AbstractBackgroundAlthough the fatty acid fractions provide similar metabolizable energy, the type of dietary fat consumed could be relevant to the development of obesity.ObjectiveTo investigate the relationship between body mass index (BMI), obesity and the consumption of different types of fat and olive oil in a Mediterranean country with high prevalence of obesity, and high intake of monounsaturated fatty acids (MUFA) and olive oil.SubjectsThe study was carried out in Spain among 23 289 women and 14 374 men, aged 29–69 years, who were participants of a large European prospective cohort.MethodsInformation on usual food intake was collected by interviewers by means of a dietary history questionnaire. The association between obesity (BMI ≥ 30 kg m²), dietary fat, other dietary patterns and other non-dietary factors were tested using multilinear regression analysis. The ratio of reported energy intake to energy requirement was used as an estimation of dietary underreporting.ResultsThe association between fatty acid fractions intake (saturated fatty acids (SFA) in women, and MUFA and polyunsaturated fatty acids (PUFA) in both sexes) and BMI was very weak, accounting for less than 1% of variance. All dietary and non-dietary variables accounted for 21% of variance in the measurement of BMI in women and only 6.7% of variance in men. Estimated underreporting of energy intake was 17.5% in obese women and 5.5% in obese men.ConclusionsThe association between consumption of specific types of dietary fat, olive oil and obesity in Spain is not very important. However, because of the cross-sectional design and some level of underreporting of energy intake observed in overweight subjects and overreporting in underweight subjects, systematic bias cannot be completely discarded.