The results of a clinical trial from Norway add more evidence in support of the hypothesis that people absorb the omega-3s in whole fish better than the omega-3s in some fish oils.
We reported on this topic back in 2005 (see "Natural Omega-3s Seen Superior”) when the evidence available then favored whole fish—in which omega-3s occur in the form of triglycerides—and the majority of fish oils (including all of ours) whose omega-3s occur in the form of triglycerides.
About 10 percent of refined fish oils (which dominate the market) contain the ethyl ester form of omega-3s. The omega-3s in virtually all unrefined fish oils exist in the triglyceride form.
Half of the four extant studies comparing the two forms found that triglyceride-form omega-3s were absorbed at significantly higher rates. The other two studies found the two forms were absorbed at equal rates.
(Once they are absorbed, the human body converts omega-3s back and forth between the triglyceride and ethyl ester forms routinely, as needed.)
Given the mixed results of the four extant head-to-head tests, we cannot be sure that the form in which dietary omega-3s occur—triglyceride and ethyl ester—is the key factor determining the percentage of omega-3s absorbed into our cells.
But a study from 2003 showed that omega-3s were absorbed better from salmon than from fish oil supplements (Visioli F et al 2003).
And new findings from Norway provide more evidence that people’s blood cells absorb omega-3s at higher rates from salmon than from fish oils.
Clinical trial confirms superior absorption of omega-3s from salmon
Researchers at the University of Tromsø, Norway set out to compare omega-3s from salmon versus omega-3s from cod liver oil capsules (Elvevoll EO et al 2006), with regard to three important impacts:
- Changes in blood levels of omega-3s
- Impact on blood fat profiles
- Impact on functional properties of blood cells (e.g., production of inflammatory chemicals)
They recruited 71 volunteers and divided them into five groups, each of which received omega-3s from a different source throughout the duration of the eight-week-long study:
- Cooked Salmon—14 ounces (400 gm) per week
- Smoked Salmon—14 ounces (400 gm) per week
- Cooked Cod—14 ounces (400 gm) per week
- Cod Liver Oil—3 teaspoons (0.5 oz or 15 milliliters) per day
- Control Group—no change to their usual diets
After eight weeks, the scientists re-tested the participants’ blood, with results strongly favoring fish as the source of omega-3s.
The key comparison was between the Cooked Salmon and Cod Liver Oil groups, whose regimens provided markedly different amounts of omega-3s:
- Cooked Salmon provided about 1.2 gm of omega-3s (EPA+DHA) per day.
- Cod Liver Oil provided 3 gm of omega-3s (EPA+DHA) per day
Thus, the Cooked Salmon group got less than half as much omega-3s per day compared with the Cod Liver Oil group.
Nonetheless, blood levels of omega-3s (EPA and DHA) increased significantly more in the Cooked Salmon group than they did in the Cod Liver Oil group.
The Cooked Salmon group enjoyed a 129 percent rise in EPA levels and a 45 percent rise in DHA levels versus increases of 106 percent and 25 percent, respectively, in the Cod Liver Oil group.
(The Smoked Salmon group experienced a smaller rise in omega-3 levels—about one-third less—compared with the Cooked Salmon group, while the Cooked Cod group showed only a very small rise in omega-3 levels.)
In addition, higher levels of omega-3 EPA and DHA yielded lower levels of certain inflammatory chemicals in the blood.
As the authors wrote, "In conclusion, fish consumption is more effective in increasing serum [blood] EPA and DHA [levels] than supplementing the diet with fish oil” (Elvevoll EO et al 2006).
The omega-3s in the salmon and the cod liver oil were both in the triglyceride form, which led the authors to speculate that the superior absorption of omega-3s from salmon might be linked to differences in the specific structure of its omega-3-containing triglycerides: "… it is suggested that the larger uptake from fish than CLO is due to differences in physiochemical structure of the lipids.”
This idea finds support from prior research in animals (Krokan HE et al 1993; Ikeda I et al 1995; Christensen MS et al 1995).
But they also proposed that eating whole fish confers certain digestive advantages, and their speculation on this point is worth quoting in full. We inserted clarifying comments and substitutions for technical terms between brackets [ ])
- "Conceivably, the greater uptake of [omega-3 fatty acids] from fish as compared with [Cod Liver Oil] might be attributed to the more diluted emulsion of [omega-3 fatty acids] when consumed in the form of fish fillets as compared with the intake of a… [large oral dose of omega-3s from]… [Cod Liver Oil].
- "This higher dilution [of omega-3s in fish] together with their incorporation within the food item may favor the processes that are involved in fat digestion and absorption… One may anticipate… [greater]… interaction between the food component and the intestinal wall together with a more favorable secretion of agents for the absorption of [omega-3] lipids.”
We cannot be certain what the Norwegians’ results say about absorption of omega-3s from our unrefined Salmon Oil, which come in the triglyceride form natural to fish and occur within the matrix of fatty acids and other lipids found in whole wild salmon.
But, taken together with the similar results from Italy, the Norwegians’ novel findings seem to support our own hypothesis, which is that a fish oil’s omega-3s will be absorbed more completely the more closely it matches the matrix of fats in whole fish.
We invite interested researchers to take up the challenge to test this hypothesis by testing our Sockeye Salmon Oil against a standard, distilled fish oil.
In the meantime, as advocates of whole food nutrition, we find it gratifying to see more evidence that omega-3s obtained by eating whole fish raise blood levels of omega-3s higher than the rises produced by greater amounts of omega-3s obtained from fish oil.
- Visioli F, Risé P, Barassi MC, Marangoni F, Galli C. Dietary intake of fish vs. formulations leads to higher plasma concentrations of n-3 fatty acids. Lipids. 2003 Apr;38(4):415-8.
- Elvevoll EO, Barstad H, Breimo ES, Brox J, Eilertsen KE, Lund T, Olsen JO, Osterud B. Enhanced incorporation of n-3 fatty acids from fish compared with fish oils. Lipids. 2006 Dec;41(12):1109-14.
- Christensen MS, Hoy CE, Becker CC, Redgrave TG. Intestinal absorption and lymphatic transport of eicosapentaenoic (EPA), docosahexaenoic (DHA), and decanoic acids: dependence on intramolecular triacylglycerol structure. Am J Clin Nutr. 1995 Jan;61(1):56-61.
- Ikeda I, Sasaki E, Yasunami H, Nomiyama S, Nakayama M, Sugano M, Imaizumi K, Yazawa K. Digestion and lymphatic transport of eicosapentaenoic and docosahexaenoic acids given in the form of triacylglycerol, free acid and ethyl ester in rats. Biochim Biophys Acta. 1995 Dec 7;1259(3):297-304.
- Krokan HE, Bjerve KS, Mork E. The enteral bioavailability of eicosapentaenoic acid and docosahexaenoic acid is as good from ethyl esters as from glyceryl esters in spite of lower hydrolytic rates by pancreatic lipase in vitro. Biochim Biophys Acta. 1993 May 20;1168(1):59-67.