Krill oil vs fish oil: what actually reaches your cells

Walk the omega-3 aisle and every front label shouts a milligram number. It is the wrong number to be looking at. What matters for your body is not how much EPA and DHA a capsule contains, but how much actually crosses from your gut into your bloodstream — and on that measure, the humble question of how the oil is packaged does a surprising amount of the work.

The number that matters is absorption

EPA and DHA are the two long-chain omega-3s that the research is really about. Both krill oil and fish oil deliver them. The difference is the carrier molecule each omega-3 is attached to, and that carrier turns out to be the hinge the whole comparison swings on.

Standard fish oil comes in one of two forms. In its natural triglyceride form (and the "re-esterified" triglyceride form used in premium products) the omega-3s sit on the same backbone they occupy in the fish itself. In the cheaper, more concentrated ethyl-ester form, created during processing, they are attached to an alcohol instead. Krill oil is different again: a meaningful share of its omega-3s are bound to phospholipids — the very class of molecule your own cell membranes are built from.

Why the carrier changes your real dose

Human absorption studies have compared these forms directly for decades, and the pattern is consistent. Ethyl esters are the fussiest: they depend heavily on being taken alongside dietary fat, and on an empty stomach their absorption can fall by around half compared with taking them with a fatty meal.^1,2 Triglyceride forms absorb more readily and more reliably,³ and phospholipid-bound omega-3s from krill are absorbed about as easily as the fats in food.^4,5

Krill oil (phospholipid)best absorbed

Re-esterified triglyceride fish oilhigh

Natural triglyceride fish oilhigh

Ethyl-ester fish oil, with foodmoderate

Ethyl-ester fish oil, empty stomachlowest

This is why two products showing the same milligrams can deliver quite different amounts to your blood. A cheap ethyl-ester capsule swallowed with a glass of water is close to the worst case; a phospholipid or triglyceride form taken with a meal is close to the best.

Krill's head start

The clearest way to see the difference is to measure what actually ends up in the body. In a head-to-head trial, four weeks of krill oil raised the Omega-3 Index — the share of EPA and DHA in red blood cell membranes — more than the same dose of omega-3s from fish oil.⁶ Other work has found krill can match fish oil's effects at a lower labelled dose of EPA and DHA, precisely because more of it is absorbed.^5,7

Krill oilgreater rise

Fish oil (matched EPA+DHA)smaller rise

The two passengers fish oil doesn't carry

Krill oil also arrives with company that plain fish oil lacks. The first is astaxanthin, the red carotenoid that gives krill and salmon their colour and one of the more potent antioxidants in nature.⁸ It does a quiet but useful job: it helps protect the delicate omega-3s from oxidising, which is a large part of why krill so rarely causes the fishy aftertaste and repeat that older fish-oil capsules were notorious for.

The second is choline, an essential nutrient that most diets fall short of, present in krill as phosphatidylcholine. It is the same nutrient your liver and brain rely on — a genuine bonus rather than a marketing flourish.

So which should you take?

Food first, always: if you eat oily fish two or three times a week, you may not need either supplement, and our calculator will tell you as much. If you do supplement, the honest ranking is not about the biggest number on the label. It is about matching the dose you actually absorb to your goal, favouring a well-absorbed form, and — whatever you choose — taking it with a meal that contains some fat.

Fish oil's advantage is cost per milligram; if you buy a triglyceride form and take it with dinner, it does the job. Krill's advantage is that it removes the variables for you: a well-absorbed phospholipid form, gentle on the stomach, with astaxanthin and choline along for the ride — at a higher price per milligram, and usually a lower milligram count per capsule, which is the fair trade to keep in mind.

To see what your own routine really delivers — form, meal timing and the fish you already eat, all accounted for — run the numbers through our omega-3 dosage calculator. And if krill is the form you want, AstaKrill is built around exactly the advantages above.

References

Peer-reviewed sources for the mechanisms and findings above, offered for further reading. Nothing here is medical advice or a claim to treat, cure or prevent any condition.

1. Lawson LD, Hughes BG. Human absorption of fish oil fatty acids as triacylglycerols, free acids, or ethyl esters. Biochem Biophys Res Commun. 1988;152(1):328–335.
2. Schuchardt JP, Hahn A. Bioavailability of long-chain omega-3 fatty acids. Prostaglandins Leukot Essent Fatty Acids. 2013;89(1):1–8.
3. Dyerberg J, Madsen P, Møller JM, Aardestrup I, Schmidt EB. Bioavailability of marine n-3 fatty acid formulations. Prostaglandins Leukot Essent Fatty Acids. 2010;83(3):137–141.
4. Köhler A, Sarkkinen E, Tapola N, Niskanen T, Bruheim I. Bioavailability of fatty acids from krill oil, krill meal and fish oil in healthy subjects — a randomized, single-dose, cross-over trial. Lipids Health Dis. 2015;14:19.
5. Ulven SM, Kirkhus B, Lamglait A, et al. Metabolic effects of krill oil are essentially similar to those of fish oil but at lower dose of EPA and DHA, in healthy volunteers. Lipids. 2011;46(1):37–46.
6. Ramprasath VR, Eyal I, Zchut S, Jones PJH. 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;12:178.
7. Maki KC, Reeves MS, Farmer M, et al. Krill oil supplementation increases plasma concentrations of eicosapentaenoic and docosahexaenoic acids in overweight and obese men and women. Nutr Res. 2009;29(9):609–615.
8. Ambati RR, Phang SM, Ravi S, Aswathanarayana RG. Astaxanthin: sources, extraction, stability, biological activities and its commercial applications — a review. Mar Drugs. 2014;12(1):128–152.