Fatty acids are building blocks in the human body, and essential in order to live a healty life. Oily fish is by far the most efficient source of these essential fatty acids.
Fatty acids are building blocks for eicosanoids, which are precursors for hormones such as prostaglandins and are involved, for example, in the formation of cell membranes, blood clotting, wound healing and inflammation. EPA and DHA are ‘essential’ because we need them to live a healthy life but cannot synthesise them effectively.
Fatty acids are based on a chain of linked carbon atoms and are classified as either saturated or unsaturated. A saturated fatty acid only has single bonds between the carbon atoms — hydrogen atoms take up all other bonds. An unsaturated fatty acid has at least one carbon-carbon double bond. Polyunsaturated fatty acids (PUFAs) have two or more double bonds in the carbon chain.
In addition to omega-3 fatty acids, you will also see references in food products to omega-6 and omega-9 fatty acids. The 3, 6 and 9 indicate where the first double bond is in the carbon atom chain, counting from the end of the carbon chain.
Saturated fats are solid at room temperature while unsaturated and polyunsaturated fats have lower melting points and are liquid at room temperature. Typically they are found in vegetable oils and fish oils, but it is the fish oils in particular that are rich in EPA and DHA.
Fatty acids are also categorised according to the length of the carbon chain. Short chain fatty acids have fewer than 20 carbon atoms in the chain while long chain fatty acids have 20 or more carbon atoms in the chain.
The omega-3 fatty acid found in vegetable sources, namely alpha-linolenic acid (ALA), is a short chain polyunsaturated fatty acid (SC-PUFA) that needs to be converted into the long chain polyunsaturated fatty acid (LC-PUFAs) EPA and DHA in the body before they can be converted into beneficial eicosanoids. Incidentally, ALA should not be confused with linoleic acid, which is an important omega-6 polyunsaturated fatty acid.
EPA can be synthesised in the human body to a limited extent from ALA, but even less is converted to DHA. Women are more able to do this than men. At best the conversion rates of omega-3 fatty acid from plants (ALA) in women are 5% converted to EPA and 1% to DHA. Thus in human nutrition, fish is an important source of pre-made long chain omega-3 fatty acids, namely EPA and DHA.