Omega-3 fats are called that because of their structure, much like we call a floor made of marble, a marble floor, or a cup made of tin—a tin cup. Omega-3 fats are made with an omega-3 bond.
Omega-3 fats have unique properties and are found in distinctly different foods. The three most common omega-3s have long names, but can be remembered with their abbreviations: ALA for alpha-linolenic acid, EPA for eicosapentaenoic acid and DHA for docosahexaenoic acid. These three members differ in the length of the carbon chain and the number of bonds unsaturated with hydrogen (i.e. double bonds between the carbons). ALA has 18 carbons and 3 double bonds and is considered essential, i.e. the body is unable to make it so it is required in our diet. EPA 20 carbons with 5 double bonds. DHA 22 carbons and 6 double bonds. Which omega-3 fat is found in the diagram?
As of this writing, it is felt that EPA and DHA have a stronger influence on health than ALA and that although ALA can be converted to EPA and DHA, the rate is somewhat limiting. Persons wanting to get the most omega-3 influence are advised to consume some sources of EPA or DHA in addition to ALA. In general ALA is considered to be from plant based foods and EPA/DHA are from marine and animal foods. Thus sources of ALA include flaxseed, canola oil, nuts, and wheat germ, whereas EPA and DHA are in breast milk and seafoods such as salmon, sardines, herring, halibut, and tuna.
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