Research & Clinical Studies
The peer-reviewed studies and clinical trials that underpin the content on IBS.ie. Each article on this site is referenced against published research — primarily PubMed-indexed trials. This page gives direct access to the source material, with AI-assisted summaries for deeper exploration.
A Diet Low in FODMAPs Reduces Symptoms of Irritable Bowel Syndrome
A landmark randomised controlled crossover trial establishing the low-FODMAP diet as a clinically meaningful intervention for IBS. Thirty IBS patients followed both a low-FODMAP diet and a typical Australian diet for 21 days each. The low-FODMAP diet produced significantly greater symptom reduction across all IBS subtypes compared to the control diet.
Randomized Clinical Trial: Efficacy of Lactobacillus acidophilus DDS-1 in Irritable Bowel Syndrome
A randomised double-blind placebo-controlled trial across 12 gastroenterology clinics. L. acidophilus DDS-1 supplementation produced a 52.3% significant responder rate versus placebo (P < 0.001) on abdominal pain severity. IBS Symptom Severity Scale scores also improved significantly. One of the more methodologically robust probiotic trials in the IBS literature.
Peppermint Oil for the Treatment of Irritable Bowel Syndrome: A Systematic Review and Meta-Analysis
Systematic review and meta-analysis of randomised controlled trials on peppermint oil in IBS. Enteric-coated peppermint oil was significantly more effective than placebo for global IBS symptoms and abdominal pain. Peppermint oil was nearly twice as likely as placebo to produce a positive response. Established enteric coating as the critical formulation requirement.
Systematic Review: The Efficacy of Herbal Therapies in Irritable Bowel Syndrome
A Cochrane-methodology systematic review evaluating herbal therapies for IBS. Peppermint oil was the only herbal treatment with sufficient quality evidence to support a firm conclusion, and was found significantly superior to placebo for global IBS symptom relief. This review underpinned international guidelines acknowledging enteric-coated peppermint oil as a valid first-line natural option for IBS symptom management.
Fermented Milk Containing Lactobacillus bulgaricus and Streptococcus thermophilus in IBS-D
RCT examining fermented milk containing L. bulgaricus, S. thermophilus and L. acidophilus in IBS-D patients. Intestinal permeability — a key marker of gut barrier dysfunction — decreased significantly in the treatment group (P = 0.004) versus placebo. Clinical symptom scores improved. Provided clinical evidence for the three strains found in authentic Greek yogurt culture.
Lactobacillus delbrueckii subsp. bulgaricus 2038 and Streptococcus thermophilus 1131 Ameliorate Barrier Dysfunction in Human Intestinal Models
A 2025 study using human iPSC-derived intestinal models to demonstrate that L. bulgaricus 2038 and S. thermophilus 1131 protect and restore intestinal epithelial barrier function. Provides updated mechanistic evidence for how the Greek yogurt strains protect the gut lining — directly relevant to IBS where increased intestinal permeability is a documented feature, particularly in IBS-D.
Kefir Consumption and Health Effects Based on Human Clinical Trials: An Overview
A 2025 systematic overview of human clinical trials on kefir consumption and health outcomes. Reviews the evidence across gut health, microbiome composition, lactose tolerance and IBS-related outcomes. Provides an up-to-date synthesis of the clinical evidence base for kefir, consolidating findings across multiple trials including effects on bowel function, gut microbiota and digestive symptoms.
The Microbiota and Health Promoting Characteristics of the Fermented Beverage Kefir
Comprehensive review of kefir's microbiological composition and health effects. Documents kefir's 30–50 probiotic species diversity, reviews the evidence for microbiome modulation, and examines gut transit time effects. Foundational reference for the mechanisms behind kefir's gut health benefits.
A Meta-Analysis of the Clinical Use of Curcumin for Irritable Bowel Syndrome
Meta-analysis of randomised trials on curcumin supplementation in IBS. Overall positive effect on IBS symptom severity, particularly abdominal pain and quality of life scores. Highlights the significant bioavailability challenge — curcumin absorption is poor without enhancers. Confirms black pepper (piperine) and fat as the critical co-factors for therapeutic effect.
Influence of Piperine on the Pharmacokinetics of Curcumin in Animals and Human Volunteers
The foundational study demonstrating that piperine (the active compound in black pepper) increases curcumin bioavailability by up to 2,000% in humans. Established the scientific basis for combining turmeric with black pepper — one of the most cited findings in nutritional supplement research and directly relevant to the clinical use of turmeric for IBS.
Evidence-Based Dietary Management of Functional Gastrointestinal Symptoms: The FODMAP Approach
Foundational paper from the Monash University researchers who developed the FODMAP concept. Outlines the evidence base for dietary restriction of fermentable carbohydrates in IBS and other functional gut disorders. Established the theoretical and clinical framework that underpins the low-FODMAP diet now used globally.
Fructan Rather Than Gluten Elicits Symptoms in Patients with Self-Reported Non-Celiac Gluten Sensitivity
Double-blind crossover trial demonstrating that fructans — not gluten — are responsible for symptoms in most people who believe they have non-coeliac gluten sensitivity. Directly relevant to IBS as it explains why wheat triggers symptoms without requiring coeliac disease, and why the low-FODMAP approach (which reduces fructans) works for people who had attributed their symptoms to gluten.
Gut-Brain Axis and the Microbiota
Comprehensive review of the gut-brain axis — the two-way communication system between the central nervous system and the enteric nervous system. Documents the role of the microbiome as a key participant in this axis, and the mechanisms by which gut bacteria influence brain function and vice versa. Foundational reference for understanding why stress worsens IBS and why psychological interventions have clinical benefit.
