamnoides L.
Role in nutrition and health
α-Linolenic acid, 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 α-linolenic acid. Humans, however, can obtain α-linolenic acid 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 α-linolenic acid into EPA is limited. 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.
It is generally assumed that linoleic acid (LA; 18:2, n-6) reduces EPA synthesis because of the competition between α-linolenic acid and LA for common desaturation and elongation enzymes .Studies have found evidence that α-linolenic acid is related to a lower risk of cardiovascular disease. However, the mechanism is still unclear: The body converts α-linolenic acid into the longer chain fatty acids EPA and DHA, and it is unknown whether the protective effect against cardiac arrhythmia is exerted by α-linolenic acid itself, or by these metabolic products. Some studies have linked α-linolenic acid with rapidly progressing prostate cancer and macular degeneration, increasing the risk 70% over control subjects (over those that did not receive α-linolenic acid). Research has also suggested a major neuroprotective effect of α-linolenic acid in in-vivo models of both global ischemia and KA-induced epilepsy.
A large 2006 study found no association between total α-linolenic acid intake and overall risk of prostate cancer.
When partially hydrogenated, all 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 α-linolenic acid is one reason that soybean oil undergoes partial hydrogenation. Regulations forcing the listing or banning of trans fats have spurred the development of low-α-linolenic acid 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-α-linolenic acid 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 α-linolenic acid and LA.
Dietary α-linolenic acid 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 α-linolenic acid (2 to 3 g per day) for the primary and secondary prevention of coronary heart disease."
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