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

Abstract

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.

Fish Intake, Independent of Apo(a) Size, Accounts for Lower Plasma Lipoprotein(a) Levels in Bantu Fishermen of Tanzania

“…The mechanisms linking high fish intake and lower Lp(a) levels in plasma are unclear, because it is unknown at this time whether n-3 PUFAs affect apo(a) synthesis or metabolism. It has been suggested 29 that an appreciable proportion of n-3 fatty acids may directly enter the portal vein system, producing profound effects on liver function, such as a marked reduction in serum triglycerides. It can be speculated that the n-3 fatty acids may lower the rate of apo(a) synthesis and/or secretion from the liver.…”

Brown fat thermogenesis in rats fed high-fat diets enriched with n-3 polyunsaturated fatty acids

“…13 On the other hand, the intestinal absorption does not differ between n-3 fatty acids and other fatty acids. 26 Accordingly, the higher gross food ef®ciency in the groups fed high-fat diets might result from the fact that the energy cost of lipid deposition from dietary lipids (5% of the energy potential of lipids) is considerably lower than that from dietary carbohydrate (25% of the energy potential of carbohydrate). 9,27 It must be kept in mind that DIT, in absolute terms, includes the the obligatory DIT (the cost of absorption, digestion and storage of nutrients) and the facultative DIT (the thermogenic effect of nutrients, mainly achieved by BAT).…”

Digestion and absorption of polyunsaturated fatty acids

“…In MaxEPA, a purified fish oil preparation, eicosapentaenoic acid occupies both the 2-and 1-, 3-positions and docosahexaenoic acid preferentially the 2-position (Chernenko et al, 1989 (Brindley, 1977; Thomson, 1978;Friedman and Nylund, 1980; Thomson and Dietschy, 1981;Tso and Simmonds, 1984;Bernard and Carlier, 1989;Thomson et al, 1989). Conversely, long-chain polyunsaturated fatty acid triglyceride digestion and absorption studies began only a few years ago (Nelson and Ackman, 1988) and sometimes gave conflicting results (McDonald et al, 1980;Chen et al, 1987b;Nilsson et al, 1987;Chernenko et al, 1989;Pavero et al, 1989). The assumption of most investigators was that polyunsaturated fatty acids are digested and absorbed through normal processes similar to those of mono-unsaturated long-chain fatty acids.…”