Trial Review

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Trial registered on ANZCTR


Registration number
Help: Registration number
ACTRN12626000712303
Ethics application status
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Approved
Date submitted
Help: Date submitted
30/03/2026
Date registered
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15/06/2026
Date last updated
Help: Date last updated
15/06/2026
Date data sharing statement initially provided
Help: Data sharing statement date
15/06/2026
Type of registration
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Prospectively registered

Titles & IDs
Public title
Dietary intervention for gut and mental health symptoms in irritable bowel syndrome.
Scientific title
DUAL Study - Effectiveness of dietary intervention for gut and mental health symptoms in irritable bowel syndrome.
Additional trial identifiers [1] 316821 0
Nil known
Universal Trial Number (UTN)
Trial acronym
Related trial records

Health condition
Health condition(s) studied:
Irritable Bowel Syndrome 341170 0
Anxiety 341171 0
Depression 341509 0
Condition category
Condition code
Diet and Nutrition 337262 337262 0 0
Other diet and nutrition disorders
Oral and Gastrointestinal 337587 337587 0 0
Other diseases of the mouth, teeth, oesophagus, digestive system including liver and colon
Mental Health 338406 338406 0 0
Anxiety
Mental Health 338407 338407 0 0
Depression

Intervention/exposure
Study type
Interventional
Description of the intervention or exposure
This is a parallel-design, blinded, randomised controlled trial. There will be 2 dietary arms, each administered for 8 weeks. Participants will be randomly allocated to either the traditional Mediterranean Diet (MedDiet; active arm) or a Sham Diet (placebo arm), with the primary objective of measuring differences in gastrointestinal symptom response between groups at week-8 follow-up, defined as a 50 point improvement in the IBS Symptom Severity Scale (IBS-SSS) or greater.

The intervention diet (MedDiet) is characterised by a high intake of plant-based foods including olive oil, fruits, vegetables, nuts and seeds, and wholegrains; moderate intake of fish and poultry; and a low intake of dairy products, red meat, processed meats, and sweets. For those who already consume alcohol, optional red wine in moderation (no more than 100mL per day), consumed with meals, is permitted. Participants following the MedDiet will be guided by specific daily and weekly food and food group targets, alongside foods to avoid or limit. The traditional MedDiet guidelines are based off of those previously used in IBS research (see https://doi.org/10.1111/apt.17791).

The intervention diet will be administered through dietary counselling (see below for visit schedule). Participants will receive tailored dietary guidance from the research dietitian at each dietitian consultation to support compliance with their allocated diet for the duration of the intervention. Dietitian sessions will also integrate behaviour change techniques such as goal setting and motivational interviewing. The Dietitian sessions will be supported by behaviour change resources including purpose-designed written materials (e.g., recipes and meal planning resources developed for this study) and a food hamper provided once within the first week of the study. The hamper contains core ingredients to support adherence to the allocated diet, including foods from key MedDiet food groups such as olive oil, nuts, and seeds. As hamper contents may vary seasonally, the specific items included may differ between participants but will remain consistent with the principles of the allocated study diet.

The study will include 5 scheduled study visits across the 8-week intervention period with a research dietitian. All visits will be conducted remotely via telephone or online consultation. At Baseline, participants will complete a 45-minute dietary consultation with the study dietitian, alongside online questionnaires assessing gastrointestinal symptoms, mental health symptoms, and quality of life, as well as a three-day food record. Subsequent visits at Weeks 2, 4, and 6 will each involve a 30-minute dietary consultation and online questionnaires assessing dietary adherence, with the Week 4 visit also including reassessment of gastrointestinal symptoms, mental health symptoms, and quality of life. The final visit at Week 8 will include a 30-minute dietary consultation and completion of online questionnaires covering gastrointestinal symptoms, mental health symptoms, quality of life, dietary adherence, and an end-of-intervention survey.

