Absorption and transport of fat in mammals with emphasis on n-3 polyunsaturated fatty acids.

The current state of knowledge concerning the absorption and transport of dietary fat with emphasis on long-chain polyunsaturated n-3 fatty acids in mammals is reviewed. It is apparent that long-chain polyunsaturated n-3 fatty acids, either as free acids or as part of triglycerides, are readily absorbed in the gut and transported by the circulatory system. Indeed, it would appear that long-chain polyunsaturated n-3 fatty acids are digested, absorbed and transported similarly to other long-chain fatty acids with only minor variations, although there is much that is still not understood about these processes. The main unresolved issues in the area of the absorption and transport of long-chain polyunsaturated n-3 fatty acids appear to be: 1) If they, when located in the 2-position of triglycerides, have unique metabolic pathways; and 2) whether the unnatural forms, i.e., methyl or ethyl ester derivatives, are suitable vehicles for administration as dietary supplements. The effect in man of dietary, long-chain polyunsaturated n-3 fatty acids on blood serum lipid and lipoprotein levels, particularly the low density lipoproteins, remains controversial, except for the well-documented reduction in serum triglyceride levels. Also, there is uncertainty regarding their distribution and metabolism in tissues. Finally, if the consumption of long-chain polyunsaturated n-3 fatty acids has beneficial health consequences, what is the appropriate therapeutic dose? In view of these important, unresolved issues and uncertainties, it would seem prudent to direct additional research toward a better understanding of the overall process by which fat is digested, absorbed and transported.