Serotonin Signalling in the Gut — Functions, Dysfunctions and Therapeutic Targets
Authoritative review establishing that 95% of the body's serotonin is produced in the gut, and documenting how dysregulated serotonin signalling underlies altered motility in both IBS-C and IBS-D. Explains why IBS-D involves excess serotonin release and IBS-C involves reduced signalling — and the rationale for serotonin-targeting medications in IBS management.
A Novel Delivery System of Peppermint Oil is an Effective Therapy for Irritable Bowel Syndrome Symptoms
RCT demonstrating that a pH-dependent, site-specific delivery system for peppermint oil significantly reduced IBS symptom severity compared to placebo. Reinforced the critical importance of enteric coating — peppermint oil must survive stomach transit intact to reach the small intestine where it exerts its antispasmodic effect on smooth muscle.
Kefir Improves Lactose Digestion and Tolerance in Adults with Lactose Malabsorption
Clinical study demonstrating that people with lactose malabsorption tolerate kefir significantly better than regular milk, attributing this to continued lactase activity from the live bacteria post-consumption. Directly relevant to IBS patients with overlapping lactose sensitivity who want to consume fermented dairy for its probiotic benefits.
Sex Hormones in the Modulation of Irritable Bowel Syndrome
Comprehensive review of how sex hormones modulate IBS at multiple levels of the brain-gut-microbiota axis. Documents the role of oestrogen and progesterone in visceral sensitivity, gut motility, intestinal permeability and immune activation of the intestinal mucosa. Explains the female predominance in IBS and the correlation between IBS symptoms and hormonal status across the menstrual cycle, pregnancy and menopause. Introduces the concept of the "microgenderome" — the interaction between host sex and commensal microbiota.
Update on Irritable Bowel Syndrome and Gender Differences
Review synthesising the evidence on sex and gender differences in IBS prevalence, symptom presentation, psychological comorbidities and treatment response. Documents that women with IBS report more severe pain, greater bloating, and stronger menstrual cycle-related symptom fluctuation than men. Covers the biological mechanisms — serotonin pathway differences, autonomic nervous system reactivity — that underlie these clinical differences.
Nonsteroidal Anti-Inflammatory Drugs for Dysmenorrhoea
Cochrane systematic review of randomised controlled trials on NSAIDs for primary dysmenorrhoea. Establishes that prostaglandins — hormone-like compounds that drive uterine contractions — are also responsible for increased gut motility and secretion in the premenstrual phase. Provides the mechanistic foundation for the well-documented worsening of IBS-D symptoms before and during menstruation in women.
Gender Differences in Patient-Reported Outcomes for Irritable Bowel Syndrome
Large observational study examining gender differences in IBS symptom burden, quality of life, healthcare utilisation and treatment response. Men with IBS reported lower pain scores and were significantly less likely to seek medical help despite comparable symptom severity to women. Documents the underdiagnosis gap in male IBS and the tendency for men to have IBS-D rather than IBS-C. Provides the clinical evidence base for the assertion that IBS in men is substantially underreported.
Gut Microbiome Influences Efficacy of PD-1-Based Immunotherapy Against Epithelial Tumors
Landmark study establishing that Akkermansia muciniphila abundance in the gut microbiome is a key differentiator between patients who respond to anti-PD-1 immunotherapy and those who do not. Non-responding patients had significantly lower Akkermansia levels. Oral supplementation with Akkermansia restored immunotherapy response in antibiotic-treated mice. Identified gut microbiome health as a measurable factor in cancer treatment outcomes.
Intestinal Akkermansia Muciniphila Predicts Clinical Response to PD-1 Blockade in Patients with Advanced Non-Small-Cell Lung Cancer
Human clinical study demonstrating that baseline Akkermansia muciniphila levels predict immunotherapy response more accurately than PD-L1 expression — the standard clinical biomarker. Akkermansia-positive patients achieved a 28% objective response rate versus 18% in Akkermansia-negative patients. Provides the strongest human evidence to date for Akkermansia as a clinically actionable biomarker in oncology.
A Purified Membrane Protein from Akkermansia Muciniphila or the Pasteurized Bacterium Improves Metabolism in Obese and Diabetic Mice
Identified Amuc_1100 as the specific outer membrane protein responsible for many of Akkermansia's metabolic benefits, and demonstrated that pasteurised Akkermansia produces equal or superior metabolic results to the live bacterium. Foundational paper for the development of pasteurised Akkermansia supplements and the postbiotic concept for next-generation probiotics.
Supplementation with Akkermansia Muciniphila in Overweight and Obese Human Volunteers: A Proof-of-Concept Exploratory Study
First human clinical trial of Akkermansia muciniphila supplementation. Insulin-resistant adults supplemented with live or pasteurised Akkermansia for three months showed significant improvements in insulin sensitivity, fasting glucose, blood cholesterol and liver enzyme markers. Pasteurised Akkermansia produced results equal to or greater than the live form. Well-tolerated safety profile supported the EU Novel Food application approved in 2021.
Akkermansia Muciniphila gen. nov., sp. nov., a Human Intestinal Mucin-Degrading Bacterium
The original paper describing the discovery and characterisation of Akkermansia muciniphila as a new bacterial species. Established its identity as a mucin-degrading anaerobe resident in the human intestinal tract and laid the foundation for two decades of subsequent research into its role in gut health, metabolic disease and immunity.
