The short version
- In a trial in 72 volunteers taking about 3.3g of EPA plus DHA daily for two weeks, bioavailability was 124% of natural fish oil for re-esterified triglycerides, 91% for free fatty acids and 73% for ethyl esters.
- In a crossover trial in 24 healthy adults, krill oil at 600mg of n-3 PUFA raised plasma and red blood cell omega-3 concentrations and the omega-3 index more than an equal dose from fish oil.
- Algal oil capsules supplying 600mg of DHA daily were bioequivalent to assayed portions of cooked salmon over two weeks in 32 adults, with DHA rising about 80% in plasma phospholipids in both groups.
- Of 32 fish oil supplements analysed in New Zealand, only 3 met or exceeded labelled EPA and DHA content, 83% exceeded recommended peroxide values, and only 8% met all international oxidation recommendations.
- A separate accredited-laboratory analysis of ten Australian and New Zealand products found all met label claims and peroxide standards, so product quality varies more by manufacturer and market than by chemical format.
Turn over four fish oil bottles and you will find four different chemistries described in small print: natural triglyceride, re-esterified triglyceride, ethyl ester, and phospholipid. A fifth option, algal oil, skips fish entirely. The marketing around this is unusually confident. The data is narrower than the marketing but not empty, so it is worth laying out precisely.
The one trial that compared the formats directly
Seventy-two volunteers took roughly 3.3g of EPA plus DHA daily for two weeks, in one of several formats, with increases in EPA and DHA measured in fasting serum triglycerides, cholesterol esters and phospholipids. Natural fish body oil was the reference point at 100%.
- Re-esterified triglycerides: 124% of natural fish oil.
- Free fatty acids: 91%, not significantly different from natural triglycerides.
- Ethyl esters: 73%.
That is a 51-percentage-point spread between the best and worst format at the same nominal dose, over two weeks. It is one trial, in 72 people, on a short timescale, measuring blood levels rather than any clinical outcome — all of which should temper how much weight it carries. But it is the cleanest head-to-head available, and it is the reason the triglyceride form commands a premium.
Worth understanding why. Ethyl esters are what you get when fish oil is concentrated: the glycerol backbone is replaced with ethanol so the EPA and DHA can be purified to higher percentages. Re-esterified triglyceride products then convert them back, which costs money. A high-concentration ethyl ester capsule is not a defective product — it is a cheaper route to a high dose, absorbed somewhat less efficiently.
Krill oil
Krill delivers omega-3s bound to phospholipids rather than triglycerides, and the claim is better incorporation. A crossover trial in 24 healthy volunteers gave krill oil or fish oil, each supplying 600mg of n-3 PUFA, for four weeks with eight-week washouts. Krill raised plasma and red blood cell n-3 concentrations more than fish oil (P = 0.0043 and P = 0.0011) and produced a higher omega-3 index (P = 0.0143). Triglycerides and HDL did not change on either.
Twenty-four people, four weeks, one outcome that is a blood marker. Krill also costs several times more per gram of EPA and DHA, and the dose per capsule is usually much lower. If you are paying a premium for better absorption of a smaller dose, do the arithmetic on cost per gram of actual EPA plus DHA before deciding you have upgraded.
Algal oil, which is the underrated one
A randomised parallel-group study compared 600mg of DHA a day from algal oil capsules against assayed portions of cooked salmon in 32 healthy adults over two weeks. DHA rose about 80% in plasma phospholipids and about 25% in erythrocytes in both groups, and the changes were similar between them. The authors concluded the two were bioequivalent as DHA sources.
Algal oil is where the DHA in fish comes from in the first place — fish concentrate it from microalgae. It has no fish taste, no fish burps, and no fishing supply chain. Most algal products are DHA-heavy and lower in EPA, which matters if EPA is what you are after, and they are typically more expensive per gram. For anyone vegetarian or vegan, this is the format, and it is not a compromise.
The variable that beats all of the above
Format arguments assume the bottle contains what it says. When 32 encapsulated fish oil supplements sold in New Zealand were analysed, only 3 contained EPA and DHA at or above the labelled amount, and most (69%) contained less than 67% of it. Oxidation markers were worse: 83% exceeded recommended peroxide values, 50% exceeded recommended total oxidation values, and only 8% met all the international recommendations. Best-before date, cost, country of origin and exclusivity were all poor predictors of quality.
