Essential fatty acids: definition, synthesis, role, and foods

Essential fatty acids or EFAs are unsaturated fatty acids that cannot be synthesized by animals, and, like other essential nutrients, must be obtained from the diet. They are linoleic acid and alpha-linolenic acid.
Animals cannot synthesize the two fatty acids due to the lack of delta-12 desaturase (E.C. and delta-15 desaturase (EC[1][9][15] These enzymes introduce cis double bonds beyond carbon 9, and are present in plants and some microorganisms such as some bacteria, fungi and molds.[10]

  • Delta-12 desaturase catalyzes the synthesis of linoleic acid from oleic acid, by introducing a double bond at delta-12 position, namely, between carbons 6 and 7 from the methyl end of the fatty acid.[15]
  • Delta-15 desaturase or omega-3 desaturase or fatty acid desaturase 3 catalyzes the synthesis of alpha-linolenic acid from linoleic acid by introducing a double bond at delta-15 position, namely, between carbons 3 and 4 from the methyl end of the fatty acid. The enzyme is only present in the plastids and in the endoplasmic reticulum of phytoplankton and vascular terrestrial plants.[1][9]
Synthesis of the essential fatty acids linoleic acid and alpha-linolenic acid
Synthesis of EFAs

Linoleic acid and alpha-linolenic acid are the precursors to omega-6 polyunsaturated fatty acids and omega-3 polyunsaturated fatty acids. In the absence of dietary EFAs, a rather rare condition, the other omega-3 and omega-6 fatty acids become essential, too. For this reason, these lipids are defined by some as conditionally essential fatty acids.[9]
It should be pointed out that all essential fatty acids are polyunsaturated fatty acids, but not all polyunsaturated fatty acids are essential, such as those belonging to the omega-7 and omega-9 families.


The discovery

The first evidence of the existence of essential fatty acids dates back to 1918, when Hans Aron suggested that dietary fat could be essential for the healthy growth of animals and that, in addition to their caloric contribution, there was a inherent nutritive value due to the presence of certain lipid molecules.[2]
In 1927, Herbert M. Evans and George Oswald Burr demonstrated that, despite the addition of vitamins A, D, and E to the diet, a deficiency of fat severely affected both growth and reproduction of experimental animals. Therefore, they suggested the presence of an essential substance in the fat that they called vitamin F.[11]
Eleven years after Aron work, in 1929, Burr and his wife Mildred Lawson hypothesized that warm-blooded animals were not able to synthesize appreciable amounts of certain fatty acids.[7] One year later, they discovered that linoleic acid was essential for animals, and it was they who coined the term essential fatty acid.[8][19] However, EFA deficiency in humans was first described by Arild Hansen only in 1958, in infants fed a milk-based formula lacking them.[14]
And in 1964, thanks to the research of Van Dorp and Bergstroem, one of their biological functions was discovered: being the precursors for the synthesis of prostaglandins.[3][21]


Essential fatty acids play important biological functions.

  • Linoleic acid and alpha-linolenic acid can be used as an energy source through beta-oxidation.[22]
  • Linoleic acid and alpha-linolenic acid are the precursors to omega-6 polyunsaturated fatty acids and omega-3 polyunsaturated fatty acids. Indeed, many animals, including humans, can synthesize, although with variable efficiency, the other omega-3 and omega-6 polyunsaturated fatty acids, for example arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid.[5][6][18]
  • Essential fatty acids are structural components of cellular membranes, modulating, for example, their fluidity.[20][22]
  • They are essential in the skin, especially linoleic acid in sphingolipids of the stratum corneum, where they contribute to the formation of the barrier against water loss.[23]
  • They have a crucial role in the prevention of many diseases, particularly coronary heart disease.[12][16]

Food sources

Linoleic acid is the most abundant polyunsaturated fatty acid in the Western diet, and accounts for 85-90 percent of dietary omega-6 polyunsaturated fatty acids.[13] The richest dietary sources are vegetable oils and seeds of many plants.[4]

Food sources Linoleic acid (mg/g)
Safflower oil ∼ 740
Sunflower oil ∼ 600
Soybean oil ∼ 530
Corn oil ∼ 500
Cottonseed oil ∼ 480
Walnuts ∼ 340
Brazil nuts ∼ 250
Peanut oil ∼ 240
Rapeseed oil ∼ 190
Peanuts ∼ 140
Flaxseed oil ∼ 135

Linoleic acid is present in fair amounts also in animal products such as chicken eggs or lard, because it is present in their feed.[9]
It should be noted that some of the major sources of linoleic acid, such as walnuts, flaxseed oil, soybean oil, and rapeseed oil are also high in alpha-linolenic acid.[17]
Some of the richest dietary sources of alpha-linolenic acid are flaxseed oil, ~ 550 mg/g, rapeseed oil, ~ 85 mg/g, and soybean oil, ~ 75 mg/g. Other foods rich in alpha-linolenic acid include nuts, ~ 70 mg/g, and soybeans, ~ 10 mg/g.[1]


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  3. ^ Bergstroem S., Danielsson H., Klenberg D., Samuelsson B. The enzymatic conversion of essential fatty acids into prostaglandins. J Biol Chem 1964;239:PC4006-8. doi:10.1016/S0021-9258(18)91234-2
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