EPA/DHA ratio and inflammatory conditions
There is a plethora of fish oils with varying ratios of EPA and DHA long-chain omega-3 fatty acids, with numerous applications. When addressing specific ailments or conditions related to inflammation, however, the ratio of EPA to DHA becomes very important and can determine the efficacy of any outcome, as their physiological actions are quite distinct.
Whilst these fatty acids are both essential for good health, their structures are very similar and they compete for binding sites as well as essential enzymes. EPA and DHA are found together in most supplements, but their competitive relationship means that the beneficial actions are derived from any excess EPA or DHA, once any equal quantities of EPA and DHA have effectively cancelled each other out. Many recent clinical studies, especially those focusing on the benefits of omega-3 in inflammatory conditions, have investigated the actions of pure EPA owing to its dual protection against excess inflammation in the body: EPA displaces the omega-6 AA content of cell membranes, reducing the inflammatory products that can be produced from AA – effectively regulating inflammatory pathways – and it also enhances the production of anti-inflammatory products that are directly converted from EPA. Supplementing the diet with pure EPA without DHA therefore maximises the beneficial actions of this important nutrient for inflammatory conditions because it is unopposed by the competing actions of DHA for binding sites and enzymes.
Whilst many studies have attempted to treat such conditions with EPA and DHA oils, the outcomes have been varied and often contradictory. This has led researchers to investigate the individual actions of the two fatty acids in numerous conditions where deficiencies are known to be key players in their symptoms. As such, it is suggested by a number of researchers that due to similarities in structure, EPA and DHA compete 1:1 for binding sites and that the DHA within a treatment regime appears to ‘block’ the therapeutic actions of EPA (Martins 2009; Bloch & Qawasmi et al, 2011; Sublette et al, 2011). In contrast, using pure ethyl-EPA has routinely been shown to increases the efficacy of a treatment regime and it is increasingly recognised that the absence  of DHA, and therefore absence of competition between EPA and DHA for biological sites of action, is responsible for the outcomes seen in such trials. Therefore oils containing DHA may not be suitable for the treatment of a variety of conditions and may explain the lack of efficacy with use of generic fish oils.
Bloch MH & Qawasmi A. (2011) Omega-3 fatty acid supplementation for the treatment of children with attention-deficit/hyperactivity disorder symptomatology: systematic review and meta-analysis. Journal of the American Academy of Child Adolescent Psychiatry 50:991-1000.
Martins JG. (2009) EPA but not DHA appears to be responsible for the efficacy of omega-3 long-chain polyunsaturated fatty acid supplementation in depression: evidence from a meta-analysis of randomized controlled trials. Journal of the American College of Nutrition 28: 525-42. Review.
Sublette ME, Ellis SP, Geant AL, Mann JJ. (2011) Meta-analysis of the effects of eicosapentaenoic acid (EPA) in clinical trials in depression. Journal of Clinical Psychiatry 72: 1577-84.