"Leaky gut" — or increased intestinal permeability — has become one of the most discussed topics in functional and integrative medicine. Researchers can measure increased intestinal permeability in some conditions, but the direction and clinical significance of associations vary. "Leaky gut" is not itself a medical diagnosis, and symptoms alone cannot establish increased permeability.
What Is Leaky Gut?
Your intestinal lining is held together by tight junction proteins that form a selective barrier. When functioning properly, this barrier allows nutrients to pass through into the bloodstream while keeping out harmful substances like undigested food particles, bacterial endotoxins (lipopolysaccharides), and pathogens. When these tight junctions become loose or damaged, the barrier becomes "leaky," allowing substances to pass through that trigger immune and inflammatory responses.
A note on terminology is worth making up front. "Leaky gut" is the popular name; in the scientific literature the phenomenon is described as increased intestinal permeability or intestinal barrier dysfunction. Researchers have documented that the barrier can indeed become more permeable, and that this is observed in conditions such as inflammatory bowel disease and celiac disease.
What remains debated is how often increased permeability is a primary cause of symptoms versus a consequence of another underlying problem, and "leaky gut" is not itself a formal medical diagnosis. The practical takeaway is that barrier function is real and measurable, but it should be interpreted carefully and in context rather than treated as a catch-all explanation.
What Causes the Gut Barrier to Break Down?
Intestinal permeability has many potential contributors, which is part of why it can be hard to pin down. Commonly discussed factors include:
- Chronic gut infections and dysbiosis (an imbalance between beneficial and opportunistic microbes)
- Diets low in fiber and high in ultra-processed foods
- Chronic stress
- Heavy or frequent alcohol use
- Certain medications, such as NSAIDs
- Depletion of the fiber-fermenting bacteria that produce butyrate — a short-chain fatty acid that serves as the primary fuel for the cells lining the colon
The causes overlap and feed into one another. Working out which are at play for a given person usually means looking at the gut as a whole, not at permeability alone.
Sign 1: Multiple Food Sensitivities
Food reactions have many possible explanations, including allergies, intolerances and celiac disease. They are not a reliable sign of altered intestinal permeability; discuss persistent or concerning reactions with a clinician.
Sign 2: Autoimmune Conditions
Research led by Alessio Fasano and others has proposed that increased permeability is one contributing factor in the development of autoimmune disease. It sits alongside two others: a genetic predisposition, and an environmental trigger. Barrier function is one of the gut-related factors a practitioner may consider if you have been diagnosed with an autoimmune condition — Hashimoto's thyroiditis, rheumatoid arthritis, type 1 diabetes, celiac disease or lupus among them.
This is a model of biological mechanism rather than a guarantee that addressing the gut will resolve an established autoimmune condition. We cover this relationship in more depth in our article on the gut-autoimmune connection.
Sign 3: Chronic Skin Issues
Researchers are exploring gut–skin associations, but eczema, psoriasis, acne and rosacea have multiple causes. None is a diagnostic sign of increased intestinal permeability.
Sign 4: Brain Fog and Fatigue
Brain fog and fatigue are nonspecific symptoms. Sleep problems, anemia, thyroid disorders, medications and other conditions may explain them; neither establishes intestinal-barrier dysfunction.
Sign 5: Digestive Symptoms That Do Not Respond to Basic Treatment
If you have tried dietary changes, probiotics, and basic gut protocols without lasting improvement, a compromised gut barrier may be one of several underlying issues worth investigating before other interventions can be effective. Persistent bloating, irregular bowel habits, and food reactions that do not settle with simple measures are a reasonable prompt to look more systematically at what is happening in the gut.
A Word of Caution About Self-Diagnosis
It is important to recognize that every symptom on this list is non-specific — meaning it can be caused by many things that have nothing to do with intestinal permeability. Fatigue, brain fog, skin issues, and digestive complaints can stem from thyroid problems, anemia, sleep disorders, mental-health conditions, and a long list of other causes.
The presence of these signs does not confirm leaky gut, and important conditions can be missed if symptoms are attributed to it prematurely. The sensible path is to treat these signs as a reason to investigate with a clinician, not as a self-diagnosis.
What May Support a Healthy Gut Barrier
Research on supporting intestinal barrier function is ongoing, but several themes recur in the literature. Commonly discussed are:
- Adequate dietary fiber, which feeds the bacteria that produce butyrate, the short-chain fatty acid that fuels the cells of the colon lining
- Diets rich in whole, minimally processed foods
- Managing chronic stress
- Moderating alcohol
- Limiting unnecessary use of gut-irritating medications such as NSAIDs
- Certain nutrients and probiotics, which have been studied for barrier support as well
None of these are guaranteed fixes, and the right combination depends on the individual. That is why identifying the specific drivers in your own gut — ideally with testing and a knowledgeable practitioner — tends to be more productive than applying a generic protocol.
How Intestinal Permeability Is Assessed
There is no single perfect test for barrier function, and clinicians use several approaches. Historically, research has used the lactulose-mannitol urine test, which measures how much of two ingested sugar molecules cross the gut wall. More recently, blood and stool markers have been used as practical proxies.
Stool zonulin is an optional marker reported with GI-MAP™ + Zonulin. Its usefulness for establishing increased intestinal permeability is not settled; research on some commercial serum zonulin assays has raised specificity concerns, but does not directly evaluate this particular stool assay.
The GI-MAP™ + Zonulin package reports an additional stool zonulin measurement alongside selected microbial qPCR targets and separately measured intestinal-health markers. It does not directly test intestinal permeability, diagnose "leaky gut," or establish the cause of symptoms. A practitioner can interpret the findings alongside medical history and appropriate clinical testing.
If your symptoms point more toward a specific infection, our guides on H. pylori and on how molecular testing compares to conventional stool culture may help you decide where to start. You can review options and pricing or order a kit online when you are ready. As always, we recommend reviewing your results with a licensed practitioner — barrier markers guide a plan, they do not replace clinical judgment.
Sources
This article summarizes peer-reviewed literature on intestinal permeability. "Leaky gut" is not a formal diagnosis; discuss persistent symptoms with a licensed healthcare provider.
Assay-specific evidence: Scheffler et al. (2018) and Ajamian et al. (2019) identified specificity concerns in certain commercial serum zonulin assays. Neither examined this specific GI-MAP stool assay. Clinical review of this November 9 editorial revision is pending; historical review attribution does not imply approval of these revisions.
- Alterations in Intestinal Permeability: The Role of the "Leaky Gut" in Health and Disease (PMC)
- The Intestinal Barrier and Current Techniques for the Assessment of Gut Permeability (PMC)
- Fasano A. Intestinal permeability and its regulation by zonulin: diagnostic and therapeutic implications (PubMed)
- Intestinal Permeability in Inflammatory Bowel Disease: Pathogenesis, Clinical Evaluation, and Therapy of Leaky Gut (PMC)
Keep reading: zonulin, the gut-barrier marker · GI-MAP + Zonulin panel · how gut health testing works · how to read your report