Why Omega-3s Are Different From Other Fats
Omega-3 fatty acids are polyunsaturated fats that are essential — meaning the body cannot synthesise them and must obtain them from diet or supplements. The three main types are:
- ALA (alpha-linolenic acid) — found in flaxseed, chia, walnuts. The plant-based omega-3. The body converts a small fraction to EPA and DHA, but the conversion rate is typically less than 5%.
- EPA (eicosapentaenoic acid) — primarily anti-inflammatory. Found in oily fish and fish oil supplements.
- DHA (docosahexaenoic acid) — structural component of neuronal membranes, the retina, and sperm. Found in oily fish; algae is the vegan source.
For most evidence-backed health benefits, EPA and DHA are the relevant compounds — not ALA. Plant-based omega-3 sources (flaxseed, hemp, walnut) provide ALA but insufficient EPA/DHA for most people unless consuming large quantities.
Omega-3 for Brain Health
DHA is a structural component of neuronal cell membranes — it makes up approximately 40% of the polyunsaturated fatty acids in the brain. Without adequate DHA, membrane fluidity is impaired, affecting signal transmission between neurons. EPA influences inflammatory pathways in the brain and is the more relevant compound for mood.
Evidence for brain-related benefits:
- Depression: A 2019 meta-analysis of 26 RCTs found omega-3 supplementation (particularly EPA-dominant formulations) significantly improved depression symptoms compared to placebo. EPA appears more effective than DHA for mood.
- Cognitive decline: Multiple observational studies show higher omega-3 intake is associated with lower dementia risk. Supplementation trials show mixed results but consistent benefit in people with low baseline intake.
- ADHD in children: Meta-analyses show omega-3 supplementation produces modest but significant improvements in attention and hyperactivity symptoms.
- Infant brain development: DHA is essential for foetal brain development — supplementation during pregnancy is well-evidenced for neonatal cognitive outcomes.
Omega-3 for Cardiovascular Health
Omega-3s were first studied in the 1970s after researchers noted extremely low rates of cardiovascular disease in Greenlandic Inuit populations who consumed very high quantities of oily fish. Mechanisms include:
- Reducing triglycerides (blood fats) — one of the most consistent findings across hundreds of trials
- Reducing inflammation (lower CRP, IL-6)
- Mild blood pressure lowering effect
- Anti-arrhythmic effects
High-dose EPA (as prescription Vascepa/icosapentaenoic acid, 4g/day) has been shown in a large RCT to significantly reduce cardiovascular events in high-risk patients on statins. At normal supplement doses, the cardiovascular benefits are more modest but still meaningful.
Omega-3 for Inflammation and Joint Health
EPA and DHA are precursors to anti-inflammatory eicosanoids (resolvins, protectins) that actively resolve inflammation. Multiple RCTs show fish oil supplementation reduces joint pain and stiffness in rheumatoid arthritis — some trials allowing patients to reduce NSAID use. A 2012 meta-analysis confirmed significant reduction in joint pain, morning stiffness, and NSAID use with omega-3 supplementation.
How Much Omega-3 Do You Need?
UK dietary guidelines suggest consuming 2 portions of oily fish per week (salmon, mackerel, sardines, herring, anchovies), providing approximately 3–4g combined EPA+DHA weekly. Most people fall significantly short of this. For supplementation:
- General health: 500mg–1g combined EPA+DHA daily
- Anti-inflammatory: 2–3g combined EPA+DHA daily
- Depression: 1–2g EPA-dominant formula (EPA:DHA ratio of at least 2:1)
- Triglycerides: 2–4g daily (prescription doses for severe hypertriglyceridaemia)
What to Look For in an Omega-3 Supplement
- EPA+DHA content — check the total, not just "fish oil" dose. A 1,000mg fish oil capsule may contain only 300mg EPA+DHA.
- Triglyceride vs ethyl ester form — triglyceride form is better absorbed and doesn't require fat for absorption. Most budget supplements use ethyl ester form.
- Freshness/oxidation — rancid fish oil is less effective and can be harmful. Look for TOTOX value below 26 and buy from brands with third-party testing.
- Vegan option — algae oil provides DHA and EPA (the source fish get omega-3 from in the first place) without the sustainability concerns of fish.
Bottom Line
EPA and DHA are among the most evidence-backed supplements for brain health, cardiovascular protection, inflammation, and joint pain. Most UK adults get insufficient omega-3 from diet alone. Aim for at least 500mg combined EPA+DHA daily from a quality triglyceride-form supplement or algae oil. Higher doses (2–3g) are appropriate for those targeting anti-inflammatory or mood benefits.