Dietary habits affect the susceptibility of low-density lipoprotein to oxidation

Objective: To study, if there are differences in the fatty acid composition of low-density lipoprotein (LDL) in people eating three different long-standing habitual diets: vegetarian, high fish intake, or high saturated fat (milk fat) diet as a control group, and to study if these differences influence the oxidation susceptibility of LDL. Design: Cross-sectional study using blood samples and a validated dietary frequency questionnaire with illustrations. Setting: Helsinki University Central Hospital, Finland. Subjects: The effect of three different types of long-standing diets of different fatty acid content (a strict vegetarian diet, n =11; a high fish intake diet, n= 9; and a high saturated fat (milk fat) diet, controls, n =7) on the serum and LDL fatty acid content, and on the susceptibility of LDL to oxidation in vitro, was studied in healthy normocholesterolemic volunteers who had been on these diets for years. Oxidation of LDL was carried out by using CuSO4 as a pro-oxidant. Results: There were no statistically significant differences in the serum lipids or lipoproteins, though the vegetarian group exhibited lowest mean values of total, high-density lipoprotein (HDL) and LDL cholesterol levels. Both the serum and LDL eicosapentaenoic, docosapentaenoic and docosahexaenoic acid proportions were highest in the fish and lowest in the vegetarian groups. Linoleic acid was highest among the vegetarians. In the fish group, the vitamin A concentration in serum was higher than in vegetarians and controls and beta-carotene lower than in controls, but in alpha-tocopherol, or lycopene concentrations there were no statistically significant differences. The lag phase of LDL oxidation was shortest (116 min) in the fish group and longest (165 min) in the vegetarian group, and the control group was between them (129 min). The mean oxidation percentage after 2.5 h of copper-induced oxidation was highest (44%) in the fish group and lowest (22%) in the vegetarian group and intermediate (31%) in the control group. Conclusion: Long-term dietary habits predict the fatty acid composition of serum and LDL, and influence the susceptibility of LDL to oxidation. In the fish group with the highest content of omega-3 fatty acids in LDL, the oxidation susceptibility of LDL was highest. In the vegetarian group with less omega-3 fatty acids in LDL, the LDL was more resistant to oxidation. Sponsorship: Helsinki University Central Hospital.