Low-FODMAP vs Gluten-Free Diet in Irritable Bowel Syndrome

Study Design This study was designed as a prospective, parallel-group, controlled clinical intervention trial. Patients presenting at the outpatient clinic were sequentially assigned to either a low-FODMAP or a gluten-free diet group.

Participants Inclusion criteria were: diagnosis of Irritable Bowel Syndrome according to Rome IV criteria, age between 18 and 65 years, literacy, and provision of written informed consent.

Exclusion criteria

included: psychiatric or neurological conditions affecting cooperation (e.g., dementia, psychosis); chronic conditions (celiac disease, inflammatory bowel disease, diabetes, chronic kidney failure, liver failure, malignancy); regular use of medication for IBS symptoms (antispasmodics, loperamide, laxatives, antidepressants); eating disorders (anorexia nervosa, bulimia nervosa); malabsorption syndromes preventing dietary adherence; and pregnancy or breastfeeding.

Data Collection Tools Gastrointestinal symptoms were assessed using the Gastrointestinal Symptom Rating Scale (GSRS). This scale comprises 15 items, each scored from 1 (no discomfort) to 7 (very severe discomfort), and includes five sub-dimensions: reflux (items 2 and 3), abdominal pain (items 1, 4, and 5), indigestion (items 6-9), diarrhea (items 11, 12, and 14), and constipation (items 10, 13, and 15). The Turkish validity and reliability study of the GSRS was conducted by Turan et al. (2017), with test-retest reliability coefficients ranging from 0.39 to 0.87 and a Cronbach's alpha coefficient of 0.82. The scale was self-administered at baseline (pre-test) and upon completion of the 4-week dietary intervention (post-test).

Dietary Interventions Patients were allocated to either the low-FODMAP or gluten-free diet group in order of presentation. All participants received individual dietary counseling from an experienced dietitian who was one of the study researchers.

Patients in the low-FODMAP diet group were advised to restrict foods high in FODMAPs (onions, garlic, pulses, certain fruits and vegetables, wheat products) and to choose low-FODMAP alternatives (rice, oats, potatoes, carrots, eggplant, bananas, etc.).

Patients in the gluten-free diet group were provided with a detailed diet plan excluding gluten-containing grains (wheat, barley, rye) and their derivatives (bread, pasta, pastries, biscuits), along with a list of naturally gluten-free foods (rice, corn, potatoes, meat, vegetables, fruits).

Both dietary interventions were applied over a 4-week period. Weekly telephone follow-ups were conducted by the research dietitian to assess adherence and address any issues.

Ethics Committee Approval Ethical approval was obtained from the Clinical Research Ethics Committee of Atatürk University, Erzurum (Meeting No. 9, Decision No. 50) on 31 October 2025. All participants received detailed information about the study procedures and provided written informed consent. Data confidentiality and integrity were maintained throughout the research, and the study was conducted in accordance with the revised principles of the Declaration of Helsinki.

Statistical Analysis Statistical analyses were performed using IBM SPSS Statistics 23. Normality was assessed using Kolmogorov-Smirnov and Shapiro-Wilk tests, Q-Q plots, and skewness/kurtosis measures, indicating non-normal distribution. Descriptive statistics were presented as frequency (n) and percentage (%) for categorical variables, and as mean ± standard deviation (SD) for continuous variables. The Pearson chi-square test was used for categorical comparisons, with Fisher's Exact Test applied when expected frequencies were below 5. Within-group comparisons (pre- vs post-diet) were performed using the Wilcoxon signed-rank test, while between-group comparisons of change scores were performed using the Mann-Whitney U test. A p-value of <0.05 was considered statistically significant.

Inclusion criteria

• Diagnosed with Irritable Bowel Syndrome (IBS) according to the Rome IV diagnostic criteria
• Aged between 18 and 65 years
• Literate
• Signed the informed consent form

Exclusion criteria

• Psychiatric or neurological condition affecting cooperation (dementia, psychosis, etc.)
• Chronic condition (celiac disease, inflammatory bowel disease, diabetes, chronic kidney failure, liver failure, malignancy)
• Regular use of medication for IBS symptoms (antispasmodics, loperamide, laxatives, antidepressants, etc.)
• Eating disorder (anorexia nervosa, bulimia nervosa, etc.)
• Malabsorption syndrome preventing adherence to the diet
• Pregnancy or breastfeeding