Guide
Types of fish oil compared: triglyceride, ethyl ester and more
A dose-matched trial found no significant absorption difference between fish oil ethyl ester, triglyceride and krill oil. Here's what each form is, and where our label's gaps sit.
Fish oil is sold in a handful of different chemical forms — natural triglyceride, ethyl ester, re-esterified triglyceride, and free fatty acid — plus krill oil, which binds its omega-3s to phospholipids instead. When a trial matched the EPA and DHA dose exactly across forms, it found no statistically significant difference in blood levels. There isn't a settled "best" form; the honest answer depends on what you're weighing form against.
| Form | What it is | Where it shows up |
|---|---|---|
| Triglyceride (natural) | The form omega-3s take naturally in fish; oil is extracted and concentrated but the fatty acids stay attached to a glycerol backbone | Common in standard fish oil softgels |
| Ethyl ester | The fatty acid is bonded to an ethanol molecule instead, a step used to concentrate EPA and DHA to a higher percentage | Common in higher-concentration and some prescription products |
| Re-esterified triglyceride | Ethyl esters converted back to a triglyceride form after concentration, combining higher concentration with the natural fat structure | A smaller, usually pricier category |
| Free fatty acid | The fatty acid isn't attached to anything; the most bioavailable form in older single-dose research, and the least common commercially | Rare in mainstream softgels |
| Phospholipid (krill oil) | Omega-3s bound to phospholipids rather than a glycerol backbone or ethanol; also naturally contains astaxanthin | Krill oil specifically — see fish oil vs krill oil |
What the research says when the dose is matched
An older single-dose study in 8 men, done without co-ingested food, found the free fatty acid form absorbed best, the natural triglyceride form somewhat less well, and ethyl esters substantially worse — about a fifth as well as the free fatty acid form. That result helped establish ethyl esters' reputation as the weaker absorber. A more recent, better-designed trial told a different story: when 66 healthy adults were given a matched 1.3 g/day dose of EPA and DHA as fish oil ethyl ester, fish oil triglyceride, or krill oil for four weeks, there was no statistically significant difference in blood EPA+DHA levels between the three — bioavailability differed by less than 24%. That trial was funded by a supplement ingredient manufacturer, which is worth knowing when weighing its conclusion. Taken together: the biggest documented absorption gap (ethyl ester without food) mostly disappears once food and dose are properly matched.
Where our label sits
Electric Tiger Omega-3's panel lists the ingredient as "fish oil concentrate" — 1,000 mg per softgel, providing 180 mg EPA and 120 mg DHA — without stating which specific ester form it is. That's a real gap in what the label tells you, and it's a fair question to ask any fish oil brand, ours included, if the distinction matters to you.
Cod liver oil is a different product
Cod liver oil is fish oil sourced specifically from cod liver, and unlike a fish oil concentrate, it naturally carries meaningful amounts of vitamin A and vitamin D alongside EPA and DHA. That means its labeled serving size is often set by the vitamin A or D content, not just the omega-3 amount — worth checking against its own label, especially if you're also taking a separate vitamin A or D supplement, rather than assuming it's interchangeable with a plain fish oil concentrate.
Questions people ask
What is the best form of omega-3?
There isn't a form that a dose-matched trial has shown outperforms the others in blood levels — fish oil ethyl ester, fish oil triglyceride and krill oil came out statistically similar in the trial above. Cost, capsule size, allergen source and personal tolerance (fishy aftertaste, capsule size) are more likely to be the deciding factors than absorption at a matched dose.
What are the different types of omega-3 products?
Beyond the fish oil chemical forms above, omega-3 products also differ by source: fish oil (EPA and DHA from fatty fish), krill oil (phospholipid-bound EPA and DHA plus astaxanthin), cod liver oil (fish oil plus vitamin A and D), and algae oil (a vegan DHA source, typically with little or no EPA). Ours is a fish oil concentrate — EPA and DHA only, no added vitamin A, D or algae oil.
Sources
- Lawson LD, Hughes BG. Human absorption of fish oil fatty acids as triacylglycerols, free acids, or ethyl esters. PMID 3358766.
- Yurko-Mauro K, et al. Similar EPA and DHA plasma levels achieved with fish oil or krill oil in a randomized double-blind four-week bioavailability study. PMID 26328782.
- Electric Tiger Omega-3 Supplement Facts: product page.
Related reading: how to choose a good fish oil, fish oil vs krill oil, and what is fish oil.
Sources
- Human absorption of fish oil fatty acids as triacylglycerols, free acids, or ethyl esters In a small single-dose trial without food, free fatty acid fish oil was absorbed best, the natural triglyceride form somewhat less well, and the ethyl ester form substantially worse — about a fifth as well as the free acid form.
- Similar eicosapentaenoic acid and docosahexaenoic acid plasma levels achieved with fish oil or krill oil in a randomized double-blind four-week bioavailability study When doses of EPA and DHA were matched exactly, a four-week trial in 66 healthy adults found no statistically significant difference in blood levels between ethyl ester fish oil, triglyceride fish oil, and krill oil; this trial was funded by a supplement ingredient manufacturer.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
