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.
Learn more about Omega-3 sources.
What is an omega-3 bond?
To answer that, a little bit of information on fat structure is needed. Fat molecules are long chains of carbon atoms with hydrogen molecules attached. One end of the carbon chain has an acidic form and the other end a methyl group. The methyl group end is also called the omega end. Carbon atoms saturated with hydrogen atoms are linked by only one bond, but carbon atoms that are unsaturated with hydrogen are linked twice (said to be double bonded). Omega-3 fats, also called n-3 fats, are highly unsaturated fats, that is they are not as highly saturated with hydrogen molecules and have several double bonds. When the first double bond is on the third carbon from omega end, the fat is called an omega-3 fat. The Greek symbol for omega (the last letter in the Greek alphabet) is Ω, thus sometimes omega-3s are written as Ω-3 fat. The first double bond is on the sixth carbon from the omega end in omega-6 fats. You can see the difference in the shaded region of the omega-6 and omega-3 fat by clicking the link below.
Note how the appearance of the first double bond on the third, rather than the sixth carbon from the methyl (or omega) end actually changes the physical shape of the molecule, thus affecting how the body is able to use it. Just as changing the shape of a tool may render it useless for one type of task, it may improve its ability to do another and the outcomes will differ.