Dr Eirini Dimidi explains the background to the extensive project that resulted in the BDA evidence-based dietary guidelines for chronic constipation in adults.
The BDA has officially launched the first dietary guidelines for the management of chronic constipation, marking a significant shift in the advice dietitians and other healthcare professionals can offer to adults living with this common condition.1,2
Although constipation is often managed initially through dietary modifications, until now there have been no diet-specific, evidence-based guidelines to inform practice.
Existing national and international guidance on constipation management tended to focus mostly on pharmacological approaches and behavioural strategies, with only brief or generalised references to diet, typically “increase fibre” or “drink more water”.3
A defining feature of these BDA guidelines is their evidence-based approach.
They are the first dietary guidelines for chronic constipation to be developed entirely from evidence derived from randomised controlled trials.
In contrast to previous clinical guidelines, where dietary recommendations were not always based on strong evidence, these guidelines have been designed to ensure that advice offered to patients is both effective and safe, and supported by robust scientific evidence.3
This article describes the methodological framework underpinning the development of the BDA evidence-based dietary guidelines for chronic constipation and provides an overview of the key dietary recommendations arising from this work.
Why were these BDA guidelines needed?
Before this project, dietitians had to rely on fragmented evidence from individual trials, systematic reviews or clinical guidelines that had limited dietary recommendations.
While there was growing research exploring dietary supplements and specific foods for constipation, the quality, consistency and clinical applicability of findings varied widely.
In practice, this created uncertainty about which dietary interventions had robust evidence and inconsistency in dietetic care provided. The new guidelines filled that gap by providing:
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A transparent systematic synthesis of the evidence base
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Clear, outcome-specific recommendations
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Practical guidance on dietary management in adults with chronic idiopathic constipation.
Which patient population are the guidelines for?
The guidelines apply to adults with chronic idiopathic (primary) constipation – that is, constipation not explained by secondary causes, such as neurological disorders, pregnancy or medications.
How was this project initiated?
Recognising the need for clear, evidence-based guidance, the BDA General and Education Trust awarded us at King’s College London competitive funding to undertake a multi-year programme and develop comprehensive dietary guidelines for adults with chronic constipation.
A multidisciplinary Guidelines Steering Committee was subsequently established to oversee the project.
This included dietitians (Dr Eirini Dimidi, Professor Kevin Whelan and Dr Miranda Lomer), a nutrition scientist (Alice van der Schoot), a gastroenterologist (Dr Adam Farmer), a general practitioner (Dr Kevin Barrett) and a gut physiologist (Dr Mark Scott).
Bringing together expertise from across clinical disciplines ensured the guidelines were clinically relevant, methodologically robust and applicable to the range of healthcare professionals involved in the care of adults with chronic constipation.
How were the guidelines developed?
The guidelines adhered to internationally recognised standards for guideline development, including systematic review methodology, GRADE evidence appraisal, and Delphi consensus procedures.
The process of the development of the guidelines involved five key phases:
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Defining the scope of the dietary guidelines;
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Conducting four systematic reviews and meta-analyses;
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Developing initial dietary recommendation statements using the GRADE approach
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Conducting Delphi consensus surveys;
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Publishing and disseminating the new BDA guidelines
Phase 1: Defining the scope of the dietary guidelines
The Guideline Steering Committee first defined the scope of the guidelines using the Population, Intervention, Comparator, Outcome and Study design (PICOS) framework, which guided evidence searching, selection and appraisal.
The guidelines focused on dietary supplements, foods, drinks and whole-diet interventions for adults with chronic constipation who were otherwise healthy.
Key outcomes of interest were agreed a priori and included response to treatment, stool output (frequency and consistency), gastrointestinal symptoms, quality of life and adverse events.
Importantly, the committee decided to develop outcome-specific recommendations (e.g. magnesium oxide supplements soften stool consistency), rather than broad recommendations for constipation as a single entity (e.g. magnesium oxide supplements improve constipation).
This decision reflected the heterogeneous nature of chronic constipation and recognised that individual dietary interventions may differentially affect specific symptoms.
To ensure methodological rigour, only randomised controlled trials (RCTs) were eligible for informing the dietary recommendations, ensuring that the guidelines were grounded in the highest available level of evidence.
Phase 2: Conducting four systematic reviews and meta-analyses
In order to identify every single RCT that has ever been conducted on diet and chronic constipation, four comprehensive systematic reviews and meta-analyses were undertaken following the PRISMA and Cochrane guidelines.4,5
The systematic reviews were focused on:
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Fibre and prebiotic supplements
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Probiotic and synbiotic supplements
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Food supplements
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Foods, drinks and whole diets6-9
In total, 75 RCTs met the eligibility criteria and were subjected to meta-analyses to generate the pooled effect for the key constipation outcomes.
These were then used to develop the initial dietary recommendation statements.
Phase 3: Developing initial dietary recommendation statements using the GRADE approach
Initial dietary recommendation statements were drafted directly from the findings of the four systematic reviews and meta-analyses.
The evidence underpinning each statement was then appraised using the GRADE (Grading of Recommendations, Assessment, Development and Evaluation) framework, which was used to determine both the certainty of evidence (high, moderate, low or very low) and the strength of recommendation (strong or conditional).10
Overall, much of the evidence was rated as low or very low certainty, reflecting common methodological limitations across the available RCTs and underscoring the need for further high-quality trials in this area.
Importantly, however, almost half of the recommendation statements were classified as strong, where the balance of benefits versus harms was favourable, effect sizes were clinically meaningful, and interventions were considered acceptable, accessible and low -cost for patients.
