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The term essential implies that a nutrient is required for the body to work properly and that the consequences of deficiency are serious. Examples are the 13 essential vitamins and the essential amino acids. What evidence shows that "essential fatty acids" (EFAs) are just as essential? What defines a "deficiency"?

Please emphasize evidence for ALA (n-3 linolenic acid).

2004 PubMed article claims,

First it was shown that the differentiation and functioning of cultured brain cells requires omega-3 fatty acids. It was then demonstrated that alpha-linolenic acid (ALA) deficiency alters the course of brain development,

It unfortunately it does not give us numbers for how much ALA is required or what exactly constitutes a deficiency. Can anyone find these?

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  • I am not quite convinced anyone is saying that they are necessary to sustain life: the link you provide only claims that "the body requires them for good health". I've edited your question accordingly.
    – Sklivvz
    Jan 9, 2015 at 8:56
  • @Sklivvz, yes apparently no one is arguing that essential fatty acids are necessary to sustain life! This has answered my original question.
    – don't have to believe truth
    Jan 10, 2015 at 7:13
  • Sarcasm on the side, I've simply quoted your source.
    – Sklivvz
    Jan 10, 2015 at 10:30
  • The question for which scepticism applied to, has been answered reasonably well. If you have follow-up questions (especially those which are not about notable claims subject to scepticism) they should be asked separately on an appropriate Stack Exchange, if one exists.
    – Nij
    Oct 10, 2016 at 7:49

2 Answers 2

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According to Metabolism of α-linolenic acid in humans Prostaglandins, Leukotrienes and Essential Fatty Acids vol. 73, pages 161–168.

α-Linolenic acid (18:3n-3) is one of the two polyunsaturated fatty acids (PUFA) which are essential in the human diet. It is difficult to ascribe specific functional effects directly to 18:3n-3 and the low concentrations of this fatty acid in most mammalian cell membranes, with the exception of skin, suggest that it is unlikely to exert direct effects on cell and tissue function [reference 1]. However, the essentiality of 18:3n-3 may lie primarily in it being a substrate for the synthesis of the long-chain, more unsaturated PUFA eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)

where reference 1 is What is the role of α-linolenic acid for mammals? Lipids, 37 (2000), pp. 1113–1123

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  • 2004 PubMed article claims, "First it was shown that the differentiation and functioning of cultured brain cells requires omega-3 fatty acids. It was then demonstrated that alpha-linolenic acid (ALA) deficiency alters the course of brain development," It unfortunately it does not give us numbers for how much is required or what constitutes a deficiency. Would you be able to find this?
    – don't have to believe truth
    Oct 10, 2016 at 6:00
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    Not from my current location, maybe tomorrow, but I think only the abstract is English, rest French. em-consulte.com/article/105033/alertePM
    – DavePhD
    Oct 10, 2016 at 16:30
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    @don'thavetobelievetruth no, I can't get the French article, but this article is discussing the same information jn.nutrition.org/content/137/4/855.full
    – DavePhD
    Oct 11, 2016 at 13:22
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Yes, the so-called "essential fatty acids" are, indeed, essential" (i.e. required, but unable to be manufactured by the human body.)

The question includes a link to the Wikipedia page for essential fatty acids which defines them (in humans) as : alpha-linolenic acid and linoleic acid.

The same page explains the history of the research into them, describing a number of experiments that identified them as essential.

In the 1950s Arild Hansen showed that infants fed skimmed milk developed essential fatty acid deficiency. It was characterized by an increased food intake, poor growth, and a scaly dermatitis, and was cured by the administration of corn oil.

Later work by Hansen randomized 426 children, mainly black, to four treatments: modified cow's milk formula, skimmed milk formula, skimmed milk formula with coconut oil, or cow's milk formula with corn oil. The infants who received the skimmed milk formula or the formula with coconut oil developed essential fatty acid deficiency signs and symptoms.

[...] patients undergoing intravenous nutrition with glucose became isolated from their fat supplies and rapidly developed biochemical signs of essential fatty acid deficiency (an increase in 20:3n-9/20:4n-6 ratio in plasma) and skin symptoms.

The Wikipedia page pretty much answers the question, but I followed up a couple of sources, so I wasn't only relying on unreliable secondary sources.

This paper described three case studies of patients malnourished by a deficiency in linoleic acid. It explained they suffered "skin lesions, characterized by dryness and scaly appearance" until they were administered with Intralipid that contains linoleic acid.

It appears that the daily requirement for linoleic acid in the adult, particularly during the period of rapid anabolism, has not been clearly established.

This analysis of recommended dietary intake from 2004 summarises some of the literature.

Prospective cohort studies examined the effect of the intake of dietary fat and ω3 PUFA from plants on coronary heart disease in humans. [...] After adjustment for non-dietary risk factors and total fat intake, intake of ALA was significantly negatively correlated with risk of myocardial infarction (relative risk 0.41 for a 1% increase in energy from ALA, P < 0.01).

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  • A fat chemist I knew was criticizing someone for claiming canola oil was a good as salmon as source of Omega-3 fatty acids. He said concerning ALA, EPA, and DHA, that although the human body can convert between them, the rate may be fairly low. So if you want DHA for nerve development, then you should better get the DHA directly, instead of relying on ALA from canola oil.
    – GEdgar
    Jan 9, 2015 at 18:48
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    None of this justifies the use of supplements, except when you are receiving nutrients parenterally (i.e. through a drip)
    – Oddthinking ♦
    Jan 10, 2015 at 6:53
  • I'm abstaining re: GEdgar's comment. It's hearsay, and about different things (e.g. EPA, DHA and nerve development) to the topic of discussion.
    – Oddthinking ♦
    Jan 10, 2015 at 14:43
  • @GEdgar It was also found that the rate of fatty acid turnover is much slower in brain than in other tissues.
    – don't have to believe truth
    Oct 10, 2016 at 6:06

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