Why Does Whole Salmon Oil Have Less EPA and DHA Than Concentrated Fish Oil?

Because it has not been concentrated. Most fish oil on the shelf has been through an industrial refining sequence built specifically to raise the EPA and DHA figures on the label, and that sequence removes most of what surrounded those two fatty acids in the fish. Whole salmon oil skips it. The label number comes out lower, and the composition stays intact.

What is the difference between salmon oil, fatty acids, omegas, and EPA and DHA?

These four terms describe the same material at four different levels of magnification, and mixing them up is the source of most of the confusion in this category.

• Salmon oil is the whole ingredient, as it exists in the fish.
• Fatty acids are the individual molecules inside that oil. Whole salmon oil contains 21 of them.
• Omega families are how those fatty acids sort by chemical structure. The 21 fatty acids in whole salmon oil fall into six families: omega-3, 5, 6, 7, 9 and 11.
• EPA and DHA are two specific fatty acids, both of them omega-3s. They are the two most heavily studied, and on most labels they are the only two reported.

A label that lists only EPA and DHA is describing two molecules out of twenty-one. That is accurate as far as it goes. It is not the whole composition.

What does concentrating fish oil actually remove?

Concentration is a manufacturing process, not a purification step, and each stage of it takes something out.

Raising EPA and DHA above their natural proportion in the fish typically involves heat, degumming, bleaching, deodorizing, and molecular distillation — and in many products, re-esterification afterwards to reassemble the fatty acids into a triglyceride form once distillation has separated them. The purpose of the whole sequence is to isolate two fatty acids. Everything that is not those two fatty acids is, by design, reduced or removed.

Whole salmon oil is released from the fish enzymatically in a single step, and is not bleached, distilled, or re-esterified. What ends up in the softgel closely resembles what was in the fish.

That is the trade. A concentrate delivers a higher EPA and DHA number. A whole oil delivers the full composition at a lower number.

What is DPA, and why is it missing from most fish oil labels?

DPA — docosapentaenoic acid — is an omega-3 that occurs naturally in fresh fish and in whole salmon oil, and rarely appears on a concentrated fish oil label, because concentrating removes it.

DPA matters for a specific reason: the body converts a portion of it into EPA and DHA. That means some of the EPA and DHA a person ends up with was not EPA or DHA at the moment they swallowed it. No label can show that conversion. A whole oil's stated EPA and DHA figure therefore understates what the body eventually has available, by an amount the label has no way to express.

Does a lower EPA and DHA number mean less benefit?

Not necessarily, and there is now trial evidence on the question.

A 14-week randomized, active-controlled trial published in 2026 compared a minimally processed whole salmon oil ingredient against a conventional concentrated omega-3 oil in 84 healthy adults with an average age of 53. The whole oil supplied 100 mg of EPA and DHA per day. The concentrate supplied 250 mg — two and a half times as much. Both groups began at an Omega-3 Index of 5.25%.

After 14 weeks, the whole-oil group's Omega-3 Index had risen by about 12%, reaching roughly 5.9%. The concentrate group's had risen by about 7%. That is a 1.7-fold larger increase produced by 2.5 times less EPA and DHA, or a 4.3-fold larger increase measured per 100 mg of EPA and DHA consumed. Markers of inflammation, including high-sensitivity C-reactive protein, TNF-alpha and interleukin-6, also fell further in the whole-oil group.

Two caveats belong with that result. The study was funded by the manufacturer of the whole salmon oil ingredient — common in nutrition research, and worth knowing when you read it. And neither group reached an Omega-3 Index of 8%, the level most often cited as desirable. The trial measured how efficiently each oil was incorporated into cell membranes, not whether either one closes that gap.

What the trial does support is narrower and still useful: the milligram figure on the front of a bottle is not a reliable proxy for how much omega-3 ends up in a person's cells.

What should you compare instead of milligrams?

Four things carry more information than the EPA and DHA number on its own.

• Form. Whether the oil is a natural triglyceride, an ethyl ester, or a re-esterified triglyceride. These are different molecular forms produced by different amounts of processing, and they are not absorbed identically.
• Processing. How many steps sit between the fish and the softgel, and what each one takes out.
• Composition. How many fatty acids the oil actually contains, not just how many of them.
• Freshness. How quickly the fish was processed after harvest, since oil quality begins degrading from the moment the fish leaves the water.

Common questions

Is more EPA and DHA always better?

More on the label is not automatically more in your cells. A label reports what went into the capsule; what matters physiologically is how much is incorporated into your cell membranes, which is what the Omega-3 Index measures. In a 14-week head-to-head trial, a whole salmon oil supplying 100 mg of EPA and DHA daily produced a larger rise in the Omega-3 Index than a concentrate supplying 250 mg.

What is an ethyl ester, and does it matter?

An ethyl ester is a molecular form of omega-3 created during processing, not one found in fish. Concentrating fish oil converts the natural triglyceride form into ethyl esters. Some manufacturers then convert it back, producing what is called a re-esterified triglyceride. Published research has found that re-esterification is often incomplete, with only around 55 to 60% of the material fully converted in some products — so two products described the same way can differ in composition. Whole salmon oil is never converted in the first place and stays in its natural triglyceride form.

Does whole salmon oil go rancid faster because it is not deodorized?

Deodorizing removes fish flavor. It is not the step that keeps oil stable. Whole salmon oil relies instead on freshness at the source and on astaxanthin, the naturally occurring antioxidant that gives salmon its color and stays in the oil when it is not refined out.

How is whole salmon oil made?

Fresh, sashimi-grade Norwegian salmon off-cuts are moved into processing within hours of filleting and kept cold, then treated with enzymes that release the oil from the fish — a process called enzymatic hydrolysis. The oil separates and is filtered. It is not pressed, bleached, distilled, or re-esterified.

Why do most fish oil products concentrate at all?

Because EPA and DHA are the two omega-3s with the deepest research base, and a higher milligram figure is easier to advertise and easier to compare across a shelf. Concentrating is a rational response to how the category is shopped. It is a manufacturing decision about what to put on the label, not a finding about what the body uses best.

Sources 

• Utilizing the omega-3 index to assess the relative bioimpact of a whole salmon oil compared to a concentrated omega-3 oil. Functional Foods in Health and Disease, 2026. Registered as ClinicalTrials.gov NCT06802068 (sponsor: Hofseth Biocare ASA) — backs the 14-week trial design, the 84 participants, the 5.25% baseline, the 12% versus 7% Omega-3 Index increases, the 4.3-fold per-100 mg figure, and the inflammatory marker results. Industry-funded; disclosed in the body copy. 

• Harris WS, von Schacky C. The Omega-3 Index: a new risk factor for death from coronary heart disease? Preventive Medicine. 2004;39(1):212-220. DOI: 10.1016/j.ypmed.2004.02.030 — backs the 8% desirable threshold referenced in the trial section. 

• Minton ST, Almada AL, Evans JL, Laidlaw M, Opheim J. Comparative membrane incorporation of omega-3 fish oil triglyceride preparations differing by degree of re-esterification. PLOS ONE. DOI: 10.1371/journal.pone.0265462 — backs the finding that re-esterification is often incomplete, at roughly 55 to 60%.