Biochemistry of Omega 3 Fatty Acids
Fatty acid basics
Detailed explanations of the biochemistry of omega 3 fatty acids and other lipids, written by highly qualified experts, are available in numerous web sites and books.
We provide only a high-level
summary because we wish to focus on the practical aspects of obtaining omega 3 fatty acids effectively from our diets.
Fatty acid molecules
All fatty acid molecules consist of a Carboxyl or Acid (COOH) group attached to a carbon chain. A Methyl group (CH3) is usually attached to the other end of the carbon chain. Each carbon atom is connected to two hydrogen atoms except where one or more double bonds occur (see following section).
The difference between saturated and unsaturated fatty acids
When a saturated fatty acid has one or more double bonds inserted into its carbon chain (as occurs in plant biochemistry) it becomes an unsaturated fatty acid.
The double bonds make unsaturated fatty acid molecules chemically active, allowing them to perform important physiological tasks. These tasks are often related to the PUFA's ability to combine with oxygen via its double bond.
The molecules of omega 3 fatty acids all have their first double bond starting at the third carbon atom from the methyl group.
Learn more about the nature of omega 3 fatty acids
Polyunsaturated fatty acids (PUFAs)
Because omega 3 fatty acids and omega 6 fatty acids have more than one double bond they are known as polyunsaturated fatty acids (PUFAs). PUFAs acquire more double bonds - and hence become more unsaturated - with each step or series of steps along the metabolic pathway.
Incorporation and transformation into other molecules
PUFAs are components of phospholipids, which are constituents of cell membranes, where they perform several important functions including facilitation of nutrient transport into the cell.
The PUFAs that have 20 carbon atoms, including the omega 3 (n
-3) PUFA EPA, are precursors to eicosanoids. These important enzyme-like compounds regulate many vital metabolic processes.
EPA and DHA are precursors to anti-inflammatory lipids called resolvins and protectins.
Fatty acids are also components of triglycerides, which are stored as body fat for insulation and for generating energy.
Competition between n-3 PUFAs and n-6 PUFAs
The areas of competition between n
-3 PUFAs and n
-6 PUFAs lie at the core of the important n
-3 to n
-6 intake ratio theme.
Because both families of PUFAs have similar metabolic pathways they compete for limited supplies of desaturase and elongase enzymes.
These enzymes are believed to favor ALA over LA. However, if LA consumption is very high compared with ALA, the n
-3 metabolic pathway may be deprived of the enzymes needed to make EPA and DHA.
-3 PUFAs also compete with n
-6 PUFAs for inclusion in phospholipid synthesis.
The sequence of events involved in manufacturing the derivative PUFAs from the parent EFA is known as a metabolic pathway.
The metabolic pathways for ALA and LA require enzymes, including those of the desaturase and elongase families. As their names suggest, these enzymes make fatty acid molecules less saturated (by adding more hydrogen double bonds) and longer (by extending the carbon chain). This changes their chemical properties, allowing them to perform different physiological functions from their parent.
The principal products of the n
-3 metabolic pathway are EPA and DHA, both of which can also be obtained by eating fish and algae.
The effective conversion rate for ALA into EPA and DHA has proved very difficult to determine. It appears to be highly variable and to depend on several factors. The quantity of EPA that can be made in the body from ALA is believed to be fairly small and the amount of DHA considerably smaller.
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