Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterised by chronic abdominal discomfort, bloating, and altered bowel habits. Affecting approximately 10–15% of the global population, IBS presents significant challenges for both patients and healthcare providers due to its multifactorial aetiology and the absence of a definitive cure. Dietary strategies have emerged as pivotal tools in managing symptoms, with the Low-FODMAP and gluten-free diets gaining considerable attention. This article explores the scientific evidence behind these approaches and evaluates the potential benefits of combining them.
Understanding the Low-FODMAP Diet
The Low-FODMAP diet, developed by researchers at Monash University, targets fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. These short-chain carbohydrates are poorly absorbed in the gastrointestinal tract, leading to increased water content and fermentation in the colon, which exacerbate IBS symptoms. Clinical studies have consistently demonstrated the efficacy of the Low-FODMAP diet in reducing symptoms for up to 75% of IBS patients.
Mechanism of Action
FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols) exert their effects through two primary mechanisms: osmotic effects and fermentation by gut microbiota[1]
Osmotic Effects
Upon ingestion, FODMAPs are poorly absorbed in the small intestine, leading to an increase in osmotic pressure1. This increased osmotic pressure draws water into the intestinal lumen, resulting in luminal distension. The distension of the intestinal wall activates stretch receptors, which can stimulate the release of hormones and neurotransmitters that contribute to the development of IBS symptoms[2].
Fermentation by Gut Microbiota
Undigested FODMAPs are fermented by the gut microbiota in the colon, producing short-chain fatty acids (SCFAs) and gas. The production of gas, particularly nitrogen, oxygen, carbon dioxide, and hydrogen, contributes to luminal distension and bloating. The SCFAs produced during fermentation can also stimulate the release of hormones and neurotransmitters, exacerbating IBS symptoms[3].
Symptom Relief through FODMAP Restriction
By limiting dietary intake of FODMAPs, patients experience reduced luminal distension and symptom relief. The reduction in FODMAP intake decreases the amount of undigested carbohydrates available for fermentation, leading to a decrease in gas production and luminal distension. This decrease in luminal distension and gas production reduces the stimulation of stretch receptors and the release of hormones and neurotransmitters, ultimately leading to symptom relief.
In summary, the mechanism of action of FODMAPs involves both osmotic effects and fermentation by gut microbiota, leading to luminal distension and gas production, which are key drivers of IBS symptoms. By restricting dietary FODMAP intake, patients can experience reduced luminal distension and symptom relief.
Evidence-Based Benefits
An observational study published in the “Journal of Human Nutrition and Diet” (2025) highlighted that the Low-FODMAP diet significantly improves abdominal pain, bloating, and diarrhoea in IBS patients. However, concerns about its restrictive nature and potential nutritional deficiencies underline the need for professional guidance[4]. https://link.springer.com/article/10.1007/s10620-024-08671-8
The Role of Gluten-Free Diets in IBS
Although traditionally associated with coeliac disease, gluten-free diets (GFDs) have gained traction among IBS patients. Non-coeliac gluten sensitivity (NCGS) is increasingly recognised as a condition wherein individuals experience gastrointestinal and extraintestinal symptoms following gluten consumption, despite testing negative for coeliac disease and wheat allergy.
Effectiveness of GFDs in IBS Patients
Several studies have demonstrated the effectiveness of GFDs in improving symptoms in IBS patients with NCGS[5]. A study found that a low FODMAP GFD led to significant improvements in clinical and psychological symptoms in NCGS patients[6]. Another study found that a GFD reduced symptoms of abdominal pain, bloating, and tiredness in IBS patients[7].
The Wheat Conundrum
It is important to note that wheat, a common source of gluten, also contains fructans—a high-FODMAP carbohydrate. Consequently, the symptom improvement seen with gluten-free diets may, in some cases, result from reduced FODMAP intake rather than gluten exclusion per se. This interplay complicates the differentiation between gluten and FODMAP triggers.
Combining Low-FODMAP and Gluten-Free Approaches
Given the overlapping mechanisms and dietary components of Low-FODMAP and gluten-free diets, combining these approaches may provide synergistic benefits for IBS patients. However, this dual approach requires careful implementation to avoid excessive dietary restriction and ensure nutritional adequacy.
Scientific Evidence for Combined Approaches
A pilot study published in “Clinical Gastroenterology and Hepatology” (2021) examined IBS patients who followed a combined Low-FODMAP and gluten-free diet. The results indicated significant improvements in symptom severity and quality of life compared to those who followed either diet alone. While promising, larger-scale studies are needed to confirm these findings and establish standardised protocols. A recent paper in the Journal Digestive Diseases and Science followed this pilot with a larger study[8].
Summary of Results
The study analysed the effects of a Low-Fermentable Gluten-Free Diet (LF-GFD) on patients with Irritable Bowel Syndrome (IBS). The results showed that LF-GFD significantly improved symptoms, quality of life, and reduced anxiety and depression in IBS patients.
Key Findings:
- LF-GFD reduced bloating ratings by 58% and pain scores by 42%.
- LF-GFD improved IBS Symptom Severity Scale (IBS-SSS) scores by 1.42 points and IBS Quality of Life (IBS-QoL) ratings by 3.75 points.
- LF-GFD decreased Self-Rating Depression Scale (SDS) scores by 2.56 points and Self-Rating Anxiety Scale (SAS) scores by 4.30 points.
Conclusion:
LF-GFD therapy is effective in enhancing clinical symptoms and reducing anxiety and depression in individuals diagnosed with IBS.
Practical Considerations
For clinicians, recommending a combined dietary approach involves:
- Thorough Assessment: Identifying specific dietary triggers through patient history, symptom diaries, and elimination-reintroduction protocols.
