Low-FODMAP vs Lactose-Gluten-Free Diet in Patients With Irritable Bowel Syndrome

Comparative Effects of Low-FODMAP and Lactose-Gluten-Free Diets on Gastrointestinal Symptoms and Mental Health in Irritable Bowel Syndrome: A Randomized Crossover Trial

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder that substantially affects quality of life. Dietary therapy is considered one of the primary treatment approaches; however, the optimal sequence of dietary interventions remains unclear. This randomized crossover trial was designed to compare the effects of a low-FODMAP diet and a lactose-free, gluten-free diet on gastrointestinal symptoms, psychological status, anthropometric measurements, and biochemical parameters in adults with IBS. Participants were randomly assigned to one of two dietary sequences, with each intervention lasting four weeks and separated by a one-week washout period. Outcomes were assessed using validated symptom and psychological questionnaires together with anthropometric and biochemical measurements before and after each intervention period.

Study Overview

• Status: Completed
• Conditions: Irritable Bowel Syndrome
• Intervention / Treatment: Behavioral: Low-FODMAP Diet; Behavioral: Lactose- and Gluten-Free Diet

Detailed Description

This randomized crossover trial was designed to evaluate the comparative effects of a low-FODMAP diet and a lactose- and gluten-free diet in adults with irritable bowel syndrome (IBS). Participants were randomly assigned to one of two dietary sequences, with each intervention lasting 4 weeks and separated by a 1-week washout period. Gastrointestinal symptoms, psychological outcomes, anthropometric measurements, and biochemical parameters were assessed before and after each intervention period.

• Study Type: Interventional
• Enrollment (Actual): 72
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Turkey (Türkiye)
  • Istanbul, Turkey (Türkiye)
    • Istanbul University-Cerrahpaşa, Cerrahpaşa Faculty of Medicine, Department of Gastroenterology

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Adults aged 18-64 years.
• Diagnosis of Irritable Bowel Syndrome according to the Rome III criteria.
• Ability and willingness to comply with the dietary intervention.
• Written informed consent provided.

Exclusion Criteria:

• Pregnancy or lactation.
• Diabetes mellitus.
• Organic gastrointestinal disease.
• Current follow-up for cardiologic, neurologic, oncologic, or psychiatric disorders.
• Following a therapeutic diet within 1 month before enrollment.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Low-FODMAP → Lactose- and Gluten-Free Diet; Participants received the low-FODMAP diet for 4 weeks, followed by a 1-week washout period and then the lactose- and gluten-free diet for 4 weeks.	Behavioral: Low-FODMAP Diet; Participants followed a low-FODMAP diet for 4 weeks under the supervision of a dietitian.; Behavioral: Lactose- and Gluten-Free Diet; Participants followed a lactose- and gluten-free diet for 4 weeks under the supervision of a dietitian.
Experimental: Lactose- and Gluten-Free Diet → Low-FODMAP; Participants received the lactose- and gluten-free diet for 4 weeks, followed by a 1-week washout period and then the low-FODMAP diet for 4 weeks.	Behavioral: Low-FODMAP Diet; Participants followed a low-FODMAP diet for 4 weeks under the supervision of a dietitian.; Behavioral: Lactose- and Gluten-Free Diet; Participants followed a lactose- and gluten-free diet for 4 weeks under the supervision of a dietitian.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Irritable Bowel Syndrome Symptom Severity Score (IBS-SSS)	Change in Irritable Bowel Syndrome Symptom Severity Score (IBS-SSS). The IBS Symptom Severity Score assessed the severity of IBS symptoms based on four questions, scoring between 0 and 100 points for each symptom. A total score of 75-174 points indicated mild IBS, 175-299 points indicated moderate IBS, and >300 points indicated severe IBS.	Baseline, Week 4, and Week 9

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Gastrointestinal Symptom Rating Scale (GSRS) score	Change in gastrointestinal symptom severity assessed using the Gastrointestinal Symptom Rating Scale (GSRS). The GSRS assessed gastrointestinal symptoms based on 15 items categorized into five subdimensions: abdominal pain, reflux, diarrhea, indigestion, and constipation. The scale measures symptom severity over the past week, with higher scores indicating more severe symptoms.	Baseline, Week 4, and Week 9
Change in Hospital Anxiety and Depression Scale (HADS) score	Change in anxiety and depression symptoms assessed using the Hospital Anxiety and Depression Scale (HADS). The HADS is a 14-question scale that identifies anxiety and depression risks. The scale is divided into two subscales, one for anxiety and one for depression, with scores ranging from 0 to 21. Scores between 0-7 are considered normal, 8-10 borderline, and ≥11 indicates anxiety and/or depression.	Baseline, Week 4, and Week 9
Change in body weight	Change in body weight measured in kilograms.	Baseline, Week 4, and Week 9
Change in body mass index	Change in body mass index (BMI), calculated as weight in kilograms divided by height in meters squared.	Baseline, Week 4, and Week 9

Collaborators and Investigators

• Sponsor: Antalya Bilim University
• Investigators: Principal Investigator: Hatice Kübra Aras, Antalya Bilim University

Study record dates

Study Major Dates

• Study Start (Actual): September 1, 2020
• Primary Completion (Actual): November 25, 2021
• Study Completion (Actual): January 20, 2022

Study Registration Dates

• First Submitted: July 16, 2026
• First Submitted That Met QC Criteria: July 21, 2026
• First Posted (Actual): July 23, 2026

Study Record Updates

• Last Update Posted (Actual): July 23, 2026
• Last Update Submitted That Met QC Criteria: July 21, 2026
• Last Verified: July 1, 2026

More Information

Terms related to this study

• Keywords: Irritable Bowel Syndrome; Anxiety; Diet; FODMAPs; Lactose-free and gluten-free diet
• Additional Relevant MeSH Terms: Mental Disorders; Intestinal Diseases; Digestive System Diseases; Gastrointestinal Diseases; Colonic Diseases; Colonic Diseases, Functional; Irritable Bowel Syndrome; Anxiety Disorders; Therapeutics; Diet, Food, and Nutrition; Physiological Phenomena; Carbohydrates; Nutritional Physiological Phenomena; Diet Therapy; Nutrition Therapy; Diet; Polysaccharides; Disaccharides; Oligosaccharides; Sugars; Elimination Diets; FODMAP Diet; Diet, Gluten-Free; Lactose
• Other Study ID Numbers: 2020/034

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No