Polyunsaturated fatty acids of tuna orbital adipose tissue constitute 40.06 % of the total fatty acids, and DHA is the most abundant one which constitutes 30.57 % of the total fatty acids.
Marine fish are the main source for EPA- and DHA. The amount of LC n-3 PUFAs varies considerably between fish species. Oily fish generally contains higher LC n-3 PUFA levels compared to lean fish. The habitat of the fish also plays an important role. LC n-3 PUFAs are primarily found in cold-water fish like cod, herring, mackerel, salmon, anchovy, menhaden, and sardine. An exception is tuna (e.g., Albacore), which as a warm-water fish also contains comparatively high LC n-3 PUFA contents.
FOs derived from these fishes are highly susceptible to oxidation and must be refined to remove contaminants, and undesirable substances (such as non-esterified fatty acids, oxidation products, and environmental toxins) to produce edible oils for the use as drug, dietary supplement or additive to foods. This process typically includes steps such as degumming, neutralization, bleaching, and deodorization. Refined unconcentrated FO make up the majority of all n-3 oils for dietary supplements [8]. These oils contain approximately 18 % EPA and 12 % DHA relative to the total amount of FA. EPA and DHA are mainly bound to TAGs and, to a lesser extent, as NEFA. With around 30 % EPA and DHA content, each TAG molecule typically contains one long-chain (LC) n-3 PUFA. In natural “unmodified” TAGs (uTAGs), about 50 % of EPA or DHA are bound at the 2-position (sn-2), while two other short-chain or mid-chain FA are bound in the 1- and 3-positions (sn-1/3) [9,10]. A smaller proportion of EPA and DHA in uTAG is esterified in positions sn-1 and sn-3.
Thus, this review aims to describe the influence of fish oil processing on the omega-3 bioavailability in humans.
Currently, omega-3 is more bioavailable when ingested as free fatty acid, followed by triglyceride, and lastly as ethyl ester.
Due to their high susceptibility to oxidation and preliminary findings, administering omega-3 in the form of triglyceride may be the most suitable to maximize bioavailability.
Fish oil is routinely concentrated into unmodified triglycerides, or trans-esterified into an ethyl ester form. Re-esterification of the ethyl ester form yields re-esterified triglycerides (rTG), which are reportedly more bioavailable than ethyl ester forms. However, the fidelity of the re-esterification process may yield variable triglyceride forms, with only 55–60% being rTG.
The apparent bioavailability (as defined by the authors of these studies) seems to be lowest for the EE form and highest for the FFA form, whilst no conclusion can be made for TAG versus PL from human data.
The major limitations with the studies to date include: (between studies) loose definition of the term "bioavailability", lack of standardisation of analytical methodology, and differences in which blood compartment was analysed; (within a study) failure to provide equal amounts the n-3 LC-PUFA of the different forms being compared, failure to provide the dose of n-3 LC-PUFA on a body weight basis, failure to measure fatty acid excretion, failure to control the total fat intake, and failure to adequately power the studies from a statistical point of view.
Acute bioavailability differences often do not persist in chronic supplementation.
長期補充的話，（不同型態的魚油）生物利用率不一定有明顯差別
Bioavailability for isolated chemically forms followed the order: NEFA > PL > rTAG > unmodified TAG > ethyl esters (EE).
Significant differences observed in acute bioavailability studies (e.g., faster absorption) often did not translate into long-term impacts in chronic supplementation studies.
These data suggest that the percentage of rTG in rTG fish oil preparations may evolve as a new chemoprofile/quality control marker that can influence its lipidomic pharmacodynamics. Additional investigations to assess the physiologic/vascular and metabolic/inflammasome responses to concentrated fish oil preparations differing in the percentage of rTG are warranted.
● One group received a >95% rTG (Ultimate Omega®), as 1,000 mg capsules containing 325 mg eicosapentaenoic acid (EPA) and 225 mg docosahexaenoic acid (DHA) = 325 mg EPA + 225 mg DHA
● the other received a <70% rTG (MEG-3) as 1,000 mg capsules containing 300 mg EPA and 200 mg DHA = 300 mg EPA + 200 mg DHA
Commonly reported side effects of omega-3 supplements are usually mild. These include unpleasant taste, bad breath, heartburn, nausea, gastrointestinal discomfort, diarrhea, headache, and odoriferous sweat [161,190].
The FDA-approved fatty acid prescriptions (icosapent ethyl, omega-3-acid ethyl esters, omega-3-carboxylic acids, and omega-3-acid ethyl esters A) are generally safe with benign effects such as fishy taste, eructation, dyspepsia, diarrhea, gas, nausea, and arthralgia.
Commonly reported side effects of omega-3 supplements are usually mild. These include unpleasant taste, bad breath, heartburn, nausea, gastrointestinal discomfort, diarrhea, headache, and odoriferous sweat [161,190].
The U.S. Food and Drug Administration recommends consuming no more than 5 g/day of EPA and DHA combined from dietary supplements. Any side effects from taking omega-3 supplements are usually mild. They include an unpleasant taste in the mouth, bad breath, heartburn, nausea, stomach discomfort, diarrhea, headache, and smelly sweat.
The FDA-approved fatty acid prescriptions (icosapent ethyl, omega-3-acid ethyl esters, omega-3-carboxylic acids, and omega-3-acid ethyl esters A) are generally safe with benign effects such as fishy taste, eructation, dyspepsia, diarrhea, gas, nausea, and arthralgia.[4][64][65] Researchers noted adverse reactions in clinical trials for each FDA-approved omega-3 fatty acid product.[4][3][6]
