There are three essential omega-3 fatty acids which have been identified as important to our health. These fatty acids are: ALA (alpha-linolenic acid), EPA (eicosapentaenoic acid), and DHA (docosahexaenoic acid). ALA is an omega-3 fatty acid that is synthesized in plants. EPA and DHA are found in relatively large quantities in some of the more oily fish, in lesser quantities in other seafood, and in even lesser quantities in the flesh of animals.
ALA must be obtained by the ingestion of plant material; our bodies cannot synthesize it from other substances, therefore ALA is an essential fatty acid. It is possible for the human body to convert ALA into EPA and DHA, but we do not seem to convert a very large percentage of the ALA to these fatty acids. Therefore it appears very possible to suffer from a deficiency of EPA and DHA despite a substantial intake of ALA, and so EPA and DHA are also considered essential fatty acids.
The media and many food manufacturers often treat ALA, DHA, and EPA as if they were interchangeable. For instance, I have seen claims that walnut oil has more omega-3’s than salmon. If you are looking at omega-3 fatty acids in a general sense this is a true statement. However, the omega-3 fatty acid in walnuts is ALA while the omega-3 fatty acids in salmon are DHA and EPA. These three serve different functions in the body and so are not interchangeable. As I stated above, our bodies are capable of converting small percentages of ALA to EPA and even smaller percentages to DHA, but it is difficult to consume enough ALA to meet your daily requirement of DHA and EPA (although this may be possible.) At this point it seems to me that it is wise to get omega-3 fatty acids from both sources.
In research studies increasing ALA has demonstrated the ability to reduce inflammation and C-reactive protein which are early warning signs of cardiovascular disease. (2) ALA has also shown some ability to help lower cholesterol levels (specifically LDL and vLDL). (3)
Much research has been done on EPA and DHA.
- These two omega-3 fatty acids have been shown to play a significant role in brain development in babies and in preventing cognitive decline in older people. (4)
- They have also been shown to significantly lower the risk of cardiovascular disease. (5)
- Individually or in combination these two fatty acids have also been shown to lower triglycerides, decrease clumping of platelets, and decrease inflammation. (6)(9)
- Some studies seem to indicate some degree of cancer protection provided by EPA or DHA, but other studies contradict this, so the jury is still out.
- DHA itself is involved in memory formation, the protection of nerve cells from oxidation, and in retina development and maintenance. (7)
- An increase in the intake of DHA also seems to be related to a decreased risk of macular degeneration. (8)
These are only a sample of the studies which have been done on DHA and EPA. I am convinced these omega-3 fatty acids along with ALA are critical for our health and that the average American diet does not provide anywhere near the amount needed.
For more information see:
(2) Dietary α-linolenicacid decreases C-reactive protein, serum amyloid A and interleukin-6 in dyslipidaemic patients. Authors: Loukianos S. Rallidisa, Georgios Paschosb, Georgios K. Liakosc, Aggeliki H. Velissaridouc, Georgios Anastasiadisd, Antonis Zampelasb
(3) Dietary alpha-linolenic acid is as effective as oleic acid and linoleic acid in lowering blood cholesterol in normolipidemic men. Authors: JK Chan, VM Bruce and BE McDonald
(4) Nutrition in Brain Development and Aging: Role of Essential Fatty Acids. Authors: Ricardo Uauy MD, PhD*, Alan D. Dangour PhD
(5) Fish Consumption, Fish Oil, Omega-3 Fatty Acids, and Cardiovascular Disease. Authors: Penny M. Kris-Etherton, PhD, RD; William S. Harris, PhD; Lawrence J. Appel, MD, MPH;
(6) n–3 Fatty acids and cardiovascular disease. Author: Jan L Breslow
(8) Prospective study of dietary fat and the risk of age-related macular degeneration. Authors: Eunyoung Cho, Shirley Hung, Walter C Willett, Donna Spiegelman, Eric B Rimm, Johanna M Seddon, Graham A Colditz and Susan E Hankinson
(9) Dietary docosahexaenoic and eicosapentaenoic acid: Emerging mediators of inflammation. Authors: Robert S. Chapkin, Wooki Kim, Joanne R. Lupton, David N. McMurray