Dietary adherence to the allocated study diet will be monitored throughout the study via self-reported questionnaires administered at fortnightly intervals corresponding with dietitian visits. Adherence to the Mediterranean Diet will be assessed at baseline and week 8 using the Mediterranean Diet Adherence Screener (MEDAS).
Intervention code [1] 333507 0
Lifestyle
Intervention code [2] 333859 0
Treatment: Other
Description of the comparator or control
The control is a Sham (placebo) diet. Participants will be informed that the study is investigating the effect of two different dietary patterns on gastrointestinal and mental health symptoms. Participants will be informed that neither they nor the lead researcher will know which dietary pattern they have been allocated to until the results have been analysed. They will also be informed that to maintain the integrity of the study design and findings, they will not be informed of the name of the diet until the analysis has been completed.

The Sham diet has been designed specifically for this trial based on the following criteria: (1) it is a convincing placebo diet to maintain blinding (i.e., will contain distractors), (2) it avoids modifying intake of nutrients (e.g., fibre) of the MedDiet or dietary constituents that might impact gut or psychological symptoms (e.g., FODMAPs), (3) it imposes an equivalent participant and dietitian burden for implementation, and (4) it is feasible to follow. Other contextual effects such as patient-provider interaction and placebo effects related to the setting will also be kept consistent across groups. Therefore, the Sham diet is designed to address both dietary and contextual factors which may influence study outcomes.

The Sham diet follows the structure of the New Zealand Eating and Activity Guidelines as a foundation, where four core food groups (fruit and vegetables, grains and cereals, protein foods, and dairy and alternatives) contribute the bulk of an individual's dietary intake, whilst also considering habitual intakes of these core food groups from the latest New Zealand National Nutrition Survey. The Sham diet has been internally validated within the research team and is successful in not modifying intake of key nutrients of the MedDiet (fibre, unsaturated fatty acids) or other dietary constituents (e.g., FODMAPs) which may impact gut or psychological symptoms, and is a safe and adequate diet to follow.

Delivery of the Sham diet will mirror that of the MedDiet to ensure equivalent participant and dietitian burden across groups. Participants will receive tailored dietary guidance from the study dietitian across five remote consultations (via telephone or online) over the 8-week intervention period, comprising a 45-minute baseline consultation followed by 30-minute consultations at Weeks 2, 4, 6, and 8. Dietary adherence will be monitored via self-reported questionnaires administered fortnightly at each dietitian visit. Participants will also receive purpose-designed written resources specific to the Sham diet (e.g., recipes and meal planning resources) and a food hamper provided once within the first week of the study. The hamper contains core ingredients to support adherence to the Sham diet, drawn from its key food groups. As with the MedDiet hamper, specific contents may vary seasonally but will remain consistent with the principles of the allocated study diet.
Control group
Placebo

