Effectiveness of Low FODMAPs Diet Compared With Standard Dietary Advice in Functional Dyspepsia

Functional dyspepsia is a common digestive disorder that causes symptoms such as feeling unusually full after eating, early fullness during meals, bloating, and pain or discomfort in the upper abdomen. Many people with functional dyspepsia continue to have symptoms despite standard treatment. Dietary factors may contribute to symptoms, and a low-FODMAP diet may be helpful for some patients. FODMAPs are types of carbohydrates that are poorly absorbed in the small intestine and can be fermented by intestinal bacteria, which may contribute to gastrointestinal symptoms.

This randomized controlled study will evaluate whether a 4-week low-FODMAP dietary intervention improves symptoms in adults with functional dyspepsia compared with standard dietary advice.

Participants will be adults aged 18 to 70 years with functional dyspepsia diagnosed according to the Rome IV criteria. Participants must have had a normal upper gastrointestinal endoscopy within the previous 6 months and negative testing for Helicobacter pylori infection. Eligible participants will have predominantly postprandial distress syndrome (PDS), with or without overlapping epigastric pain syndrome (EPS), and moderate-to-severe symptoms.

Participants will be excluded if they have irritable bowel syndrome, significant organic gastrointestinal disease, active systemic malignancy or severe systemic illness, a current or previous eating disorder, clinically significant malnutrition, pregnancy, or breastfeeding. Participants who are currently following a low-FODMAP diet or another restrictive diet that substantially changes fermentable carbohydrate intake will also be excluded. Recent use of antibiotics, probiotics, or medications that may substantially affect gastrointestinal motility or the gut microbiota will also be considered according to the study eligibility criteria.

Before enrollment, eligible participants will receive verbal and written information about the study, including its purpose, procedures, potential risks and benefits, and participant responsibilities. Written informed consent will be obtained before any study-related procedures are performed. Participation will be voluntary, and participants may withdraw from the study at any time without giving a reason and without affecting their usual medical care.

At baseline, demographic and clinical information will be collected. Functional dyspepsia symptoms will be assessed using the Patient Assessment of Gastrointestinal Disorders-Symptom Severity Index (PAGI-SYM). Participants will also complete a 7-day food diary before randomization. A registered dietitian will use standardized nutritional analysis software to estimate baseline FODMAP intake.

Participants will then be randomly assigned using a computer-generated randomization sequence to one of two groups:

1. \*\*Standard dietary advice group:\*\* Participants will receive standardized verbal and written dietary advice for functional dyspepsia from a physician.
2. \*\*Low-FODMAP dietary advice group:\*\* Participants will receive the same standard dietary advice plus structured low-FODMAP dietary counseling from a registered dietitian.

The dietary intervention will last 4 weeks. Participants in the low-FODMAP group will receive guidance on reducing foods high in FODMAPs during the restriction phase. Dietary counseling will be provided to support understanding of the diet and adherence to the intervention.

Functional dyspepsia symptoms will be assessed at baseline and weekly throughout the 4-week intervention using the PAGI-SYM questionnaire. Participants will also record their food intake and bowel movements each week using the Bristol Stool Form Scale. These records will be used to evaluate changes in dietary intake, gastrointestinal symptoms, and bowel habits during the study.

Adherence to the low-FODMAP intervention will be assessed by comparing estimated daily FODMAP intake during the intervention with baseline intake. Participants in the low-FODMAP group will be considered compliant if their estimated daily FODMAP intake is reduced by at least 50% compared with baseline.

The main purpose of the study is to determine whether the low-FODMAP dietary intervention results in greater improvement in functional dyspepsia symptoms compared with standard dietary advice. Changes in PAGI-SYM scores over the 4-week intervention will be evaluated between the two groups. Changes in dietary intake and bowel habits will also be assessed.

Safety will be monitored throughout the study. Participants will be asked about adverse events and any symptoms or side effects that may be related to dietary modification. Any relevant adverse events will be recorded and managed according to standard clinical practice.

The study is expected to provide information about whether a short-term low-FODMAP dietary intervention may be a useful dietary approach for adults with functional dyspepsia, particularly those with predominantly postprandial symptoms.

Participants will receive standardized verbal and written dietary advice for functional dyspepsia provided by a physician. They will continue their usual diet while following the general dietary recommendations. Symptoms, food intake, and bowel movements will be recorded throughout the 2-week study period.

Behavioral: Standard dietary advice

Participants will receive the same standard dietary advice as the control group, plus structured low-FODMAP dietary counseling provided by a registered dietitian. Participants will follow the low-FODMAP diet for 2 weeks. Dietary intake, symptoms, and bowel movements will be recorded throughout the intervention period. Adherence will be assessed by comparing estimated daily FODMAP intake with baseline intake.

Behavioral: Low Fodmap dietary advice

Participants assigned to the intervention arm will receive standard dietary advice for functional dyspepsia plus structured low-FODMAP dietary counseling provided by a registered dietitian. The intervention will last 2 weeks and will focus on reducing dietary intake of fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs). Participants will receive verbal and written dietary guidance and will record their food intake throughout the intervention. Dietary adherence will be assessed by comparing estimated daily FODMAP intake during the intervention with baseline intake. Participants will complete weekly PAGI-SYM assessments and record bowel movements and any adverse effects.

Participants assigned to the control group will receive standardized verbal and written dietary advice for functional dyspepsia provided by a physician. They will not receive specific low-FODMAP dietary counseling and will continue their usual diet while following the general dietary recommendations. The intervention will last 2 weeks. Participants will complete weekly PAGI-SYM assessments and record their food intake, bowel movements, and any adverse effects during the study period

Time frame: 2 weeks

The severity of functional dyspepsia symptoms will be assessed using the Patient Assessment of Gastrointestinal Disorders-Symptom Severity Index (PAGI-SYM), which consists of 20 items scored on a 6-point Likert scale from 0 (none) to 5 (very severe). The total score ranges from 0 to 5 when calculated as the mean of the item scores, with higher scores indicating greater symptom severity and worse outcomes. The change in mean symptom score from baseline to the end of the 2-week intervention will be compared between the low-FODMAP and standard dietary advice groups.

Minimum score is 0, maximum score is 80

Time frame: 2 weeks

Change in the number of high-FODMAP food items consumed, assessed by reviewing participants' food diaries and counting reported high-FODMAP food items at baseline and during the intervention. The change from baseline to the end of the 2-week intervention will be compared between the low-FODMAP and standard dietary advice groups.

Time frame: 2 weeks

Change in stool consistency measured using the Bristol Stool Form Scale (BSFS), a 7-point scale ranging from 1 (separate hard lumps) to 7 (watery stool). Higher scores indicate looser stool consistency (worse outcome in terms of stool consistency). Bowel habits, including bowel movement frequency, will be assessed separately using the daily bowel diary.

Time frame: 2 weeks

Change in health-related quality of life from baseline to Week 2, assessed using the EuroQol 5-Dimension 5-Level (EQ-5D-5L) questionnaire. The EQ-5D-5L descriptive system assesses five dimensions of health, each with five response levels. The EQ-5D-5L index value will be calculated using the appropriate value set, with higher index values indicating better health-related quality of life.

Effectiveness of Low FODMAPs Diet Compared With Standard Dietary Advice in Functional Dyspepsia