CLINICAL STUDY Oleic acid from cooking oils is associated with lower insulin resistance in the general population (Pizarra study) F Soriguer, I Esteva, G Rojo-Martı ´nez, M S Ruiz de Adana, M C Dobarganes 1 , J M Garcı ´a-Almeida, F Tinahones, M Beltra ´n, S Gonza ´lez-Romero, G Olveira and J M Go ´mez-Zumaquero Servicio de Endocrinologı ´a y Nutricio ´n, Hospital Civil (Hospital Universitario Carlos Haya), Malaga, Spain and 1 Instituto de la Grasa (CSIC), Sevilla, Spain (Correspondence should be addressed to Federico Soriguer, Servicio de Endocrinologı ´a y Nutricio ´n, Hospital Civil, Plaza del Hospital Civil, 29009 Malaga, Spain; Email: federico.soriguer.ssps@juntadeandalucia.es) Abstract Aim: To evaluate the relation between type of dietary fatty acid and degree of insulin resistance. Design: A cross-sectional study. Methods: Anthropometrical data were measured in 538 subjects, aged 18– 65 years, selected ran- domly from the municipal census of Pizarra (Spain). An oral glucose tolerance test (OGTT) was given to all subjects and measurements were made of glycemia, insulinemia and the proportion of fatty acids in plasma phospholipids. Insulin resistance (IR) was estimated by homeostasis model assessment. Samples of cooking oil being used were obtained from the kitchens. The strength of association between variables was measured by calculating the odds ratio (OR) from logistic models, and the relationships were measured by linear correlation coefficients. Results: Insulin resistance was significantly less in people who used olive oil compared with those who used sunflower oil or a mixture. Statistical significance remained in the group of people with normal OGTTafter adjusting for obesity. In the whole sample, IR correlated negatively with the concentration of oleic acid (r ¼ 2 0.11; P ¼ 0.02) and positively with that of linoleic acid (r ¼ 0.10; P ¼ 0.02) from the cooking oil. In subjects with normal OGTT, IR correlated negatively with oleic acid from cooking oil (r ¼ 2 0.17; P ¼ 0.004) and from plasma phospholipids (r ¼ 2 0.11; P ¼ 0.01) and positively with the concentration of linoleic acid in cooking oil (r ¼ 0.18; P ¼ 0.004) and plasma phospholipids (r ¼ 0.12; P ¼ 0.005). The risk (OR) of having raised IR was significantly lower in people who con- sumed olive oil, either alone (OR ¼ 0.50) or mixed (OR ¼ 0.52) compared with those who consumed only sunflower oil. Conclusion: There is an association between the intake of oleic acid, the composition of oleic acid in plasma phospholipids and peripheral insulin action. European Journal of Endocrinology 150 33–39 Introduction Insulin resistance, glucose intolerance and hyperinsu- linemia are the main components of the metabolic syndrome (1) and probably precede the onset of type 2 diabetes mellitus (2). The prevalence of obesity, type 2 diabetes mellitus and other risk factors associated with the metabolic syndrome have increased markedly in the developed world (3). The roles of genetics and lifestyle in this increase are under debate (4). Although Himsworth showed that macronutrients in the diet can influence glucose tolerance in healthy subjects (5), studies of the role of diet in the risk of diabetes have been inconsistent. Some authors have found no associ- ation (6, 7) whereas others have found some degree of association with a particular nutrient (8, 9). Most population studies have focused on evaluating the relationship between diet and risk of type 2 diabetes mellitus. Overall, they indicate that intake of fats, especially saturated fats, has an adverse effect on the risk of diabetes, whilst intake of fibre is beneficial (10). There is general agreement about increased insu- lin resistance with saturated fatty acids (11) and reduced insulin resistance with n-3 fatty acids (12), although the effect of n-6 fatty acids on insulin resist- ance is controversial (13). The association between dietary intake of oleic acid and insulin resistance is less well understood. A relationship has been found between insulin resistance and levels of some monoun- saturated fatty acids (MUFA), such as palmitoleic acid (14), but studies of oleic acid have reported contradic- tory results. Some studies have shown a reduction in insulin resistance with diets rich in oleic acid (15), whereas others have either found no relationship (16) or have even shown an inverse association between oleic acid and insulin sensitivity (17). European Journal of Endocrinology (2004) 150 33–39 ISSN 0804-4643 q 2004 Society of the European Journal of Endocrinology Online version via http://www.eje.org