DEAR DR. BLONZ: Omega-3 fats are touted when naturally present, and are now being promoted when added to other foods. Are all omega-3s the same? In terms for a non-science major, please explain what the "omega" represents and why these fats are being promoted. -- J.S., Phoenix
DEAR J.S.: To explain the meaning of the "omega," we will need to consider a bit of structure. I will do my best to make it digestible.
First, we need to consider that fats and oils are similar in structure, the main difference being that fats are solid at room temperature (around 68 to 72 degrees F), while oils are liquid. For simplification, I will use the term "fat" for both. Think of fats as long chains of carbon atoms. In addition to being bound to each other, carbon atoms along the chain can have up to a pair of hydrogen atoms (though there are different rules for the carbons at the chain's end). If all the carbons in the chain have a pair of hydrogens, the fat is said to be "saturated," i.e., saturated with hydrogens.
When hydrogens are missing, adjacent carbons form a double bond. When this happens, the fatty acid is "unsaturated." When there is one double bond between adjacent carbons, the fat is "monounsaturated." Olive oil is an example of a food fat that's rich in monounsaturates. (Check tinyurl.com/zzbxdpz for a picture of a saturated and monounsaturated fatty acid.) When there is more than one double bond, the fat is "polyunsaturated." (On a side note, you may now better understand the terms "hydrogenation" and "partial hydrogenation," as these refer to the adding of hydrogens to unsaturated fats to change their performance characteristics.)
The term "omega" is used to signify the location on the carbon chain where the first double bond occurs. An omega-3 fatty acid is an unsaturated fat where the first double bond involves the third carbon atom from the end of the chain.
The significance is that our body requires omega-3 fats, but cannot make them on its own. We also require omega-6 fats, where the first double bond is on carbon number 6. Both types are considered "essential fatty acids," so we need to get them from our diet.
Linoleic acid is an omega-6 fat found in vegetable oils such as corn, safflower, soy and sesame, and it is also found in many nuts and seeds. Fish oils contain EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), both omega-3 fatty acids. Other omega-3s can be found in flaxseed, canola, soy and walnuts, but the EPA and DHA from fish are based on longer chains of carbons, which gives them unique characteristics. The body can make the longer omega-3 fats from the shorter ones, but it does not do it efficiently. This is why fish consumption is often promoted as an important part of a healthful diet.
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