The Nature Of Omega 3 Fatty Acids

What does the term "Omega 3 EFA" mean?

We define the term "Omega 3 EFA" to mean the 3 fatty acids ALA, EPA and DHA, all of which are important components of the human diet.

We require two fatty acids that cannot be made by the body. They must therefore be obtained from food and are known as Essential Fatty Acids (EFAs). They are a subset of the Polyunsaturated Fatty Acid (PUFA) family.

Strictly speaking there is only one omega 3 (n-3) EFA. That is Alpha-Linolenic Acid (ALA). Likewise, Linoleic Acid (LA) is the only omega 6 (n-6) EFA.

However, we include the "non-essential" PUFAs Eicosapentaenoic Acid (EPA) and Docosahexaenoic Acid (DHA) within the scope of the omega 3 theme because we strongly believe they should be included in our diets.

Out of respect for the official convention, and to avoid confusion, we will use the term "PUFA" rather than "EFA" when we talk about n-3 and n-6 fatty acids. Here is a summary of the main n-3 and n-6 PUFAs:

Omega 3 (n-3)

IUPAC Abbreviation Trivial Name (Common Abbreviation) Parent or Derivative
18:3n-3 Alpha-Linolenic Acid (ALA) Parent
18:4n-3 Stearidonic Acid (SA) Derivative
20:5n-3 Eicosapentaenoic Acid (EPA) Derivative
22:6n-3 Docosahexaenoic Acid (DHA) Derivative

Omega 6 (n-6)

IUPAC Abbreviation Trivial Name (Common Abbreviation) Parent or Derivative
18:2n-6 Linoleic Acid (LA) Parent
18:3n-6 Gamma-Linolenic Acid (GLA) Derivative
20:3n-6 Dihomo-Gamma-Linolenic Acid (DGLA) Derivative
20:4n-6 Arachidonic Acid (AA) Derivative

The derivative members of both groups can be made by the body from the parent members of those groups via their metabolic pathways. Note the potentially confusing use of "Linolenic" in the names of GLA and DGLA where you might have expected to see "Linoleic" instead (as in the n-6 parent). GLA is actually an isomer of ALA.

Find out about metabolic pathways

Shorthand naming convention (IUPAC abbreviation)

The NN:N part means Number of carbon atoms:Number of double bonds. The n-N part (where n stands for "omega") refers to the position of the first double bond in the fatty acid molecule, counting the number of carbon atoms from the methyl group (CH3) or Omega end of the molecule. This convention was suggested by Holman in 1964.

Why is n-6 PUFA consumption relevant to n-3 PUFAs?

The ratio of n-6 to n-3 fatty acids consumed in our diet is widely considered to be an important health factor because:

What about the non-essential n-3 PUFAs?

We should consider EPA and DHA essential too: It makes sense to regard the two ALA derivatives EPA and DHA as essential to our diet because they perform unique physiological functions and can only be made in limited quantities from ALA. Actual conversion rates are open to conjecture.

Technically EPA and DHA are considered non-essential because the body can make them from ALA.

However their conversion rate via the n-3 metabolic pathway is often too low to provide adequate quantities due to enzyme deficiencies or other factors.

EPA and DHA perform specialized physiological functions that ALA cannot.

We shall treat EPA and DHA as being as essential to the human diet as ALA, notwithstanding their official classification as "non-essential". We therefore include them in the context of the term "Omega 3 EFA".

We shall place a smaller emphasis on SA because it is not as important for our health as ALA, EPA and DHA and is not found in many foods. SA has interesting potential because it exhibits a significantly higher rate of conversion into EPA than ALA does.

What are the main sources of n-3 PUFAs?

ALA is primarily obtained from plants (which, unlike animals, can make it) including chia seeds, sacha inchi seeds, flax seeds, walnuts and - in smaller quantities - various vegetables.

EPA and DHA are obtained from fatty fish such as salmon, tuna, mackerel and herring. They are also found in algae.

ALA, EPA and DHA are all present in meat, dairy products and eggs, although in smaller quantities than in seeds such as chia, sacha inchi and flax.

SA occurs naturally in only a few plant-based foods such as blackcurrant seed oil and echium. It may in future be introduced into other food sources, such as canola, via genetic engineering.

Get information about the important non-vegetarian dietary sources of omega 3 PUFAs
Get information about the important vegetarian dietary sources of omega 3 PUFAs