* Omega-3 fatty acids explained June 13 2012

Understanding the chemistry of the polyunsaturated Omega-3 fatty acids


Omega-3s are polyunsaturated fatty acids (PUFA), sometimes referred to as N-3 polyunsaturated. They are unsaturated, which means that some Hydrogen atoms are replaced with Carbon double bonds, thus getting rid of saturation with Hydrogen. Most of the Omega-3 fatty acids are derived in their natural state from plant and animal fats. 

Human bodies cannot create an Omega-3 double bond, in other words human bodies cannot break away two Hydrogen atoms at the third carbon atom from the end and form a double carbon bond in place of Hydrogen atoms. This is what makes Omega-3 acids essential. However, human bodies can, in a limited capacity, make some Omega-3 acids from the parent Omega-3 Alpha Linolenic Acid (18:3 N-3). 

In nature there are 11 Omega-3 acids, among them the most studies Eicosapenaenoic Acid, EPA (20:5 N-3) and Docosahexaenoic Acid, DHA (22:6, N-3), followed by Alpha Linoleic acid, ALA (18:3 N-3), and Docosapentaenoic Acid, (22:5 N-3) DPA, which started gaining interest recently. ALA, found in vegetable sources, e.g. flaxseed oil and walnuts, is considered to be a parent acid to EPA and DHA. Human bodies have an ability to enzymatically elongate ALA to longer chain Omega-3s, including EPA and DHA, but this ability is limited and restricted by a number of factors thus making ALA not a very reliable pre-cursor of EPA or DHA. 

Omega-3 fatty acids consist of Carbon (C), Hydrogen (H), and Oxygen (O) atoms. The omega 3 acids are also described as long chain polyunsaturated fatty acids:


  •     A Fatty Acid is a chain of hydrocarbons (Carbon atoms with Hydrogen atoms attached to them) with a carboxyl (COOH) group at the end,
  •     Fatty Acids are named fatty because they were first isolated from natural fats and oils, 
  •     Acids are also known as FATTY when they are not “free” (as a free floating long chain), but attached to either triglyceride or phospholipid backbone. The natural state of the fish oil is triglyceride. A triglyceride is formed by combining a glycerol with three molecules of fatty acids,
  •     The presence of the carboxyl group is what allows attachment of the acid to a triglyceride or phospholipid and leads to the name “fatty”,
  •     Long chain fatty acids. Fatty acids with a chain of more than 12 carbons are referred to as long chain. The Omega-3 acids found in the fish oil typically have chains of 16 and more Carbon atoms,
  •     In many molecules in nature, Carbon atoms in a Carbon chain are bound to each other by a single bond (C-C), and all other electrons bond with Hydrogen atoms , in other words, each Carbon atom has more than one Hydrogen atom attached to it, so they are said to be “saturated” with Hydrogen,
  •     When a second electron from one Carbon atom bonds with a second electron of its neighboring Carbon atom, and thus each Carbon gets rid of 1 Hydrogen, they become Unsaturated (unsaturated with Hydrogen). It is also referred to as a Carbon double bond (C=C),
  •     When more than one Carbon is unsaturated, the acids are called poly (Greek – many) unsaturated,
  •     The fatty acids are classified by the number of Carbon atoms from the end where the first double bond (unsaturation) occurs. The nomenclature is to use Omega (the Greek letter W) to denote the last Atom. Thus Omega-3 means that the first double bond occurs at the 3rd carbon atom from the end (by the same logic, for example, Omega-6 acids have the first double bond occurring at the sixth Carbon atom from the end),
  •     Saturated acids are straight lines of Carbon.  Whenever a double bond (unsaturation) occurs, the carbon chain curves,

  •     The Omega-3 fatty acids differ by the number of carbon atoms and the number of double bonds. For example:
         -     EPA (eicosapentaenoic) acid 20:5 n-3 has 20 atoms of Carbon and 5 double bonds between carbon atoms (10 carbon atoms are not saturated with hydrogen). It has the following atoms: C20H30O2
         -     DHA (docosahexaenoic) acid 22:6 n-3 has 22 atoms of Carbon and 6 double bonds. It has the following atoms: C22H32O
    •     The naming nomenclature uses:

              -   Primarily, Greek words for numbers. E.g. EPA – eicosapentaenoic is eicosa (20 in Greek) + penta (five in Greek) + enoic (see below); DHA – docosahexaenoic is docosa (22 in Greek) + hexa (six in Greek) + enoic;
              -   Enoic refers to any unsaturated carboxylic acid. Carboxyl is a –COOH group at the end of the molecule opposite to the end, from which the first double bond is counted. And unsaturated means that it contains at least one double bond between carbon atoms.