Outcomes
Primary outcome [1] 344790 0
Difference in gastrointestinal symptom response between intervention and control group at week 8, measured by change in the Irritable Bowel Syndrome Symptom Severity Scale (IBS-SSS) with response defined as a change of 50 points or more from baseline.
Timepoint [1] 344790 0
Baseline, and Week 8 post-intervention commencement
Secondary outcome [1] 459218 0
Difference in changes to gastrointestinal symptoms between intervention and control group.
Timepoint [1] 459218 0
Baseline, Week 4 and Week 8 post-intervention commencement.
Secondary outcome [2] 459222 0
Difference in changes to depressive symptoms between intervention and control group.
Timepoint [2] 459222 0
Baseline, Week 4 and Week 8 post-intervention commencement.
Secondary outcome [3] 459223 0
Differences in changes to health-related quality of life between intervention and control group.
Timepoint [3] 459223 0
Baseline, Week 4 and Week 8 post-intervention commencement.
Secondary outcome [4] 463028 0
Differences in changes to anxiety symptoms between intervention and control group.
Timepoint [4] 463028 0
Baseline, Week 4 and Week 8 post-intervention commencement.
Secondary outcome [5] 463029 0
Difference in changes to stool frequency between intervention and control group
Timepoint [5] 463029 0
Baseline and Week 8 post-intervention commencement.
Secondary outcome [6] 463030 0
Difference in changes to stool consistency between intervention and control group
Timepoint [6] 463030 0
Baseline and Week 8 post-intervention commencement
Secondary outcome [7] 463031 0
Difference in changes to gastrointestinal symptoms (global) between intervention and control group
Timepoint [7] 463031 0
Baseline, Week 4 and Week 8 post-intervention commencement,
Secondary outcome [8] 463032 0
Differences in changes to gastrointestinal symptoms (reflux) between intervention and control group.
Timepoint [8] 463032 0
Baseline, Week 4 and Week 8 post-intervention commencement,
Secondary outcome [9] 463033 0
Differences in changes to gastrointestinal symptoms (abdominal pain) between intervention and control group.
Timepoint [9] 463033 0
Baseline, Week 4 and Week 8 post-intervention commencement.
Secondary outcome [10] 463034 0
Differences in changes to gastrointestinal symptoms (indigestion) between intervention and control group.
Timepoint [10] 463034 0
Baseline, Week 4 and Week 8 post-intervention commencement,
Secondary outcome [11] 463035 0
Differences in changes to gastrointestinal symptoms (diarrhoea) between intervention and control group.
Timepoint [11] 463035 0
Baseline, Week 4 and Week 8 post-intervention commencement
Secondary outcome [12] 463036 0
Differences in changes to gastrointestinal symptoms (constipation) between intervention and control group.
Timepoint [12] 463036 0
Baseline, Week 4 and Week 8 post-intervention commencement,
Secondary outcome [13] 463037 0
Differences in changes to gut microbiome composition between intervention and control group.
Timepoint [13] 463037 0
Baseline, Week 8 post-intervention commencement
Secondary outcome [14] 463038 0
Differences in changes to gut microbiome metabolites between intervention and control group.
Timepoint [14] 463038 0
Baseline, Week 8 post-intervention commencement.
Secondary outcome [15] 463039 0
Mediterranean Diet Adherence
Timepoint [15] 463039 0
Baseline, Week 8 post-intervention commencement
Secondary outcome [16] 463040 0
Dietary intake (composite measure)
Timepoint [16] 463040 0
Baseline, Week 8 post-intervention commencement

Eligibility
Key inclusion criteria
- Aged 18-65 years
- Irritable Bowel Syndrome (IBS) according to ROME V criteria of any IBS subtype (diarrhoea-predominant, constipation-predominant, mixed, unclassified) AND score 175 points or more on the IBS-Symptom Severity Score (IBS-SSS, indicating at least moderate symptoms)
- Mild-moderate symptoms of depression (scores of 5-14 on the PHQ-8) and/or mild-moderate symptoms of anxiety (scores of 5-14 on the GAD-7).
- Agree not to enrol in another interventional clinical research trial while in the study.
- Are English literate
- Have access to computer and internet.
Minimum age
18 Years
Maximum age
65 Years
Sex
Both males and females
Healthy volunteers
No
Key exclusion criteria
- Pregnant or breastfeeding.
- Known or suspected major medical conditions (e.g., insulin-dependent diabetes, cognitive disorders) which might impact study outcomes or participant’s ability to follow dietary intervention.
- Known or suspected gastrointestinal disorder (inflammatory bowel disease, coeliac disease, gastrointestinal cancer), or history of major gastrointestinal surgery (e.g., ileostomy, colostomy) likely to influence study outcomes.
- Serious psychiatric comorbidity (e.g. major depressive disorder, bipolar disorder, schizophrenia) which might impact participant safety, participant’s ability to follow dietary intervention or influence study outcomes.
- Co-existing eating disorder or score of 2 or more on the Screen for Disordered Eating, indicating increased risk for disordered eating.
- Body mass index (BMI) of or less than 20 kg/m2.
- Titrating dose of gastrointestinal or mental health medication in the last 4-weeks.
- Commencement of or change in psychological therapies (e.g., cognitive behaviour therapy) in the last 4-weeks.
- Commencement of new dietary treatment for IBS within the last 3-months
(e.g., low FODMAP, traditional dietary advice, gluten-free).
- Exposure to prebiotic or probiotic supplements in the last month, or antibiotics or bowel preparation for investigative procedures within the last 3-months.
- Dietary allergies/restrictions that would prevent dietary adherence (e.g., gluten free, vegan, sociocultural or religious reasons)

