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Fish Oil Absorption: The bioavailability of the natural triglycerides vs. synthetic ethyl esters.

Much emphasis has been placed on fish oil quality and purity but another critical factor to be considered for fish oils is bioavailability (the body's ability to utilize a substance). Numerous studies have addressed this issue and have presented evidence that fish oil in its natural triglyceride form is substantially better absorbed than the synthetic ethyl ester form. The ethyl ester form of EPA and DHA is synthesized through a reaction between ethanol and fatty acids during a process called molecular distillation. The triglyceride form is naturally occurring and is made up of three fatty acids bound to a glycerol backbone. The omega-3 fatty acids EPA and DHA present in PRN are in the natural triglyceride form.

In a study comparing the absorption after a single dose of different fish oil forms, the natural triglyceride form was 300% better absorbed than the synthetic ethyl ester form. (1) Another study looking at the bioavailability of EPA and DHA found the ethyl ester form to be 40% and 48% less absorbed for EPA and DHA respectively as compared to EPA and DHA in the natural triglyceride form. (2)

One of the apparent reasons for the poor bioavailability of the ethyl ester form is due to its greater resistance to digestive enzymes. During the digestive process, pancreatic lipase enzymes hydrolyse (cleave) the oils to liberate the fatty acids. This stage of digestion prepares the fatty acids for subsequent absorption. The ethyl ester form has been demonstrated to be 10-50 times more resistant to this enzymatic process than the natural triglyceride form. (3) Since our bodies can only use nutrients that get absorbed, consuming omega-3 fatty acids in their natural triglyceride form offers substantially better absorption over the ethyl ester form.


(1) Lawson LD, Hughes BG., 1988. Absorption of eicosapentaenoic acid and docosahexaenoic acid from fish oil triacylycerols or fish oil ethyl esters co-ingested with a high-fat meal. Biochem Biophys Res Commun. Oct 31; 156(2):960-3

(2) Beckermann B., Beneke M. Steitz I., 1990. Comparative bioavailability of eicosapentaenoic acid and docasahexaenoic acid from triglycerides, free fatty acids and ethyl esters in volunteers. Arzneimittelforschung. June; 40(6):700-4

(3) Yang LY, Kuksis A, Myher JJ., 1990. Lipolysis of menhaden oil triacylglyerols and the corresponding fatty acid alkyl esters by pancreatic lipase in vitro: a reexamination. J Lipid Res. 1990 Jan; 31(1):137-47