HPC › Nutrition › Glossary
Omega-3 Fatty Acids are a family of polyunsaturated fats characterised by a double bond at the third carbon from the methyl end of the chain. The three nutritionally significant members are ALA, EPA, and DHA. EPA drives anti-inflammatory eicosanoid signalling; DHA is the dominant structural fat in neuronal membranes and the retina, influencing membrane fluidity and receptor function.
ALA, found in flaxseed and walnuts, is technically essential but converts to EPA at under 10% efficiency and to DHA at below 1%, making dietary EPA and DHA critical.
How it works
The three primary omega-3 fatty acids differ substantially in their metabolic roles. ALA (alpha-linolenic acid) is the plant-derived form, present in flaxseed, chia, and walnuts. It is classified as essential because the human body cannot synthesise it; conversion to the longer-chain forms is poor: less than 10% of ALA is elongated to EPA, and less than 1% reaches DHA 1. This conversion bottleneck means that reliance on plant sources alone leaves most people deficient in the marine-chain forms that drive the clinically documented benefits.
EPA (eicosapentaenoic acid, 20 carbons) is the principal precursor to anti-inflammatory eicosanoids. It competes with arachidonic acid, the dominant omega-6 fatty acid, for cyclooxygenase and lipoxygenase enzymes, producing Series-3 prostaglandins and Series-5 leukotrienes that are substantially less pro-inflammatory than their omega-6-derived counterparts. EPA also generates resolvins of the E-series, which actively terminate inflammatory cascades rather than merely suppressing them 3. At the cellular level, omega-3s disrupt pro-inflammatory lipid rafts and suppress NF-kB activation, reducing expression of cytokines including IL-6 and TNF-alpha 3.
DHA (docosahexaenoic acid, 22 carbons) serves an entirely different function. It constitutes approximately 15-20% of total fatty acids in the cerebral cortex and is the dominant structural lipid in retinal photoreceptor outer-segment membranes, directly governing membrane fluidity and the speed of signal transduction 4. Where EPA can be understood as the signalling layer, modulating the inflammatory response, DHA is the physical substrate: the membrane architecture upon which neuronal function depends.
Example
An endurance athlete consuming a well-rounded diet relies heavily on oily fish and occasionally supplements with fish oil during heavy training blocks. When a coach substitutes flaxseed oil for the fish oil, reasoning that both are omega-3 sources, the athlete's EPA and DHA intake drops sharply: ALA converts to DHA at below 1% efficiency. The anti-inflammatory and recovery benefits the athlete expected do not materialise.
Not all omega-3 sources are equivalent: the source determines whether you receive the marine-chain forms that carry the research-backed benefits.
Why it matters
The cardiovascular evidence is substantial. EPA and DHA supplementation reduces fasting plasma triglycerides, lowers resting heart rate, and decreases blood pressure, with effects that scale with dose 2. The clinical relevance is greatest in individuals with elevated cardiovascular risk, but the underlying mechanisms, including reduced platelet aggregation, improved endothelial function, and lower circulating inflammatory cytokines, operate across the risk spectrum.
For cognitive performance and long-term brain health, the Omega-3 Index (erythrocyte EPA+DHA as a percentage of total fatty acids) offers a more actionable biomarker than dietary recall alone. A lower index correlates with reduced brain volume, accelerated cognitive decline, and elevated risk of ischaemic stroke 4. Western diets maintain an omega-6 to omega-3 ratio of approximately 15:1, far above the evolutionary baseline of roughly 1:1 1. This chronic imbalance sets the inflammatory tone of the body's most lipid-rich organ.
What is the difference between EPA and DHA?+
EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are both marine-chain omega-3s but serve different roles. EPA is the primary driver of anti-inflammatory eicosanoid synthesis, generating resolvins that actively resolve inflammation {{cite:10.1042/bst20160474}}. DHA is a structural fat: it constitutes roughly 15-20% of fatty acids in the cerebral cortex and governs neuronal membrane fluidity {{cite:10.3390/nu13041074}}.
Can omega-3 fatty acids reduce inflammation?+
Yes. EPA competes with arachidonic acid for cyclooxygenase and lipoxygenase enzymes, producing less pro-inflammatory eicosanoids and generating resolvins that actively terminate inflammatory cascades {{cite:10.1042/bst20160474}}. Omega-3s also suppress NF-kB, reducing cytokines including IL-6 and TNF-alpha. The effect is dose-dependent and most pronounced when the overall dietary omega-6:omega-3 ratio is also reduced.
What are the best food sources of omega-3 fatty acids?+
Fatty fish (salmon, mackerel, sardines, anchovies) provide the most bioavailable EPA and DHA. Two servings per week supply approximately 500 mg EPA+DHA daily, the minimum associated with cardiovascular benefit {{cite:10.1016/j.jacc.2011.06.063}}. For non-fish-eaters, algal oil is the only plant-based source of pre-formed DHA; flaxseed and walnuts supply ALA, which converts to DHA at below 1% efficiency.
Do omega-3 supplements help the heart?+
EPA and DHA supplementation reduces fasting triglycerides, lowers resting heart rate, and decreases blood pressure in a dose-dependent manner {{cite:10.1016/j.jacc.2011.06.063}}. The benefit is greatest in people with elevated cardiovascular risk. Dietary sources, specifically fatty fish twice per week, achieve comparable plasma levels and carry additional nutritional co-factors.
