The SEPAHAN project (Epidemiology of Psychological, Alimentary Health and Nutrition) was used as a source of data for this cross-sectional study . The project mainly aimed to find out whether lifestyle and psychological factors have an association with functional GI disorders in adults (18–55 years) in Isfahan province. The SEPAHAN project included non-academic staff, managers and their socio-economic status, and employees who were working in fifty healthcare centers affiliated with Isfahan University of Medical Sciences (IUMS). Isfahan University of Medical Sciences' Bioethics Committee approved the project protocol (Approval No. 189069, 189082, and 189086). All subjects filled out a written informed consent form before participating. A total of 10,087 subjects distributed to complete self-administered questionnaires in phase one of the project, which collected sociodemographic data, anthropometric measurements, medical history, physical activity levels, and dietary intake data. A response rate of 86.16% to the questionnaires was recorded in this phase and 8.691 subjects completed the questionnaires. In the second phase, participants were asked to fill out the questionnaire about gastrointestinal profile. 64.6% of participants provided information about GI health (N = 6239). As a result of combining the data from both phases, we had information on 4,763 subjects' dietary intakes and GI disorders from phase one and tow. Finally, we excluded participants in the final analyses if their daily energy intakes were lower than 800 kcal/d or upper than 4200 kcal/d. After this exclusion 3,362 participants remain for the final analysis.
Dietary Intakes Assessment And Dtac Calculation
We gathered dietary intakes of the study participants using a validated 106-items dish-based semi-quantitative food frequency questionnaire (DS-FFQ) . The DS-FFQ included five categories of food and dishes, including mixed dishes (canned or cooked, 29 items), grains (different kinds of breads, potatoes, cakes, and biscuits, 10 items), fruits and vegetables (22 items), dairy products (dairies, cream, and butter, 9 items), and miscellaneous food items and beverages (including beverages, fast foods, sweets, nuts, and desserts, 36 items). To collect information about these 106 food items, we defined a routine portion size for each and subjects reported their amount of consumption based on nine multiple-choice frequency response categories which were varied from “never or < 1/month” to “≥ 12/day”. Accordingly, 6 to 9 options were available for frequency responses. For foods consumed rarely, we removed the high-frequency category, while we added several multiple-choice categories for foods consumed frequently. According to the frequency of consumption of each food item, grams of each food item were estimated based on household measurements. The ferric-reducing antioxidant power (FRAP) (mmol/100 g) values of each food item in the DS-FFQ were used to calculate DTAC. The FRAP assay is used to measure the ability of total anticipants in a diet that reduces ferric ions to ferrous ones . Accordingly, we calculated the FRAP values for foods based on the previous research . In the case of food items that were similar (e.g., a variety of breads, meats, etc.) or did not have available FRAP values, the values of nearest comparable food were assigned. Then, each frequency consumption for each food item was multiplied by its FRAP value and all summed to obtain dTAC for each person.
Assessment Of Ibs
A version of the Rome III questionnaire, which was developed for the Iranian population, was utilized to measure IBS symptoms. . Because most participants found it difficult to respond to an original questionnaire (never, 1 day per month, 1 day per month, 2–3 days per month, 1 day per week, more than 1 day per week, and every day), we used a questionnaire with a 4-item rating scale (never/rarely, sometimes, often, and always). Each symptom's long-term experience (six months or more) was replaced with a shorter-term experience (less than three months) . Subjects has IBS if they experienced abdominal discomfort or pain before the initiation of study sometimes (in the last three months) along with at least two or more of the following criteria; improvement in abdominal discomfort or pain with defecation sometimes and the onset of such condition related to changes in stool frequency or form . Constipation-predominant IBS was identified if they had hard or lumpy stools, as well as a lack of loose, mushy, or watery stools. . If they had watery stools and no firm stools on a regular basis, they had diarrhea-predominant IBS . The subjects were considered to have mixed IBS if they had IBS, hard or lumpy stools at least sometimes, and loose, mushy, or watery stools at least sometimes . Other participants were considered as unshaped kind of IBS. The severity of abdominal pain in the last three months was also reported by the subjects and classified as mild, moderate, severe, and very severe.
Assessment Of Other Lifestyle Factors
We collected information on other lifestyle factors such as age, sex, smoking history, marital status, medication use, and disease history through a self-reported questionnaire. A number of anthropometric measurements were taken, including weight, height, and waist circumference and Body mass index (BMI) was estimated by dividing of weight in kg by height in square of meter (kg/m2). A pilot study on a sample of 200 participants found reasonable results for the usefulness of these self-reported anthropometric measures. The results showed statistically significant correlation coefficient for weight 0.95 (P < 0.001), height 0.83 (P < 0.001), WC 0.60 (P < 0.001), and BMI 0.70 (P < 0.001) from these self-reported values compared to the measured values . The General Practice Physical Activity Questionnaire (GPPAQ) was also completed by the subjects to assess physical activity levels. Accordingly, subjects were classified as physically inactive (< 1 h/week) and physically active (≥ 1 h/week). Also, intra-meal fluid intake (< 3 glasses/≥3 glasses), meal regularity (often or frequently or always and never or rarely), and chewing efficiency (a lot/not a lot) were evaluated through a pretested questionnaire. The subject’s dental status was assessed based on four different categories (“fully dentate”, “lost 1–5 teeth”, and “lost > 5 teeth”). Finally, we gathered information on dietary supplement usage (yes/no), oral contraceptives drugs usage (yes/no), and the presence of colitis (yes/no).
In this study, we classified participants according to tertile cut-off points of dTAC score. One way ANOVA and chi-square tests were used to compare the differences of general characteristics of participants across tertiles of dTAC. We used the analysis of covariance (ANCOVA) test for comparison of energy-adjusted dietary intakes of participants across tertiles of dTAC. A binary logistic regression test was used to estimate odd ratios and 95% CIs of IBS and its subtypes across tertiles of dTAC in crude and multivariable-adjusted models. In the analyses, models were adjusted for age, sex, energy intake, marital status, education, BMI, physical activity, diabetes history, medication use, smoking, meal regularity, dietary supplements use, chewing sufficiency, frequency of fried food consumption, speed of eating, dental status, intra-meal fluid consumption, and breakfast skipping). We also estimated ORs and 95% CIs for IBS severity (mild, moderate, severe, and very severe) across tertiles of dTAC multivariable ordinal logistic regression. SPSS software (version 24; SPSS Inc.) was used for data analysis and P < 0.05 was considered as statistically significant.