This investigation was the cross-sectional study in which the celiac patients were randomly selected from the East-Azerbaijan, Iran CD registry database. The inclusion criteria were as follows: age 20-55 years old, diagnosis of celiac according to biopsy report, and following GFD for at least one year. All patients registered in the CD database. The patients who could not communicate with the interviewer or had other concomitant diseases were excluded.
As a general population, we used the data collected in the lifestyle promotion project (LPP) conducted in East Azerbaijan-Iran for the evaluation of lifestyle risk factors. We described the detailed method of participants' recruitment in our previous publication (13). For this study, the data of 462 healthy participants with the age of 20-55 years old were included in the statistical analysis. The participants with the known diabetes mellitus, CD or other diseases that affect their diet were excluded from the analysis.
The author-designed checklist was used for obtaining demographic characteristics. The same instruments were used for measuring weight (Seca weighing scale) and height (stadiometer fixed to the wall) in both celiac patients and the general population. Body mass index (BMI) was calculated by dividing weight (kg) to height (m2). A BMI of less than 18.5 was considered as underweight, 18.5-24.99 was normal weight, and ≥25 was overweight.
An expert dietitian has obtained the dietary intake of protein, Potassium, Magnesium, Phosphorus, and Calcium using a Semi-quantitative food frequency questionnaire (FFQ). The questionnaire was validated previously in the East-Azerbaijan population (14). For assessing the dietary intake of celiac patients, the gluten-free items were also added to FFQ. The Iranian modified Nutritionist IV software was used for the determination of protein and micronutrient content.
Dietary Acid Load scores estimation:
Three scores of dietary acid load including Net endogenous acid production (NEAP), Potential renal acid load (PRAL), and dietary acid load (DAL) were derived from estimations of several nutrient intakes :
- PRAL (mEq/day)= 0.49 x protein (g) + 0.037 x phosphorus (mg) – 0.021 x potassium (mg) – 0.026 x magnesium (mg) – 0.013 x calcium (mg)
- NEAP (mEq/day)= −10.2 + 54.5 (protein intake [g/d] ÷ potassium intake [mEq/d])
- DAL (mEq/day)= PRAL + (body surface area [m2] × 41 [mEq/day]/1.73 m2)
Body surface area was calculated using the following formula: 0.007184 × height0.725 × weight0.425
Assessing adherence to the CD:
Adherence to the GFD for CD participants was determined by the Persian version of the celiac disease adherence test. This questionnaire was previously validated in our population. Patients with a score of less than 13 were considered good adherents.
For statistical analyses, SPSS V 22 was used. Kolmogorov-Smirnov was used to verify the normality assumption. The independent t-test, chi-square, and Fisher exact tests were used for comparison of the general and anthropometric characteristics between groups. The one-way ANCOVA was used for comparing the dietary acid load scores between groups by adjusting to confounding factors such as age, sex, BMI, and energy intake. A significance level of 0.05 was used.