Fish oil lowers plasma lipid concentrations and increases the susceptibility of low-density lipoprotein to oxidative modification in healthy men.

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Po-Jung Tsai and Shao-Chun Lu

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This study was designed to investigate the effects of fish oil on plasma lipid and lipoprotein concentrations and on the susceptibility of low density lipoprotein (LDL) to oxidation in normolipidemic young men. Two groups of eight men were assigned to a low cholesterol (50 mg/4187 kJ) or a high cholesterol (250 mg/4187 kJ) diet. Both groups consumed n-6 polyunsaturated fatty acid (PUFA)-rich soybean oil diets for 3 weeks, followed by n-3 PUFA-rich fish oil diets for 3 weeks. The fish oil diet significantly reduced the plasma concentrations of total cholesterol, total triglyceride, very low density lipoprotein (VLDL)-cholesterol, and VLDL-triglyceride (p < 0.05) compared with the soybean oil diet, irrespective of dietary cholesterol content. The fish oil diet increased incorporation of eicosapentachoic acid into LDL particles, shortened the lag time for conjugated diene formation in LDLs, and increased the production of thiobarbituric acid-reactive substances after exposure of LDL to 10 mumol/L Cu2+. Gel chromatographic analysis indicated that LDL particles obtained at the end of the fish oil diet were smaller than those obtained after the soybean oil diet. There was no significant difference between the low and high cholesterol groups in the parameters mentioned above during the 6-week treatment period. Our results suggest that fish oil lowers plasma lipid levels significantly but results in a form of LDL that is more susceptible to oxidation in vitro.