This cross-sectional study was performed within the framework of the Study on the Epidemiology of Psychological, Alimentary Health, and Nutrition (SEPAHAN) in Iran. This project was a community-based plan designed to investigate the epidemiological impressions of functional gastrointestinal disorders (FGIDs) and their association with mental and lifestyle determinants on non-academic members of Isfahan University of Medical Sciences. SEPAHAN was conducted in 2010 in two separate waves. Briefly, 10087 non-academic members of the staff of Isfahan University of Medical Sciences (IUMS), who were working in hospitals, university campus, and health centers affiliated with IUMS, were invited to participate in the first study. The first phase focused on evaluating the basic characteristics, lifestyle, and dietary habits, and intakes of participants. The response rate in this phase was 86.16%, and 8691 completed questionnaires were returned. At the second phase, other questionnaires, which were designed to collect information on gastrointestinal, psychological, and somatoform symptoms, were distributed and 6239 completed questionnaires were returned (response rate: 64.64%). After merging data from these two phases, complete information was available for 4763 people. Ethics Committee of the University of Medical Sciences has approved the protocol of the study (Project numbers: #189069, #189082, and #189086), and written informed consent was obtained from all participants after clarifying the protocol. The details about the design, conducting, instruments, and all aspects of study could be found elsewhere (Adibi, Keshteli, et al. 2012).
2.2.1. Assessment of eating speed
The eating speed was investigated by using a questionnaire that included the following questions: ‘how thoroughly do you chew foods? (Not very well, well, very well)’, ‘how long does it take you to eat lunch? (never eat lunch, < 10 min, 10–20 min, > 20 min)’, ‘how long does it take you to eat dinner? (never eat dinner, < 10 min, 10–20 min, > 20 min)’. We applied Latent class analysis to determine classes of people in terms of their eating speed (Hagenaars, Mccutcheon, 2002). All questions, provided in Table 1, were variables that entered into LCA. Eating speed was considered as a latent construct that could not be examined directly. Therefore, LCA as an advanced statistical method was used for the extracting of the eating speed habit indirectly based on the series of eating speed variables. Eating speed was assessed using LCA by examining the pattern of relations between observed eating speed variables and classifying individuals with similar profiles (i.e., latent classes). Therefore, each constructed class plays a role in a specific level of eating speed. In this analysis, different indicators of eating rate described in Table 1, were examined. During LCA fitting to the data, at first, a one-class model was applied. Then, we sequentially increased the number of latent classes to determine the most parsimonious and interpretable model. For example, since a high percentage of subjects responded that they would chew meals more than 20min, such a pattern of eating rate was considered as normal eating rate class and when the majority of people expressed their chewing duration of each meal as "lower than 10min" the related class was considered as speedy. Finally, based on the mentioned questions, using latent class analysis (LCA) eating speed was defined as three classes: ‘normal’, ‘relative speedy’ and ‘speedy (Saneei, P et al. 2016)
2.2.2. Assessment of personality traits
The big five personality inventory short form was used to evaluate personality traits. The five factors include Neuroticism (N): the tendency to experience affective instability (hostility, anxiety, depression, angry, vulnerability, and impulsivity) and negative affect; Extraversion (E): dispositions toward sociability and energetic activity (assertiveness, positive emotion, warmth, gregariousness, seeking, and excitement); Openness (O): reflects individual's like interest in novel people, and ideas, as well as esthetic and intellectual propensities (values, feelings, fantasy); Agreeableness (A): a propensity toward amiability, (modesty, trust, altruism, compliance, and straightforwardness); and Conscientiousness (C): qualities such as fastidiousness, goal-orientation, and dependability (order, self-discipline, competence, achievement striving, and deliberation) (Chapman B et al.2007). These factors include the principal axes of behavioral and psychological variations in people and each element is associated with several prominent health-related behaviors and outcomes, which contain higher levels of overall morbidity and self-rated health (Neeleman J et al. 2002). This 60-item scale consists of 12 items for each subscale. These items are scored from one to five. One is for strongly disagree, and five for strongly agree. Some items are reverse scored. Higher scores point to higher levels of that particular personality trait. The reliability of the entire scale (α = 0.70) and subscales (αs > 0.68), and the internal consistency of the subscales in Iranian have been established previously(Anisi, Majdiyan, et al. 2011).
2.2.3. Assessment of other variables
A self-administered questionnaire was used to gather information on age, sex, educational attainment (less than diploma (12-year formal education), diploma, and university graduate), smoking habits (current smoker, never smoking, ex-smoker), marital status (single, married), body weight and height of the participants and BMI (kg/m2). The general physical activity questionnaire (GPAQ) was used to assess their physical activity(Physical activity levels of participants were categorized as never, less than 1 hour, 1–3 hour, and more than 3 hours per week) (Ahmad, Harris, et al. 2015). The reliability of this questionnaire was assessed using Cronbach's alpha coefficient (α = 0.84). The functional gastrointestinal disorders (FGIDs) were defined as suffering from at least one of the following: irritable bowel syndrome (IBS), gastroesophageal reflux disorder (GERD), constipation, and dyspepsia. FGIDs were determined using a modified Persian version of the Rome III questionnaire (The split-half test reliability of whole items value was 0.72), as a section of the main comprehensive questionnaire and Talley Bowel Disease Questionnaire (TALLEY, PHILLIPS, et al. 1990, Toghiani et al.2016). Psychological distress was assessed by using the validated Iranian version of the General Health Questionnaire-12 (GHQ) and classified as no psychological distress and presence of psychological distress. Reliability analysis showed satisfactory results (Cronbach's alpha coefficient = 0.87) (Montazeri, Harirchi, et al. 2003).
2.2.4. Statistical analysis
Participants were categorized into three groups based on the eating speed behavior using latent class analysis (‘normal’, ‘relative speedy', and 'speedy’). To determine significant differences in demographic characteristics, personality traits, lifestyle variables, and gastrointestinal disorders, and psychological distress across categories of eating speed, we used analysis of variance (ANOVA) and chi-square test for continuous and categorical variables, respectively. Odds ratios (OR), and 95% confidence intervals (CIs) for eating speed as dependent variable across quartiles of different personality traits scores were calculated using logistic regression in crude and adjusted models. Model 1 was adjusted for age, sex, marital status, educational level. Additional adjustments for BMI, smoking, and physical activity were made in model 2. Model 3 was additionally adjusted for FGIDs and psychological distress. P for linear trend was determined by considering the frequency of eating speed as linear continuous variables in the logistic regression model. Holm-Bonferroni method (Hommel, G,1988) was used to adjust the type one error rate for multiple comparisons, and adjusted p-value thresholds for significance were reported in tables. P < 0.05 was considered as a statistical significance (2-sided) level.