Lipids - Essential Fatty Acids

Question 1

Essential Fatty Acids (EFAs)

Answer 1

There are two fatty acids that cannot be made in the body and so are essential in the diet. They are:
1. Linoleic acid (an omega-6 fatty acid).
2. Alpha-linolenic acid (an omega-3 fatty acid).

• Arachidonic acid was once thought to be essential in the diet, but we now know it can be made from linoleic acid.
• Humans lost the ability to introduce double bonds into fatty acids between the carbon atoms 6‒7 and 3‒4, making LA and ALA essential in the diet.
  Arachidonic = From ‘arachidic’= of the groundnut (the Greek for peanut isarachis), which has a similar fatty acid structure

Question 2

Omega 3 (ALA) and Omega 6 (LA) pathways and enzymes

Answer 2

ALA and LA have to be obtained from foods so are ‘essential’.
* From ALA (omega-3) and LA (omega-6), the next in the sequence is manufactured in the body from the preceding fatty acid in the chain, with the help of special enzymes. The most important enzyme that catalyses the chemical reaction to produce GLA and EPA is Delta-6-desaturase.

• See Diagram

Question 3

Omega 3 pathways

Answer 3

• Omega 3 –
• a-Linoleic acid (ALA) –
• Stearidonic acid –
• Eicosatetraenoic acid (EPA) –
• Docosapentaenoic acid (DPA) –
• Docosahexaenoic acid (DHA)

Question 4

Omega 6 pathways

Answer 4

• Omega 6 –
• Linoleic acid (LA) -
• Gamma Linoleic acid (GLA) -
• Di-homo-gamma linoleic acid (DGLA) –
• Arachidonic acid (AA) –
• Adrenic acid –
• Docosapentaenoic acid (DPA)

Question 5

Omega 3 pathways, foods and enzymes

Answer 5

This shows the omega-3 pathways, potential food sources of the EFAs & (enzymes).
* Omega 3 fatty acids (n=3) (flaxseed, hemp, canola, soybean, walnut)
* a-Linoleic acid (ALA)
(Delta-6 desaturase)
* Stearidonic acid –
(Elongase)
* Eicosatetraenoic acid (EPA) (fish-oils)
(Delta-5 desaturase)
* Docosapentaenoic acid (DPA) (fish-oils)
(Elongase)
* Docosahexaenoic acid (DHA) (fish oils / marine algae)
(Delta-4 desaturase)

Question 6

Omega 6 pathways, foods and enzymes

Answer 6

This shows the omega-6 pathways, potential food sources of the EFAs & (enzymes).
* Omega 6 fatty acids (n=6) (canola, corn, soybean, safflower, sunflower oil)
* Cis- linoleic acid (LA) –
(Delta-6 desaturase)
* Gamma Linoleic acid (GLA) (Blackcurrant seed oil, borage oil, evening primose oil)
(Elongase)
* Di-homo-gamma linoleic acid (DGLA) (Mothers breast milk)
(Delta-5 desaturase)
* Arachidonic acid (AA) (Animal fat)
(Elongase)
* Adrenic acid
(Delta-4 desaturase)

Question 7

Omega-6:Omega-3 ratio

Answer 7

A typical western diet is abundant in omega-6 fatty acids (plant oils, grain-fed meat and dairy), and low in omega-3 fatty acids from ALA sources (flaxseeds, pumpkin seeds) and EPA / DHA sources (oily fish).
* Human beings evolved on a diet with an omega-6:omega-3 of 1.
* In Western diets the ratio is generally around 16:1.

Question 8

EPA / DHA as Conditionally Essential Nutrients
(due to conversion from ALA)

Answer 8

• The relatively low rate of conversion of ALA to EPA / DHA suggests that EPA and DHA are conditionally essential nutrients.
• To achieve the EFSA recommended intake of 250 mg EPA / DHA, consume 2–3 portions of oily fish per week or from an algal source.
  EFSA=European Food Safety Authority

Question 9

Functions of EFAs:

Answer 9

EFAs are vital components of all cell membranes and help to maintain membrane fluidity. The fluidity of the membrane must be maintained within a certain range for the cell to function properly.
* They act with cell membrane proteins thereby affecting the transport of substances into and out of the cell.
* EFAs are key components of organelle membranes such as those of the mitochondria.
* EFAs are necessary for cell-to-cell communication.
* They are essential for foetal and child brain development.
* EFAs are precursors of eicosanoids, which are ‘local’ hormones.