Gut health: Evidence-Based Supplement Guide

Six of the 72 people in Avelor with a saved stack hold something taken for gut health. This category has the widest gap between the confidence of its marketing and the certainty of its evidence, and the gap is measurable rather than a matter of opinion. The reviews below repeatedly grade their own findings as low or very low certainty while reporting a positive effect, and the labels carry the effect without the grade. Start with the idea the category is built on. A review of intestinal barrier function concluded that it is **still unproven** that restoring barrier function improves clinical outcomes in disease (PMID 31076401). The same review notes that barrier dysfunction is real and worth clinicians' attention. A narrative review covers the relationship between the microbiota, permeability and systemic inflammation (PMID 37505311). Glutamine, the compound most often sold for this, has promising experimental-model data and a review concluding that further studies are needed before it can be evaluated in clinical practice (PMID 27749689). So "leaky gut" names a real measurable phenomenon and does not yet name a treatable target, and a product sold to fix it is ahead of the evidence. Probiotics have more evidence and a more awkward reading. A systematic review and meta-analysis reported that some combinations or strains may benefit irritable bowel syndrome, and that certainty by GRADE criteria was **low to very low across almost all analyses** (PMID 37541528). A network meta-analysis found Bifidobacterium and Lactobacillus dominant among effective strains while concluding the most effective combination remains unclear, and found prebiotics and synbiotics showed no significant improvement (PMID 38999862). A further network meta-analysis reached compatible conclusions (PMID 35433498). Crucially, a systematic review and meta-analysis found efficacy is both **strain-specific and disease-specific** (PMID 29868585), which two practical reviews translate into how to choose a product (PMID 30586435, 38542689). That is why "probiotics work" is not a usable sentence: the evidence attaches to particular strains for particular conditions. What has better evidence is dietary and unglamorous. A network meta-analysis ranked a low FODMAP diet first for every endpoint studied in irritable bowel syndrome (PMID 34376515). It noted the trials were mostly in specialist care and did not study reintroduction or personalisation. Two further reviews agree that it carries the most evidence among dietary interventions (PMID 33585949, 40258374). Fibre has a meta-analysis in chronic constipation (PMID 35816465) and a network meta-analysis placing soluble fibre alongside antispasmodics and neuromodulators in irritable bowel syndrome (PMID 31859183). A review of over-the-counter options rated the evidence for fibre as moderate and placed other agents first-line (PMID 33767108). Peppermint oil was found superior to placebo with **more frequent adverse events and very low quality evidence** (PMID 35942669). An earlier review was more favourable (PMID 24100754). One randomised trial of a targeted-release formulation concluded against further development despite reducing pain (PMID 31470006). A clinical guideline covers all of this formally (PMID 33315591, 39598092).

1. **Get a diagnosis before buying a product.** Irritable bowel syndrome, coeliac disease and inflammatory bowel disease are different conditions and the guideline exists for sorting them (PMID 33315591). 2. **Try the dietary route first.** It has the most evidence of anything in this guide (PMID 34376515, 40258374). 3. **Do a low FODMAP diet with a dietitian, not from an app.** The trials did not test reintroduction or personalisation, which is the part that makes it liveable (PMID 34376515). 4. **If you buy a probiotic, buy a strain studied for your condition**, not a product labelled "probiotic" (PMID 29868585, 30586435). 5. **Treat low-certainty findings as low-certainty.** Almost every positive result here is graded low or very low by its own review (PMID 37541528, 35942669).

Where the research supports a timeframe, the irritable bowel trials pooled in the network meta-analysis mostly ran **four to twelve weeks** (PMID 31859183). That review states the long-term relative efficacy of these treatments is therefore unknown. The low FODMAP trials are of similar length and did not follow reintroduction (PMID 34376515). No duration is offered for barrier or permeability products, because no clinical outcome has been established for them to act on (PMID 31076401).

- **Almost every positive finding here is graded low or very low certainty by the review reporting it** (PMID 37541528, 35942669). A label reporting the effect without the grade is not lying and is not telling you the thing that matters. - **Probiotic evidence does not transfer across strains or conditions** (PMID 29868585). A trial in antibiotic-associated diarrhoea says nothing about bloating. - **"Leaky gut" is a real measurement without an established treatment** (PMID 31076401). This guide does not say the phenomenon is imaginary, and it does not say a product fixes it. - **Glutamine's supporting data is largely from experimental models** (PMID 27749689). - **The low FODMAP trials were mostly in specialist care** (PMID 34376515), so the results describe supported patients rather than someone following a list found online. - **Peppermint oil's own meta-analysis reports more adverse events alongside the benefit** (PMID 35942669), and a targeted-release trial concluded against further development (PMID 31470006).

