Gut Barrier and Mucosa

1. What This Mechanism of Action Is

The intestinal barrier consists of a mucus layer, epithelial cells, and tight junctions. It regulates the passage of nutrients, water, and immune mediators while blocking pathogens and toxins. A compromised barrier ('leaky gut') may promote inflammation and is associated with chronic diseases. Mechanistically, substances may act on mucus production, the expression of tight-junction proteins (e.g., occludin, claudin), or the composition of the microbiome.

In humans, the intestinal barrier can be measured indirectly via biomarkers such as zonulin, LPS, or LBP in the blood. Direct methods (e.g., lactulose-mannitol test) are labour-intensive and rarely used in studies. While animal experiments and cell models allow for detailed mechanistic studies, they are not always translatable to humans. Controlled human studies are therefore critical but are often small and heterogeneous.

2. Which Substances Target This Mechanism

All substances in the database for which this mechanism of action is described—ranked by the extent of human testing. The numbers represent studies per type of investigation.

3. How Robust This Evidence Is

The most robust evidence exists for the gut microbiome (97 controlled studies) and probiotics (21 controlled studies), followed by zinc (4 controlled studies) and turmeric/curcumin (3 controlled studies). Substances such as vitamin D, omega-3 fatty acids, or beta-glucans show indications from observational studies or small interventional studies. Humic acid complexes, frankincense, or black cumin have so far only been investigated in cell or animal models, but not in humans.

Many substances act through similar mechanisms: they modulate inflammatory processes (e.g., the NF-κB signalling pathway), strengthen tight junctions, or promote a healthy microbiome. While extrapolation of laboratory findings to humans is plausible, it is not confirmed. For example, humic acid complexes show stabilisation of the gut barrier in animal studies, but clinical data are lacking. A similar situation applies to sulforaphane or resveratrol, which show promise in cell models.

4. Key Human Studies

• 1 Endotoxins and Non-Alcoholic Fatty Liver Disease (2021) — Gut microbiome
• 2 Probiotic Formulation for Patients With Bipolar or Schizophrenia Spectrum Disorder: A Double-Blind, Randomised Placebo-Controlled Trial (2025) — Gut microbiome
• 3 Effect of a Multistrain Probiotic on Leaky Gut in Patients with Diarrhoea-Predominant Irritable Bowel Syndrome: A Pilot Study (2023) — Gut microbiome
• 4 Effect of Probiotic Supplementation on Intestinal Permeability in Overweight and Obesity: A Systematic Review of Randomised Controlled Trials and Animal Studies (2024) — Probiotics
• 5 Effect of probiotic supplementation on migraine prophylaxis: a systematic review and meta-analysis of randomised controlled trials (2022) — Probiotics
• 6 Effects of probiotic supplementation on performance of resistance and aerobic exercises: a systematic review (2023) — Probiotics
• 7 Metagenomic Characterisation of Gut Microbiota in Children with Autism Spectrum Disorder: Microbial Signatures and Modulation by Anti-Inflammatory Diet (2025) — Chronic inflammation
• 8 Efficacy of Intestinal Obstruction Catheter Combined with Modified Dachengqi Decoction in Elderly Patients with Early Postoperative Inflammatory Intestinal Conditions (2026) — Chronic inflammation
• 9 Gut microbiota and the kidney-gut-skin axis in chronic kidney disease-associated pruritus: mechanisms and therapeutic implications (2026) — Chronic inflammation
• 10 Design of a randomised controlled trial of zinc supplementation to improve markers of mortality and HIV disease progression in HIV-positive drinkers (2018) — Zinc
• 11 The Role of Zinc in Paediatric Respiratory Infections: Evidence from Clinical Trials and Real-World Studies (2026) — Zinc
• 12 Zinc Supplementation, Inflammation, and Gut Integrity Markers in HIV Infection: A Randomised Placebo-Controlled Trial (2025) — Zinc
• 13 Vitamin D Deficiency as a Context-Dependent Modifier of Osteonecrosis of the Jaw (2026) — Vitamin D
• 14 Vitamin D Endocrine System and COVID-19: Treatment with Calcifediol (2022) — Vitamin D
• 15 Differential Expression of Proteins Involved in Skin Barrier Maintenance and Vitamin D Metabolism in Atopic Dermatitis: A Cross-Sectional, Exploratory Study (2024) — Vitamin D
• 16 Curcumin and Tetrahydrocurcumin as Multi-Organ Modulators of the Adipose Tissue-Gut-Liver Axis: Mechanistic Insights, Therapeutic Potential, and Translational Perspectives (2025) — Turmeric and Curcumin
• 17 Impaired Postprandial GLP-2 Response Enhances Endotoxaemia, Systemic Inflammation, and Kidney Injury in Metabolic Dysfunction-Associated Steatohepatitis (2024) — Turmeric and Curcumin
• 18 Enhanced Bioavailability of a Novel Double-Layered Nano-Liposomal Curcumin (BNT-C060): A Randomised, Double-Blind, Clinical Trial (2026) — Turmeric and Curcumin
• 19 Potential Modulation of Inflammation by Probiotic and Omega-3 Supplementation in the Elderly with Chronic Low-Grade Inflammation: A Randomised, Placebo-Controlled Trial (2022) — Omega-3 Fatty Acids
• 20 Integrating Nutrition into Precision Medicine for Controlling Systemic Inflammation in Rheumatoid Arthritis (2025) — Omega-3 Fatty Acids
• 21 Current Research and Future Prospects of Immunonutrition in Gastrointestinal Malignancies (2024) — Omega-3 Fatty Acids
• 22 Effect of Dapagliflozin and Magnesium Supplementation on Renal Magnesium Handling and Magnesium Homeostasis in Metabolic Syndrome (2021) — Magnesium
• 23 <i>HNF1B</i> Transcription Factor: Key Regulator in Renal Physiology and Pathogenesis (2024) — Magnesium
• 24 Association of Hypomagnesaemia with Liver Injury, Role of Gut-Barrier Dysfunction and Inflammation: Efficacy of Abstinence and 2-Week Medical Management (2022) — Magnesium

5. Open Questions

• Humic Acid Complexes: Are there dose-dependent effects on the human gut barrier?
• Combination Therapies: Do substances such as zinc + vitamin D or probiotics + omega-3 act synergistically?
• Long-Term Effects: How stable are changes to the gut barrier after discontinuation of these substances?
• Individual Factors: What role do genetics, microbiome composition, or pre-existing conditions play?
• Biomarkers: Which parameters are best suited for measuring gut barrier function in clinical practice?

See also the gap list for all substances. This page is recalculated with each update.