The present cross-sectional study done using data gathered in another multi-center epidemiological study conducted in Yazd city, Iran in early 2020. In that study, 48 public and private high schools selected from two educational districts using simple random sampling. Then, female and male students aged 13–14 years selected.
Because of schools, closure during COVID-19, pandemic, electronic questionnaires designed and placed in the virtual education groups of schools. All students asked to complete the online questionnaires, which comprised of GERD questionnaire (GERDQ), food frequency questionnaire (FFQ) and a questionnaire on demographic characteristics. Finally, out of 7214 adolescents 5141 completed the questionnaires with response rate of 71.3%. At the end, unacceptable responses were reviewed by telephone and corrected if it was required [35]. Written informed consent was obtained from all the participants and all parents.
Diagnosis of GERD
The GERD questionnaire is a tool for assessing GERD. It was composed of six items which four items evaluated positive symptoms of GERD included heartburn, sense of reflux, poor sleep and use of over-the-counter products and also two items assess negative situation for GERD considered nausea and epigastric pain [31]. Symptoms frequency responded during last week by participants. All positive symptoms of GERD scored 0, 1, 2, and 3
points for 0 day, 1 day, 2–3 days, and 4–7 days, respectively. Nausea and epigastric pain as negative symptoms scored 3, 2, 1, and 0 points for 0 day, 1 day, 2–3 days, and
4–7 days, respectively. Diagnosis of GERD was while the sum of scores calculated ≥ 8 [36].
Dietary intake assessment
Dietary intake of participants for a recent year was assessed by a validated FFQ [37]. The questionnaire assessed intake of food groups including meat, fish, potatoes, rice, total dairy, total fast food, total vegetables, fruits, legumes, wheat, barley, popcorn and pasta according to frequencies of "never", "weekly" and "every day". Participants categorized to tertiles according to MedDiet scores and then assessed dietary intakes.
The calculation of MedDiet scores
The MedDiet scores calculated based on the consumption reported for the following food groups: fruits, fish, vegetables, pulses, cereals, pasta, rice and potatoes considered as pro-Mediterranean foods and scored 0, 1 or 2 for eating of each item “never”, "weekly" and "every day", respectively. Meat, milk and fast food were considered as anti-Mediterranean foods and scores 2, 1, and 0 were assigned for “never”, "weekly" and "every day", respectively [38, 39]. The overall score calculated by summing the scores received for each item. Therefore, the overall MedDiet score ranged from 0 to 22.
Statistical analyses
General characteristics as well as dietary intakes across tertiles of MedDiet score expressed as means ± SD and numbers (percentage) for continuous variables and categorical, respectively. We used one-way ANOVA and chi-square test for assessing continuous and categorical variables across tertiles of MedDiet score, respectively. Binary logistic regression used to examine the association between adherence to MedDiet and GERD as well as its symptoms in the crude and multivariable adjusted models. Age and sex adjusted in model I. Other variables like watching TV and using computer and/or internet additionally adjusted in model II. In the model III body mass index (BMI) was also adjusted. All statistical analyses performed using the statistical package for social sciences (SPSS, version 21, IBM Corporation and USA). P-values less than 0.05 considered as statistically significant.