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.