Dietary habits affect the susceptibility of low-density lipoprotein to oxidation R Korpela 1,2* , L Seppo 1,2 , J Laakso 1 , J Lilja 3 , K Karjala 1 , T La ¨hteenma ¨ki 1 , E Solatunturi 1 , H Vapaatalo 1 and MJ Tikkanen 3 1 Institute of Biomedicine, Department of Pharmacology and Toxicology, PO Box 8, FIN-00014 University of Helsinki; 2 Foundation for Nutrition Research, PO Box 30, FIN-00039 Valio, Helsinki; and 3 Helsinki University Central Hospital, Department of Medicine, Haartmaninkatu 4, FIN-00290 Helsinki, Finland 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 CuSO 4 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 b-carotene lower than in controls, but in a-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. Descriptors: oxidation; LDL; cholesterol; diet; fish;vegetarian; polyunsaturated fatty acids; saturated fatty acids; antioxidants Introduction Dietary fatty acids affect low-density lipoprotein (LDL) oxidation by changing its fatty acid composition (Berry et al, 1991; Reaven et al, 1993; Reaven, 1996). Of the fatty acids, polyunsaturated fatty acids are the most susceptible to oxidation (Bonanome et al, 1992; Reaven et al, 1993), and a diet enriched with linoleic acid increases LDL oxidation in both human (Berry et al, 1991; Reaven et al, 1991; Bonanome et al, 1992; Abbey et al, 1993; Corboy et al, 1993; Reaven et al, 1993; Reaven et al, 1994; Wink- lerhofer-Roob et al, 1995; Louheranta et al, 1996) and animal experiments (Thomas & Rudel, 1996). Lag time before the onset of the propagation phase of oxidation in vitro has been shown to be shortened (Abbey et al, 1993) or not altered (Reaven et al, 1991) by a linoleic acid rich diet. Fish diet is rich in polyunsaturated long-chain omega-3 fatty acids, especially eicosapentaenoic acid (EPA) and docosahexanoic acid (DHA), which are susceptible to oxidation (Gonzales et al, 1992) and supplementation of the diet with omega-3 fatty acids increases LDL oxidation in healthy subjects (Oostenburg et al, 1994; Suzukawa et al, 1995; Palozza et al, 1996), in hypertriglyceridemic patients (Hau et al, 1996), and in patients with non- insulin-dependent diabetes mellitus (McGrath et al, 1996). On the other hand, Bonanome et al (1996) in humans and Thomas & Rudel (1996) in non-human pri- mates did not find any change due to supplementation with *Correspondence: Riitta Korpela, Institute of Biomedicine, Department of Pharmacology and Toxicology PO Box 8, FIN-00014 University of Helsinki, Finland. Email: riitta.korpela@valio.fi Contributors: R Korpela: responsible for the dietary part, manuscript; L Seppo: subject recruiting, recording and calculating the living habits, dietary and nutrient intake; J Laakso: determination of LDL fatty acids; J Lilja: member of the study group; K Karjala: member of the study group (effects on vascular response); T La ¨hteenma ¨ki: member of the study group (effects on proliferative effects); E Solatunturi: member of the study group (effects on platelet aggregation); H Vapaatalo: responsible for all the measurements, study initiator, study plan; MJ Tikkanen: LDL oxidation. Received 22 December 1998; revised 30 March 1999; accepted 7 May 1999 European Journal of Clinical Nutrition (1999) 52, 802–807 ß 1999 Stockton Press. All rights reserved 0954–3007/99 $15.00 http://www.stockton-press.co.uk/ejcn