The participants were patients who referred for coronary angiography to the Shahid Rajaei Cardiovascular, Medical & Research Center, Tehran, Iran. Patients entered the study one month after undergoing angiography to ensure that their medical and pharmacological status was stable.
Eligible subjects were men and post-menopausal women less than 75 years of age who had at least one major cardiovascular risk factor, such as hypertension, diabetes mellitus, dyslipidemia, or acute cardiac event. The exclusion criteria were the regular use of anti-inflammatory medication, dietary antioxidants, or omega-3 supplements during the month prior to the study; any changes in the disease treatment plan, including type or dose of drugs or coronary artery bypass graft (CABG); and gastrointestinal complications such as diarrhea during the study. In addition, participants with low adherence to the intervention (who consumed less than 80% of the olive or canola oils delivered at baseline) were excluded from the study.
The present study was a randomized, controlled, open-label, parallel-arm clinical trial conducted in the spring and summer of 2019 in Tehran, Iran. The enrollment period ran from June 18, 2019 to September 15, 2019. At baseline, demographic and medical information was obtained through face-to-face interviews and reviews of medical files, respectively. Cardiovascular risk factors (hypertension, diabetes, and dyslipidemia) and past medical histories were determined from the patients' medical records. All participants received dietary advice on a heart-healthy diet at baseline. Daily consumption of at least five servings of fruits and vegetables, substituting lower-fat dairy products and meats for higher fats ones, and lower use of salt and simple sugars were among the dietary advice provided. Next, the participants were randomly assigned to one of the two groups in a 1:1 ratio following simple randomization procedures using computerized random numbers by one of the study researchers not involved in patient care. Participants were requested to consume a daily amount of 25 mL of refined olive oil (OO) (Etka, Roodbar, Iran) or canola oil (CO) (CanaPlus, British Columbia, Canada) raw with meals for 6 weeks. The fatty acid composition of OO and CO is shown in Table 1. Olive and canola oils were provided to patients in sufficient quantities. To ensure compliance with the intervention and proper oil consumption, participants were followed up weekly by telephone contact. If a participant consumed the recommended amount of oil (25 ml per day) less than 5 days a week, s/he was excluded from the study.
The procedures followed in this trial were in accordance with the 1964 Helsinki Declaration, and the study protocol was approved by the Ethics Committee of the National Nutrition & Food Technology Research Institute, Tehran, Iran (No. IR.SBMU.NNFTRI.REC.1398.074). Written informed consent was obtained from all participants prior to beginning the study. This clinical trial was registered at the Iranian Registry Center of Clinical Trials (IRCT) (registration number: 20160702028742N5).
Participant weight and height were measured at baseline and after 6 weeks of intervention by the study dietitian. Weight was measured without shoes, coats, or jackets using a digital scale. Height was measured without shoes using a wall-mounted stadiometer.
Venous blood samples were obtained from each patient after 12-h overnight fasting and collected into heparinized tubes at baseline and after 6 weeks of intervention. The blood samples were centrifuged (4000 rpm for 20 min), and the resulting plasma was stored at -80 °C. Plasma Lp-PLA2 mass and activity were analyzed by a commercially available ELISA kit (ZellBio GmbH, Ulm, Germany) and commercial colorimetric assay kit (Cayman Chemical, Ann Arbor, MI, USA), respectively. A commercially available ELISA kit (Biolegend, San Diego, CA, USA) was used to measure plasma IL-6 concentration. Plasma lipids and lipoproteins were analyzed using the colorimetry method with an auto-analyzer (Selectra 2, Vital Scientific, Spankeren, The Netherlands) using commercial kits (Pars Azmoon, Karaj, Iran). Low-density lipoprotein-cholesterol (LDL-C) was measured using a direct enzymatic method. The small-dense LDL-cholesterol content in plasma was quantitated according to the method described previously . Non-high density lipoprotein-cholesterol (Non-HDL-C) was calculated by subtracting HDL-C from total cholesterol. Plasma levels of complement C3 and C4 were determined using the turbidimetric method with commercial kits (Pars Azmoon, Karaj, Iran) using an auto-analyzer.
Dietary intakes and physical activity
Dietary intake and physical activity levels were monitored at baseline and after 6 weeks. Dietary intake was assessed using the 24-h dietary recall questionnaire completed in three days (two regular days in the middle of the week and one day on the weekend) by a trained dietitian. Participants were asked to maintain their habitual lifestyle throughout the study. Recall data was analyzed using the Nutritionist software (version IV, N-Squared Computing, San Bruno, CA, USA) to which was added the local food data.
Although the primary outcome was Lp-PLA2, sample size could not be calculated based on this variable, because according to our search, no study has compared the effects of CO and OO on Lp-PLA2 mass or activity. Nonetheless, studies have shown that Lp-PLA2 transported in plasma is predominantly (80%) associated with LDL-C . Therefore, the study sample size was calculated using LDL-C as the primary outcome variable. To detect a change in the mean of LDL-C concentration (10 mg/dL) as reported in a previous investigation  at the 5% level of significance and with 80% power, 24 participants were needed in each arm of the two-arm trial.
Data was analyzed using SPSS software for Windows version 21 (SPSS Inc., Chicago, IL, USA). All values were reported as mean ± SD or percentage (%). The per-protocol analysis was performed (i.e., only those who completed the study were included in the analyses). The normality of distribution of the study variables was tested by the Shapiro-Wilk test. When the variables were not normally distributed, raw values were log-transformed. Analysis of covariance (ANCOVA) was used to compare the 6-week values between the groups using the baseline measures as the covariate. Paired samples t‐test was used to compare the measurements in the beginning and at the end of the intervention within the study groups. The χ2 test was used to compare categorical variables. The statistical significance level was set at p = 0.05 (two tails).