- Patient Education: Empowering patients to understand food labels and plan balanced meals to avoid deficiencies.
- Multidisciplinary Support: Collaboration with qualified nutritional professionals to ensure sustainable adherence and address psychosocial aspects of dietary changes.
Addressing Common Challenges
Restrictive Nature of Combined Diets
The dual restrictions of a Low-FODMAP and gluten-free diet can be daunting for patients. Social and cultural factors, as well as the potential for disordered eating behaviours, should be carefully managed. Clinicians must emphasise gradual changes and realistic goals.
Nutritional Adequacy
Patients on combined diets may face risks of inadequate fibre, calcium, and B-vitamin intake. Encouraging the inclusion of Low-FODMAP, gluten-free sources of nutrients—such as quinoa, spinach, and lactose-free dairy—can mitigate these risks.
Role of Gut Microbiota
The impact of these diets on gut microbiota is an evolving area of research. While the Low-FODMAP diet can reduce symptom-driving bacteria, prolonged restriction may negatively affect beneficial microbes. Periodic reintroduction of FODMAPs under professional guidance helps maintain microbial diversity.
Practical Tips for Clinicians
- Start with Monotherapy: Initiate either Low-FODMAP or gluten-free protocols based on the patient’s dominant symptoms and dietary history. Assess response before considering combination strategies.
- Personalise the Approach: Recognise that IBS triggers vary among individuals. A tailored plan that reflects the patient’s unique needs and preferences ensures better outcomes.
- Leverage Technology: Recommend apps like Monash University’s FODMAP app to support meal planning and symptom tracking.
- Monitor Progress: Regular follow-ups allow for adjustments, reintroductions, and addressing emerging challenges.
Conclusion
IBS management requires a nuanced approach that balances symptom control with quality of life. The Low-FODMAP and gluten-free diets have demonstrated efficacy in alleviating IBS symptoms, and emerging evidence suggests that their combination may benefit select patients. However, this approach should be guided by a comprehensive evaluation, professional support, and ongoing monitoring to avoid pitfalls associated with excessive restriction. As the field of personalised nutrition evolves, integrating dietary interventions with insights from gut microbiome research holds promise for enhancing IBS care.
A simplified, less restrictive low FODMAP diet may be a viable option for managing irritable bowel syndrome (IBS) symptoms, according to a double-blind, pilot randomised controlled trial[9]. The study compared the efficacy of a traditional low FODMAP diet restriction phase with a more targeted or simplified restriction phase, which only eliminated fructans and galacto-oligosaccharides. The results suggest that a simplified approach may be just as effective in reducing IBS symptoms as the traditional method.
By equipping patients with evidence-based strategies and empathetic support, healthcare providers can empower individuals to navigate the complexities of IBS with confidence and improved well-being.
References
[1] Gibson, P. R. & Shepherd, S. J. (2010). Evidence-based dietary management of functional gastrointestinal symptoms: the fodmap approach.. Journal Of Gastroenterology And Hepatology.
[2] Grez, C., Vega, Á., & Araya, M. (2019). [fermentable oligosaccharides, disaccharides, monosaccharides and polyols (fodmaps)].. Revista Medica De Chile
[3] Ochoa, K. C., Samant, S., Liu, A., Duysburgh, C., Marzorati, M., Singh, P., Hachuel, D., & Wallach, T. (2022). In-vitro efficacy of targeted fodmap enzymatic digestion in a high-fidelity simulated gastrointestinal environment. BioRxiv.
[4] Foulkes R, Shah P, Twomey A, Dami L, Jones D, Lomer MCE. A service evaluation of FODMAP restriction, FODMAP reintroduction and long-term follow-up in the dietary management of irritable bowel syndrome. J Hum Nutr Diet. 2025 Feb;38(1):e13393. doi: 10.1111/jhn.13393. Epub 2024 Nov 5. PMID: 39498596; PMCID: PMC11589392.
[5] Zanwar VG, Pawar SV, Gambhire PA, Jain SS, Surude RG, Shah VB, Contractor QQ, Rathi PM. Symptomatic improvement with gluten restriction in irritable bowel syndrome: a prospective, randomized, double blinded placebo controlled trial. Intest Res. 2016 Oct;14(4):343-350. doi: 10.5217/ir.2016.14.4.343. Epub 2016 Oct 17.
[6] Dieterich W, Schuppan D, Schink M, Schwappacher R, Wirtz S, Agaimy A, Neurath MF, Zopf Y. Influence of low FODMAP and gluten-free diets on disease activity and intestinal microbiota in patients with non-celiac gluten sensitivity. Clin Nutr. 2019 Apr;38(2):697-707.
[7] Zanwar VG, Pawar SV, Gambhire PA, Jain SS, Surude RG, Shah VB, Contractor QQ, Rathi PM. Symptomatic improvement with gluten restriction in irritable bowel syndrome: a prospective, randomized, double blinded placebo controlled trial. Intest Res. 2016 Oct;14(4):343-350.
[8] Zhang J, Yu P, Xu Y, Lu XY, Xu Y, Hang J, Zhang Y. Efficacy and Safety of a Low-FODMAP Diet in Combination with a Gluten-Free Diet for Adult Irritable Bowel Syndrome: A Systematic Review and Meta-Analysis. Dig Dis Sci. 2024 Nov;69(11):4124-4132.
[9] Singh P, Chey SW, Nee J, Eswaran S; Dietary Therapy in IBS Working Group; Lembo A, Chey WD. Is a Simplified, Less Restrictive Low FODMAP Diet Possible? Results from a Double-Blind, Pilot Randomized Controlled Trial. Clin Gastroenterol Hepatol. 2024 May 9:S1542-3565(24)00428-2.
