Omega-3 fatty acids are made up of carbon chains of varying lengths with three or more unsaturated double bonds.
Plant-derived alpha-linolenic acid (ALA) – contained in flaxseed, certain rapeseed varieties and in walnuts – has 18 carbon atoms and three unsaturated double bonds. ALA belongs to the short-chain omega-3 fatty acids.
Exclusively found in fish and algae, the long-chain omega-3 fatty acids EPA and DHA are made up of 20 or 22 carbon atoms with 4 to 6 double bonds. DHA has the longest carbon chain with the highest number of double bonds. So DHA has the highest level of bioactivity.