Phase 4: Conducting Delphi consensus surveys
The draft recommendation statements subsequently underwent a multi-stage Delphi consensus process, during which all members of the Guideline Steering Committee reviewed the supporting evidence and independently voted on each statement.
A predefined threshold of ≥85% agreement was required for a recommendation to be accepted. Statements that did not reach consensus were revised in light of feedback and recirculated for additional Delphi rounds.
Ultimately, this process resulted in 59 evidence-based recommendation statements, which are summarised in Table 1 (below).
Phase 5: Publishing and disseminating the new BDA guidelines
The final guidelines were then written and included:
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59 dietary recommendation statements
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Good practice statements to provide guidance on how to apply recommendations in clinical practice
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A clinician-friendly table that summarises all statements (Table 1 below)
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12 research priorities to guide future work
Following a peer-review process, the guidelines were published open-access in two scientific journals: the Journal of Human Nutrition and Dietetics and Neurogastroenterology & Motility.1,2
The guidelines have also been widely covered and disseminated in the media, including the BBC, Telegraph, and NBC (Box 1), highlighting the huge interest of the public oin the dietary management of constipation.
The big question: what do the new BDA dietary guidelines recommend?
A clinician-friendly summary of all dietary recommendations is shown in Table 1 (click to enlarge).
In a clinical environment, dietitians may use this table to provide evidence-based advice for constipation, tailored to patient symptoms, preferences, tolerability and comorbidities.
In brief, the following dietary strategies are recommended for people living with chronic constipation, based on RCT evidence:
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Kiwifruits: 2–3 kiwifruits daily
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Prunes: 8–10 prunes daily
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Rye bread: 6–8 slices daily, although this may not be realistic for some patients.
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High mineral content water: 0.5–1.5L/d
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Psyllium supplements: at least 10g/d, starting at a low dose with gradual increments and accompanied by additional fluid intake
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Magnesium oxide supplements: 0.5–1.5g/d, starting at a low dose with gradual increments as tolerated
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Some, but not all, probiotic strains (e.g. Bifidobacterium lactis, Bacillus coagulans Unique IS2)
At the same time, senna supplements, synbiotic supplements and other probiotic strains (e.g. Lactobacillus casei Shirota) did not demonstrate any benefit and are therefore not recommended for the management of chronic constipation.
Similarly, there was insufficient RCT evidence to support the use of a high- fibre diet, where fibre is derived from a range of unspecified fibre-containing foods and drinks, in constipation.
Importantly, this does not suggest that fibre lacks health benefits in general. A high-fibre diet remains essential for overall gut health, and individuals should continue to aim to meet the UK national recommendation of 30g fibre per day.
What do we not know yet?
The guidelines highlighted several important gaps in the literature, providing a roadmap for future research on various dietary strategies, including various probiotics and synbiotic supplements, fermented foods, food products with inactivated bacteria, high-fibre foods and diets, additional fluids, vitamin C and potential trigger foods that worsen constipation.
Conclusion
The BDA evidence-based dietary guidelines for chronic constipation in adults translate a diverse research base into clear, actionable recommendations for practice.
For the first time, dietitians have a comprehensive, systematically developed resource identifying which foods, drinks and supplements can improve symptoms, while highlighting evidence gaps and reinforcing the central role of dietitians in evidence-based care.
Selected media coverage of BDA dietary guidelines for chronic constipation in the media
International Scientific Association for Probiotics and Prebiotics podcast
References
- Dimidi, E. et al. British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults. J Hum Nutr Diet 38, e70133, doi:10.1111/jhn.70133 (2025).
- Dimidi, E. et al. British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults. Neurogastroenterol Motil 37, e70173, doi:10.1111/nmo.70173 (2025).
- Dimidi, E. Dietary management of chronic constipation: a review of evidence-based strategies and clinical guidelines. Proc Nutr Soc 84, 398-410, doi:10.1017/S0029665125100694 (2025).
- Higgins JPT et al. Cochrane Handbook for Systematic Reviews of Interventions version 6.5 (updated August 2024). Cochrane, 2024. Available from www.cochrane.org/handbook
- Page, M. J. et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ 372, n71, doi:10.1136/bmj.n71 (2021).
- van der Schoot, A., Creedon, A., Whelan, K. & Dimidi, E. The effect of food, vitamin, or mineral supplements on chronic constipation in adults: A systematic review and meta-analysis of randomized controlled trials. Neurogastroenterol Motil 35, e14613, doi:10.1111/nmo.14613 (2023).
- van der Schoot, A., Drysdale, C., Whelan, K. & Dimidi, E. The Effect of Fiber Supplementation on Chronic Constipation in Adults: An Updated Systematic Review and Meta-Analysis of Randomized Controlled Trials. Am J Clin Nutr 116, 953-969, doi:10.1093/ajcn/nqac184 (2022).
- van der Schoot, A., Helander, C., Whelan, K. & Dimidi, E. Probiotics and synbiotics in chronic constipation in adults: A systematic review and meta-analysis of randomized controlled trials. Clin Nutr 41, 2759-2777, doi:10.1016/j.clnu.2022.10.015 (2022).
- van der Schoot, A., Katsirma, Z., Whelan, K. & Dimidi, E. Systematic review and meta-analysis: Foods, drinks and diets and their effect on chronic constipation in adults. Aliment Pharmacol Ther 59, 157-174, doi:10.1111/apt.17782 (2024).
- Schünemann H, Brożek J, Guyatt G & Oxman A. GRADE Handbook, <https://gdt.gradepro.org/app/handbook/handbook.html> (2013).
