Glossary · Dysbiosis and disease
Intestinal permeability
In one sentence
Intestinal permeability is how easily substances in the gut lumen cross the intestinal lining into the bloodstream. It is a normal, regulated property; increased permeability is associated with several diseases.
Also known as: leaky gut · increased intestinal permeability · gut permeability · intestinal barrier function
What is intestinal permeability?
The gut has to absorb water and nutrients while keeping out bacteria, toxins and antigens. That dual role depends on the intestinal barrier: the mucus layer, the epithelium with its tight junctions between cells, antimicrobial substances and the immune system of the gut lining.
Permeability is a measurable property of that barrier. A 2014 review by Bischoff and colleagues in BMC Gastroenterology distinguishes the “intestinal barrier” (the structure) from “intestinal permeability” (its functional feature). The same review notes that both terms are used loosely and that their clinical significance is not yet clearly established.
What it is linked to
Increased permeability has been described in coeliac disease, inflammatory bowel disease, critical illness, food allergy, irritable bowel syndrome, and obesity with metabolic disease. A common hypothesis is that luminal components crossing the barrier activate the immune system and contribute to low-grade inflammation. It is also connected with dysbiosis, although which comes first is often unclear.
The popular term “leaky gut” is frequently used to explain a wide range of symptoms. That extrapolation is not supported by current evidence.
How it is measured
- Sugar absorption tests: the person drinks a solution of lactulose and mannitol (or rhamnose), and urine is collected over several hours. A raised lactulose/mannitol ratio suggests greater permeability. These are the reference tests, although diet, kidney function and gut transit affect the result.
- Indirect markers: zonulin, LPS-binding protein, intestinal fatty acid-binding protein (I-FABP) and citrulline, among others. None is validated as a standalone diagnostic test.
- Markers of local inflammation, such as faecal calprotectin, which do not measure permeability but help put it in context.
Example
A gastroenterologist is assessing a patient with coeliac disease who still has symptoms despite a gluten-free diet. Alongside checking dietary adherence, she arranges a dual-sugar permeability test and a faecal calprotectin. A raised indirect marker would be treated as supportive information only, never as the sole basis for a decision.
Intestinal permeability at Xenogene
Xenogene offers zonulin testing by ELISA, on stool or serum, as accessory data within the gut axis and never as an isolated diagnosis. Within the integrated profiles, the Sophia assistant places it in context with the clinical picture and validated markers, recommending correlation with faecal calprotectin and, where appropriate, with dual-sugar tests. Interpretation rests with the healthcare professional who requests it.
Frequently asked questions
Is leaky gut syndrome a real diagnosis?
Not as a condition in its own right. Increased intestinal permeability has been documented in diseases such as coeliac disease and inflammatory bowel disease, but "leaky gut syndrome" as a standalone diagnosis is not recognised in mainstream medicine.
How is intestinal permeability tested?
The classic reference method is a sugar absorption test, such as lactulose/mannitol, which measures in urine how much of each ingested sugar has been absorbed. Blood and stool markers exist, such as zonulin, but their validity is debated.
What increases intestinal permeability?
Reported factors include infections, some medicines (for example NSAIDs), alcohol, strenuous exercise and critical illness. Their effect is often temporary, and its clinical relevance depends on the context.
Related terms
- Zonulin
Zonulin is a human protein, identified as prehaptoglobin-2, that reversibly regulates tight junctions in the intestinal lining. It has been proposed as a marker of intestinal permeability.
- Dysbiosis
Dysbiosis is a change in the composition or function of the microbiota away from what is considered compatible with health: loss of diversity, loss of beneficial microbes or overgrowth of others.
- Low-grade inflammation
Low-grade inflammation is a mild, persistent, systemic inflammatory activation with no acute infection or injury to explain it. It is detected through modest rises in markers such as high-sensitivity CRP.
- Faecal calprotectin
Faecal calprotectin is a neutrophil protein measured in stool as a marker of inflammation of the intestinal lining. It helps distinguish inflammatory bowel disease from functional disorders such as irritable bowel syndrome.
Educational content for healthcare professionals and the general public. It does not replace assessment by a healthcare professional: ordering and interpreting any test is the responsibility of the requesting clinician.
Updated on