A later Australian and New Zealand analysis of ten products, using an accredited laboratory, found the opposite — all ten met or exceeded label claims and all met the peroxide standard — so this is not a settled picture, and one of those papers had industry involvement. Read together, the honest conclusion is that quality varies by product and by market far more than it varies by chemical format.
Which means a well-made ethyl ester product beats a badly made triglyceride one, comfortably. Oxidation is also the reason expiry dates and how supplements are stored matter more for fish oil than for almost anything else on your shelf.
What we'd actually tell you
Compare products on cost per gram of combined EPA and DHA, not per capsule and not per milligram of "fish oil". Read the panel: a 1,000mg capsule frequently contains 300mg of actives.
Prefer a triglyceride form if the price gap is small, choose algal if you do not eat fish, and do not pay a large premium for krill unless you have run the cost-per-gram numbers and still like them. Then check the freshness evidence — smell the contents of a capsule if you can, and treat a strongly rancid one as a return rather than a supplement. A brand that publishes third-party testing on oxidation markers is telling you something the front label never will. And if you are looking for somewhere to cut your stack, a format upgrade is a better thing to drop than the dose.
Good questions
Is triglyceride fish oil worth paying more for than ethyl ester?
If the price gap is modest, yes; if it is large, not necessarily. The head-to-head trial found re-esterified triglycerides absorbed at 124% of natural fish oil and ethyl esters at 73% over two weeks. That is a real difference in a single trial measuring blood levels. It is smaller than the difference between a fresh product and a rancid one.
Is krill oil better than fish oil?
It absorbed better per gram in a small crossover trial, and it costs considerably more per gram of EPA and DHA. Krill raised the omega-3 index more than an equal 600mg dose of fish oil in 24 people over four weeks. Whether that is worth several times the price depends on the cost-per-gram arithmetic, which most krill packaging makes difficult on purpose.
Can vegetarians get EPA and DHA without fish?
Yes, from algal oil, and it is not a second-best option. Algal DHA capsules were bioequivalent to cooked salmon in a randomised comparison. Fish get their DHA from microalgae in the first place. The practical caveats are that most algal products are DHA-heavy with less EPA, and they cost more per gram.
How do I tell if my fish oil has gone rancid?
Smell and taste are surprisingly good detectors. Fresh fish oil smells faintly of the sea; oxidised oil smells sharply fishy or like old paint, and repeated fishy burps often mean the oil, not you. Analyses have found a majority of products on some shelves exceeding recommended oxidation limits, so this is worth checking rather than assuming.
What dose of omega-3 should I actually be comparing?
Combined EPA plus DHA, per day, per dollar. The number on the front of the bottle is usually total fish oil, and a 1,000mg capsule commonly contains around 300mg of actives. Two products with identical front labels can differ threefold on the measure that matters. Turn the bottle over before you compare prices.
Does it matter whether the label says fish oil or omega-3?
Less than what the supplement facts panel says. Neither phrase tells you the format, the concentration or the freshness. Read the EPA and DHA lines, look for the chemical form, and if the brand publishes oxidation data, that tells you more than any of the words on the front.
Sources
- Dyerberg J, Madsen P, Møller JM, Aardestrup I, Schmidt EB. Bioavailability of marine n-3 fatty acid formulations. Prostaglandins Leukot Essent Fatty Acids, 2010. View study
- Ramprasath VR, Eyal I, Zchut S, Jones PJ. Enhanced increase of omega-3 index in healthy individuals with response to 4-week n-3 fatty acid supplementation from krill oil versus fish oil. Lipids Health Dis, 2013. View study
- Arterburn LM, Oken HA, Bailey Hall E, Hamersley J, Kuratko CN, Hoffman JP. Algal-oil capsules and cooked salmon: nutritionally equivalent sources of docosahexaenoic acid. J Am Diet Assoc, 2008. View study
- Albert BB, Derraik JG, Cameron-Smith D, et al. Fish oil supplements in New Zealand are highly oxidised and do not meet label content of n-3 PUFA. Sci Rep, 2015. View study
- Nichols PD, Dogan L, Sinclair A. Australian and New Zealand Fish Oil Products in 2016 Meet Label Omega-3 Claims and Are Not Oxidized. Nutrients, 2016. View study
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.
