Effect of dietary monounsaturated and polyunsaturated fatty acids on the susceptibility of plasma low density lipoproteins to oxidative modification.

Oxidized low density lipoproteins (LDLs) are thought to play an important role in atherogenesis. Nutritional and biochemical studies suggest that diet can modulate the susceptibility of plasma LDL to undergo oxidative degradation by affecting the concentration of polyunsaturated fatty acids and antioxidants in the lipoprotein particle. In the present study 11 healthy male volunteers underwent two diet phases. In one phase the diet was enriched in oleic acid (mono), while in the other it was high in linoleic acid (poly). Both diets lowered plasma total and LDL cholesterol contents. The sensitivity of plasma LDL to oxidation was estimated by challenging these lipoproteins with 2,2'-azobis(2-amidinopropane)dihydrochloride, a free-radical initiator. Although neither diet affected the antioxidant content of plasma LDL, the resistance to lipid peroxidation, measured after the consumption of antioxidants present in the lipoprotein, was higher during the mono phase. Indeed, the peroxidation rate of plasma LDL was inversely correlated with the oleic acid to linoleic acid ratio in the LDL particle. These results support the thesis that diets rich in monounsaturated fatty acids increase the resistance of plasma LDL to oxidative modification, independent of their content of antioxidants. This effect could lower the atherogenicity of these lipoproteins.