- **Probiotics are live organisms and are not risk-free for everyone.** Serious adverse events have been reported in severely debilitated or immunocompromised patients, including those with central venous catheters (PMID 31039287). If you are immunocompromised, have a central line, or are seriously unwell, do not start one without asking **your clinician**. - **Rectal bleeding, unexplained weight loss, a persistent change in bowel habit, anaemia, or difficulty swallowing are reasons to see a doctor**, not reasons to try a gut supplement. Early-onset colorectal cancer is rising and has recognised warning signs (PMID 33417940). - **New or changed symptoms after starting an antibiotic deserve a clinician's view** rather than a probiotic chosen at random, since the evidence is strain-specific and the setting matters (PMID 31039287, 35794520). - **Chronic constipation has a first-line pathway that is not a supplement** (PMID 33767108, 29239347). Raise it with **a clinician or pharmacist** before layering products. - **Fibre and soluble-gel products can change how other oral medicines are absorbed.** If you take a regular medicine, raise timing with **a pharmacist** (PMID 31859183).

Resolving to an entity and being interaction-checkable are different things. The interaction catalogue keys on a collapsed name string rather than an entity id. Resolves **and** has a catalogue key, so it can be interaction-checked: - `avelor:sup:glutamine` Resolves but has **no catalogue key**, so it displays as recognised and is checked against nothing: - `avelor:sup:probiotics` - `avelor:sup:psyllium-husk` - `avelor:sup:slippery-elm` No supplement entity, and none is invented here: **peppermint oil**, **Saccharomyces boulardii**, **Lactobacillus**, **Bifidobacterium**, **prebiotics**, **inulin** and **digestive enzymes**. The probiotic case is the sharpest argument in these guides for why a single entity is not enough. The evidence is strain-specific and disease-specific, proven so by its own meta-analysis, and the registry holds exactly one entity called `probiotics` which carries no catalogue key. So the product models as one undifferentiated thing the category whose central finding is that it is not one thing, and then checks that thing against nothing. `avelor:sup:glutamine` is the only fully checkable entity in this guide, and it is the compound whose own review says clinical evaluation has not yet been done.

| PMID | Title | | --- | --- | | 31076401 | "Leaky gut: mechanisms, measurement and clinical implications in humans" | | 37505311 | "Gut microbiota, intestinal permeability, and systemic inflammation: a narrative review" | | 27749689 | "Glutamine and the regulation of intestinal permeability: from bench to bedside" | | 37541528 | "Efficacy of Probiotics in Irritable Bowel Syndrome: Systematic Review and Meta-analysis" | | 38999862 | "The Efficacy of Probiotics, Prebiotics, Synbiotics, and Fecal Microbiota Transplantation in Irritable Bowel Syndrome: A Systematic Review and Network Meta-Analysis" | | 35433498 | "Efficacy of Probiotics for Irritable Bowel Syndrome: A Systematic Review and Network Meta-Analysis" | | 29868585 | "Strain-Specificity and Disease-Specificity of Probiotic Efficacy: A Systematic Review and Meta-Analysis" | | 30586435 | "Choosing an appropriate probiotic product for your patient: An evidence-based practical guide" | | 38542689 | "Prebiotics and Probiotics for Gastrointestinal Disorders" | | 34376515 | "Efficacy of a low FODMAP diet in irritable bowel syndrome: systematic review and network meta-analysis" | | 33585949 | "Efficacy of a low-FODMAP diet in adult irritable bowel syndrome: a systematic review and meta-analysis" | | 40258374 | "Efficacy of dietary interventions in irritable bowel syndrome: a systematic review and network meta-analysis" | | 35816465 | "The Effect of Fiber Supplementation on Chronic Constipation in Adults: An Updated Systematic Review and Meta-Analysis of Randomized Controlled Trials" | | 31859183 | "Efficacy of soluble fibre, antispasmodic drugs, and gut-brain neuromodulators in irritable bowel syndrome: a systematic review and network meta-analysis" | | 33767108 | "Efficacy and Safety of Over-the-Counter Therapies for Chronic Constipation: An Updated Systematic Review" | | 35942669 | "Systematic review and meta-analysis: efficacy of peppermint oil in irritable bowel syndrome" | | 24100754 | "Peppermint oil for the treatment of irritable bowel syndrome: a systematic review and meta-analysis" | | 31470006 | "Efficacy and Safety of Peppermint Oil in a Randomized, Double-Blind Trial of Patients With Irritable Bowel Syndrome" | | 33315591 | "ACG Clinical Guideline: Management of Irritable Bowel Syndrome" | | 39598092 | "A Review of Pharmacologic and Non-Pharmacologic Therapies in the Management of Irritable Bowel Syndrome: Current Recommendations and Evidence" | | 31039287 | "Probiotics for the prevention of pediatric antibiotic-associated diarrhea" | | 35794520 | "Early use of probiotics might prevent antibiotic-associated diarrhea in elderly (>65 years): a systematic review and meta-analysis" | | 29239347 | "Chronic constipation" | | 33417940 | "An Update on the Epidemiology, Molecular Characterization, Diagnosis, and Screening Strategies for Early-Onset Colorectal Cancer" |