Digestion, absorption and deposition of n-3 polyunsaturated fatty acids in tissues: is the chemical form of supply relevant?

The n-3 polyunsaturated fatty acids (n-3 PUFAs) are relevant nutrients for human health, but cannot be synthesized autonomously, with α-linolenic being a precursor of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids. EPA and DHA occur naturally in seafood, but n-3 PUFAs supplements vary in formulation and composition. Fish oil triglycerides (TGs) are the most common form, but phospholipids (PLs) and ethyl esters are also used. The bioavailability of DHA at the intestinal level depends on the position of DHA in the molecule, with the sn-2 form being more bioavailable than the sn-1 and sn-3 forms. Formulations with high amounts of DHA in PLs form, such as krill oil supplements, have a higher bioavailability than common TG-based fish oil. Ethyl ester formulations, although more stable to oxidative processes, depend on pancreatic enzyme activity and lipid intake at each meal to ensure absorption. DHA deposits in tissues such as heart, liver and brain correlate with bioavailability, with PLs and TGs of DHA being found in the highest amounts in these tissues, making the bioavailability of n-3 PUFAs supplements a challenge for the pharmaceutical industry. Formulations with high amounts of DHA in the form of PLs offer higher bioavailability but are more expensive than other formulations.