Incidence of obesity is lower in persons who consume olive oil

Abstract

We undertook a population-based cohort study in Pizarra (Spain). Anthropometric and nutritional variables were recorded for 613 persons. The type of fat used was determined by measurement of the fatty acids contained in cooking oil. Serum fatty acid was used as a biological marker of the type of fat consumed. Obesity incidence in persons who were not obese at baseline was greater in those who consumed sunflower oil (Group 1: 41.5 (95% CI, 25.4–67.8) cases per 1000 person-years) than in those who consumed olive oil or a mixture of oils (Group 2: 17.3 (95% CI, 11.6–25.8) cases per 1000 person-years). The risk of developing obesity over 6 years, adjusted for age, sex, physical activity, smoking, instruction level, energy intake and baseline BMI, was 2.3 (95% CI, 1.06–5.02) in group 1 compared with that in group 2. The increase in the prevalence of obesity in the free-living population is associated with the type of fatty acids in the diet.

Main

Two of the most important factors contributing to the increased prevalence of obesity in the world are the reduction in physical exercise and an increased intake of energy. The importance of fats is more controversial. Studies examining the type of dietary fat have either found a weak positive association with intake of animal fats and a negative association with intake of vegetable fats (Colditz et al., 1990) or else no association between the type of dietary fat and prevalence of obesity (González et al., 2004). The role of mono-unsaturated fatty acid (MUFA) in the control of body weight has been poorly studied. We tested the hypothesis that the incidence of obesity in the population is associated with the type of fatty acids in the diet.

The study was undertaken in Pizarra (southern Spain). Details of the design and sample have been reported previously (Soriguer et al., 2003, 2008). A total of 613 individuals, aged 18–65 years, were randomly selected for a dietary survey from the initial sample of 1226 individuals, who were also randomly selected from the population census (Figure 1). Written consent was obtained.

Figure 1
figure1

Pizarra study sampling.

Measurements of weight, height and waist circumference were determined, and body mass index (BMI) was calculated.

The fatty acid composition of serum phospholipids was measured by gas chromatography in fasting venous blood samples, as reported (Soriguer et al., 2003).

A prospective, quantitative, 7-day food questionnaire was administered to all participants and a sample was taken of the cooking oil being used for analyzing fatty acids by gas chromatography (Soriguer et al., 2003). Oils having concentrations of linoleic acid higher than 50% were classified as sunflower oil, otherwise as olive oil or a mixture. The concordance between the type of oil declared in the questionnaire and that detected by chromatography was above 85%. Obesity was set at a BMI of 30 kg/m2 or above. The cohort was reevaluated 6 years later (6.0±1.3 years). The outcome variable was obesity.

Adjusted contrast hypothesis testing with continuous variables was carried out using ANOVA, and the χ2-test was used for qualitative variables. Relative risk was calculated by logistic regression analysis.

Table 1 shows the characteristics of the individuals at risk (those with a BMI <30 kg/m2 in the baseline study) according to the type of oil consumed. No significant differences were found in the age (39.0±13.3 years) or sex ratio (men=37.1%). Baseline weight, BMI and waist circumference were higher in persons who consumed sunflower oil, although the differences were not significant when adjusted for age and sex. There were no differences with regard to physical activity, smoking or education level.

Table 1 Characteristics of the study population (only those with BMI<30 in the baseline study) according to the type of oil consumed

The fatty acids from serum phospholipids followed the expected pattern, with persons who consumed olive oil having a greater proportion of MUFA, a lower proportion of polyunsaturated fatty acids and a higher oleic acid:stearic acid ratio. Energy intake and macronutrient intake were similar in both groups, in baseline and follow-up studies, but as expected, the proportion of dietary fatty acids varies according to the type of oil consumed.

The incidence of obesity was significantly higher in those who consumed sunflower oil than in those who consumed olive oil or a mixture (Table 2). Persons who consumed olive oil had a lower risk of being obese at follow-up, adjusted for age, sex, physical activity, smoking, instruction level, energy intake and BMI in the baseline study (similar results are obtained in the function of basal weight).

Table 2 Risk of obesity at follow-up

The increase in BMI over the study period in persons who were not obese at baseline was significantly higher in those with a lower phospholipid oleic acid : stearic acid ratio: 8.3±15.03% in the lowest tertile, 5.6±9.1% in the highest tertile, P=0.009 adjusted for age and sex.

The increased consumption of saturated fats has generally been considered to favor weight gain, whereas fats rich in n-6 or n-3 fatty acids may be associated with a reduced weight gain (González et al., 2004). Studies comparing MUFA with carbohydrate-rich diets show that weight loss is determined more by energy restriction than by diet composition (Golay et al., 1996). The SUN prospective cohort study found no significant association between consumption of olive oil and weight gain, possibly because of a short follow-up time (Bes-Rastrollo et al., 2006). Schröder et al. (2004), in a cross-sectional survey, found that the traditional Mediterranean dietary pattern was inversely associated with BMI and obesity. Trichopoulou et al. (2002), in another cross-sectional study, found a weak, inconclusive negative association between MUFA and BMI.

The MUFA could act selectively on satiety, increasing the rate of postprandial oxidization, increasing adipocyte lipolytic activity or having a thermogenic effect. MUFA could also affect body weight by modulating levels of cytokines. Most industrialized countries have experienced a continuous increase in the amount of linoleic acid in the diet. Ailhaud and Guesnet (2004) have proposed that an increase in the consumption of n-6 polyunsaturated fatty acids may favor the continuous development of adipose tissue during pregnancy and lactation. This early stimulation of adipocytes and preadipocytes could be the onset of adult obesity, especially if diets rich in n-6 polyunsaturated fatty acids continue throughout life.

Persons who consume more olive oil may have a different dietary behavior and may consume more dietary calories (Serra-Majem et al., 2003). This observation would strengthen the results of our study as, if true, the higher intake of calories would not favor the lower weight gain seen in persons who habitually consumed olive oil. In our study, the persons who consumed mainly sunflower oil had a similar intake of energy and macronutrients to those who consumed olive oil. The association between the increase in BMI and the oleic:stearic acid ratio in the serum phospholipids followed the same trend as the association between weight, BMI and waist circumference and the type of oil collected, suggesting that the association is not due to a confounding environmental or cultural variable, but rather to the biological effect of MUFA measured by their uptake into serum phospholipids.

Conflict of interest

The authors declare no conflict of interest.

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Acknowledgements

We are grateful to Isabel Cardona for her inestimable technical help and to Ian Johnstone for his help with the English language version of the paper. This study was undertaken with finance from the Fondo de Investigación Sanitaria (PI041883, PI051307), Junta de Andalucía (0124/2005, P06-CTS-01684) and the Fundación Centro de Excelencia en investigación sobre Aceite de oliva y Salud (CEAS).

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Correspondence to G Rojo-Martínez.

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Contributors: FS, IE and GR-M contributed to the study design, GR-M, MCA, JMGA, MSRdA, FL, EG-E, SM and GO-F contributed in the data collection, FS and GR-M contributed in the data analysis, all authors contributed in writing the paper.

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Soriguer, F., Almaraz, M., Ruiz-de-Adana, M. et al. Incidence of obesity is lower in persons who consume olive oil. Eur J Clin Nutr 63, 1371–1374 (2009). https://doi.org/10.1038/ejcn.2009.65

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Keywords

  • olive oil
  • obesity incidence
  • population-based cohort study

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