Marine long chain polyunsaturated fatty acids are known to be beneficial to the health, particularly with regard to their preventative role in cardiovascular disease. Many studies have measured the incorporation of eicosapentanoic acid (EPA, C20:5, n-3) and docosahexanoic acid (DHA, C22:6 (n-6) into the membranes of plasma phospholipids and plasma triacylglycerols. High levels of long chain PUFA in these membranes are thought to reduce thrombotic and atherogenic processes and are thus of interest nutritionally. Research1 suggests that the location of DHA or EPA fatty acid bonded to the glycerol (sn-1, sn-2 or sn-3) on the dietary fish oils triacylglycerols may affect the subsequent distribution of the fatty acids into triacylglycerols, cholesterol esters (CE) and phospholipids of low density lipoproteins (LDL), very low density lipoproteins (VLDL) and high density lipoproteins (HDL).
For example, researchers fed nine healthy volunteers 2 grams of EPA and 1.3 grams of DHA in fish oil capsules for up to 30 days. The fish oil capsules used had triacylglycerols where the DHA was predominately situated in the sn-2 position. Supplementation of the fish oil capsules caused a steady increase in the levels of n-3 fatty acids in lipoproteins to a maximum of around 4% of total fatty acids by day 30. DHA appeared to be preferentially incorporated into LDL and VLDL triacylglycerols and this reached a maximum at around day 15. The ratio of EPA to DHA was 0.7 in the LDL/VLDL triacylglycerol fraction, but 1.5 in fish oil triacylglycerols. About one-fifth as much DHA and EPA were incorporated into HDL triacylglycerols but maximum levels were again reached at around day 15. Short-term increases (<24 hours) in EPA and DHA resulted from rapid incorporation to plasma triacylglycerols.
As levels of n-3 fatty acids increased, levels of oleic, palmitic and linoleic acids fell. Very little of the DHA was incorporated into the CE of lipoproteins. However, CE did contain high amounts of EPA which reached its maximum at around day 15. The maximum value of EPA was two times higher in the LDL and VLDL fraction compared to the HDL fraction. The total EPA and DHA concentrations incorporated into triacylglycerols, cholesterol esters and phospholipids were 309 and 192 µmol/L, respectively. The ratio of these values (2:1.3) shows that the EPA to DHA ratios were the same as were present in the fish oil supplements. However, while both fatty acids were mainly incorporated into phospholipids of LDL, VLDL and HDL (55% total EPA versus 59% total DHA), EPA was preferentially incorporated into CE (28% total EPA versus <6% total DHA), and DHA is preferentially incorporated into triacylglycerols (35% total DHA versus 17% total EPA).
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