Materials and Methods

Subjects

This hospital based case-control study carried out in Shiraz, Iran. For this, 125 men (62 cases and 63 controls), who were referred to two main hospitals (teaching and referral hospitals) in Shiraz, Iran were recruited. To collect required information such as general characteristics and dietary intakes, the patients were interviewed by trained interviewers during their hospital stay Patients with PC who were candidate for radical or open prostatectomy were selected as cases based on the following inclusion criteria: persons without any history of dietary regimens for chronic diseases, diabetes, or other types of cancers and who their diseases were diagnosed maximum one month after diagnosis. At the same time, controls were selected from the patients who came to the same hospitals due to non-neoplastic, non-diabetic conditions including eye, gastrointestinal, ear, nose, and throat (ENT), kidney, and nerve diseases. Similar to the cases, the controls also did not follow any dietary regimens for chronic diseases. Cases and controls were matched for body mass index (<19, 19–25, 25–30, 30<kg/m2) and age (within strata of 5-year age groups). Total energy intakes of <800 or >4200 kcal/day and poor response to food frequency questionnaire considered as exclusion criteria. This research was approved by the ethic committee of Shiraz University of medical sciences and all participants provided informed consent (93-01-21-9059).

Demographic and Anthropometric Assessment

Demographic characteristics of participants including: smoking habit, physical activity level, ethnicity, job, education, and some medications usage were recorded using a general questionnaire via face to face interview. Weight was measured by a digital scale with a precision of 0.1 kg (Glamor BS-801, Hitachi, China), while individuals wore light clothing and no shoes. Height was measured at 0.1 cm precision in a standing position without shoes, using a non-stretchable tape. Body mass index (BMI) was calculated as weight in kilograms divided by height in meters squared.

Dietary intake assessment and estimation of dietary acid load

Dietary intakes were assessed using a semi-quantitative food frequency questionnaire (FFQ) (36-38). This questionnaire included 160 common food items which are common among Iranian population. Accordingly, the frequency of consumption of each food item was divided in nine categories: “never or less than once a month”, “1 to 3 times a month”, “once a week”, “2 to 4 times a week”, “5 to 6 times a week”, “once a day”, “2 to 3 times a day”, “4 to 5 times a day”, and “6 times or more a day”. In addition, the portions were classified in three sizes including: small (half of the defined average use or less), medium (equal to the defined average use), and large (one and half of the defined average use or more). The FFQs were analyzed using a specific multifunction software which developed by Borland Delphi 7 (http://www.embarcadero. com/products/delphi) and Visual Basic 2008 (VB 9.0) (http://www.microsoft.com/visualstudio/eng/ products/visual-studio-express-products). Daily intakes of energy, macronutrients, and micronutrients were derived using the Nutritionist 4 software. We used the PRAL and NEAP (indicators of dietary acid load) for estimation of dietary acid load. These indexes were calculated based on the previous published equation:
NEAP (mEq/day) = 54.5 × protein (g/day)/potassium (mEq/ day) − 10.2 [10]. PRAL (mEq/day) = 0.4888 × protein intake (g/day) + 0.0366 × phosphorus (mg/day) − 0.0205 × potassium (mg/day) − 0.0125 × calcium (mg/day) − 0.0263 × magnesium (mg/day)(39).

Statistical Analysis

The normality of the data was assessed using Kolmogorov-Smirnov test. Categorical variables presented as percent, and continuous variables presented as mean ± SD. One-way analysis of variance (ANOVA) test and Chi-square or Fischer exact tests were used for comparison quantitative and qualitative variables respectively, across tertiles of PRAL and NEAP scores. Dietary intakes of participants across tertiles of PRAL and NEAP scores were compared using analysis of covariance (ANCOVA) test and presented as mean ± SE. To assess risk of prostate cancer in relation to PRAL and NEAP, Multivariate logistic regression was used. In adjusted models, age, body mass index, energy intake, smoking, physical activity, ethnicity, job, education, and drug usage were controlled. Statistical analyses were performed using SPSS software (version 23, SPSS Inc., Chicago, IL, USA). P<0.05 was considered statistically significant.