Omega-3

Also called fish oil, EPA DHA, essential fatty acids.

Dr Chad OkayFounder, Suna Health

3 min read. Updated .

Omega-3 fatty acids are a family of essential polyunsaturated fats. The body cannot make them, so you must eat them. The three main forms are EPA, DHA (both in oily fish and algae) and ALA (in flax, chia, walnuts). EPA and DHA have the strongest evidence for cardiovascular and inflammatory benefits. Aim for 2 portions of oily fish per week or supplement 250 to 500 mg of combined EPA+DHA daily.

The three forms

  • EPA (eicosapentaenoic acid): main anti-inflammatory effect.
  • DHA (docosahexaenoic acid): main neurological and visual effect.
  • ALA (alpha-linolenic acid): the plant-based parent. Body converts ~5-10% to EPA, less to DHA.

Sources

Best (EPA + DHA)

  • Salmon (1.5 g per 100 g cooked).
  • Sardines (1 g per 100 g).
  • Mackerel (2 g per 100 g).
  • Anchovies (1.5 g per 100 g).
  • Herring (1.7 g per 100 g).
  • Algae oil supplements (vegan EPA+DHA, 250 to 500 mg per capsule).

ALA only, converts poorly

  • Flaxseed (22 g ALA per 100 g).
  • Chia seeds (17 g per 100 g).
  • Walnuts (9 g per 100 g).
  • Hemp seeds (10 g per 100 g).

What omega-3 actually does

  • Reduces triglycerides (well-evidenced at 2 to 4 g/day).
  • Reduces inflammatory markers in chronically inflamed states.
  • Cardiovascular benefit: large supplement trials show little or no effect on cardiovascular or all-cause mortality; the strongest signal is triglyceride lowering.
  • Brain health: associated with lower rates of cognitive decline; causality is debated.
  • May support the gut barrier and modulate microbiome composition (mostly animal-model evidence so far).
  • Pregnancy: DHA supports fetal brain and eye development.

Dose recommendations

  • General health: 2 portions oily fish/week OR 250-500 mg EPA+DHA/day.
  • High triglycerides: 2-4 g/day under medical supervision.
  • Pregnancy: 200 mg DHA/day on top of the 250 mg EPA+DHA baseline (EFSA).
  • Vegan: algae-based EPA+DHA supplement, same target dose.
  • Don't exceed 3 g/day from supplements without medical guidance; any bleeding-risk increase appears mild and is unlikely to be clinically significant at standard doses.

What to look for in supplements

  1. Combined EPA+DHA per capsule, not just 'fish oil'. A 1000 mg fish oil capsule often has only 300 mg EPA+DHA.
  2. Triglyceride or phospholipid form (better absorbed than ethyl ester).
  3. Third-party tested for heavy metals (IFOS, USP, Friend of the Sea certifications).
  4. Stored in fridge after opening.
  5. Smell, fishy or rancid is a sign of oxidation; throw out.

Why it matters for the long run

The honest long-run picture: the strongest evidence is for what omega-3 does to blood fats, while the big supplement trials found little effect on how long people live. What holds up over decades is the food pattern rather than the capsule: two portions of oily fish a week sits inside almost every eating pattern with good long-term outcomes, and the supplement is the fallback for people who cannot get there through food.

Common questions

Can I get enough omega-3 from flax and chia alone?
Possibly enough ALA but not enough EPA and DHA. The conversion rate is too low for most people to reach useful levels. Vegans should take an algae-based supplement to get proper EPA+DHA.
Are fish oil burps dangerous?
No, just unpleasant. Caused by oil refluxing back from the stomach. Take with food, freeze the capsules, or switch to enteric-coated versions to reduce burps.
Should I worry about mercury?
Less than for unprocessed fish. Reputable supplements remove heavy metals during processing. Check for third-party purity testing on the bottle.
Will omega-3 affect my blood thinners?
At doses under 3 g/day, minimal effect. Higher doses can mildly extend bleeding time. If you are on warfarin or DOACs, check with your prescriber before starting high-dose omega-3.

Sources

Written by Dr Chad Okay. Contributor: Dr Parisah Hussain, MBChB, BSc (Hons), DRCOG, MRCGP. Last updated 15 September 2026. From Digests.

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