Study design
Purpose of the study
Treatment
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Participants will be randomised in a 1:1 allocation ratio. An external biostatistician will generate a randomisation table using random block sizes, which will be uploaded to REDCap to manage randomisation during the trial. Participants will be randomly allocated to their intervention arm after baseline data collection, prior to dietary counselling.
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
An external biostatistician will generate a randomisation table using random block sizes, which will be uploaded to REDCap to manage randomisation during the trial.
Masking / blinding
Blinded (masking used)
Who is / are masked / blinded?
The people receiving the treatment/s

The people assessing the outcomes
The people analysing the results/data
Intervention assignment
Parallel
Other design features
Phase
Not Applicable
Type of endpoint/s
Efficacy
Statistical methods / analysis

Recruitment
Recruitment status
Not yet recruiting
Date of first participant enrolment
Anticipated
29/06/2026
Actual
Date of last participant enrolment
Anticipated
31/12/2027
Actual
Date of last data collection
Anticipated
28/02/2028
Actual
Sample size
Target
100
Accrual to date
Final
Recruitment outside Australia
Country [1] 27952 0
New Zealand
State/province [1] 27952 0

Funding & Sponsors
Funding source category [1] 321414 0
Charities/Societies/Foundations
Name [1] 321414 0
Auckland Medical Research Foundation
Country [1] 321414 0
New Zealand
Primary sponsor type
University
Name
University of Auckland
Address
Country
New Zealand
Secondary sponsor category [1] 324208 0
None
Name [1] 324208 0
Address [1] 324208 0
Country [1] 324208 0

Ethics approval
Ethics application status
Approved
Ethics committee name [1] 319953 0
Northern B Health and Disability Ethics Committee 
Ethics committee address [1] 319953 0
Ethics committee country [1] 319953 0
New Zealand
Date submitted for ethics approval [1] 319953 0
13/03/2026
Approval date [1] 319953 0
13/04/2026
Ethics approval number [1] 319953 0

Summary
Brief summary
Trial website
Trial related presentations / publications
Public notes

Contacts
Principal investigator
Name 148942 0
Dr Nicola Gillies
Address 148942 0
University of Auckland, Facult of Medical and Health Sciences, 85 Park Road, Grafton, Auckland 1023
Country 148942 0
New Zealand
Phone 148942 0
+64 022 087 8065
Fax 148942 0
Email 148942 0
[email protected]
Contact person for public queries
Name 148943 0
Nicola Gillies
Address 148943 0
University of Auckland, Facult of Medical and Health Sciences, 85 Park Road, Grafton, Auckland 1023
Country 148943 0
New Zealand
Phone 148943 0
+64 022 087 8065
Fax 148943 0
Email 148943 0
[email protected]
Contact person for scientific queries
Name 148944 0
Nicola Gillies
Address 148944 0
University of Auckland, Facult of Medical and Health Sciences, 85 Park Road, Grafton, Auckland 1023
Country 148944 0
New Zealand
Phone 148944 0
+64 022 087 8065
Fax 148944 0
Email 148944 0
[email protected]

Data sharing statement
Will the study consider sharing individual participant data?
No


What supporting documents are/will be available?

No Supporting Document Provided


Results publications and other study-related documents

Documents added manually
No documents have been uploaded by study researchers.

Documents added automatically
No additional documents have been identified.