Leaky gut — medically termed intestinal hyperpermeability — exists as a genuine physiological phenomenon, though it has been significantly over-marketed in wellness culture. This guide separates the genuine science from the supplement marketing to give an accurate picture of what the evidence supports.
What intestinal permeability is
The intestinal epithelium — a single-cell layer lining the gut — controls what passes between the gut contents and the bloodstream. When tight junction proteins connecting adjacent cells are disrupted (by inflammation, stress, certain dietary compounds, or dysbiosis), larger molecules including bacterial components can cross into the bloodstream, triggering immune activation. This is the physiology behind leaky gut — real and documented, particularly in coeliac disease and inflammatory bowel disease.
What the evidence does and doesn't support
Intestinal hyperpermeability is documented in coeliac disease, inflammatory bowel disease, critical illness, and with certain medications including NSAIDs. The claim that leaky gut underlies virtually all chronic conditions — as widely marketed in wellness contexts — is not supported by current evidence. The supplements commonly marketed for leaky gut repair (L-glutamine, zinc carnosine, digestive enzyme blends) have varied and often weak evidence bases in healthy adults.
Evidence-based dietary support
Short-chain fatty acids — particularly butyrate, produced by gut bacteria fermenting dietary fibre — are the primary fuel for colonocytes and support tight junction integrity. A high-fibre, diverse-plant diet is the most evidence-based approach. Zinc (from meat, shellfish, legumes, seeds) is required for tight junction protein synthesis. Reducing alcohol (which directly increases intestinal permeability) and managing chronic stress (which alters gut motility and epithelial function) support barrier integrity.
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Frequently asked questions
Is there a medical test for intestinal permeability?
Research tools for measuring intestinal permeability exist — including the lactulose-mannitol urine test and zonulin blood markers — but none are validated as routine clinical diagnostic tests in NHS practice. Zonulin in particular is often marketed directly to consumers but its clinical utility as a standalone diagnostic is contested in peer-reviewed literature. Any concerns about gut barrier function should be discussed with a gastroenterologist.
Which conditions have the strongest evidence for involving increased intestinal permeability?
The most robust evidence links intestinal hyperpermeability to coeliac disease, inflammatory bowel disease (Crohn's disease and ulcerative colitis), and critical illness. Increased permeability has also been documented in people taking regular NSAIDs and following significant alcohol consumption. The evidence for leaky gut as a driver of conditions such as autism, chronic fatigue, or autoimmune disease generally remains preliminary or contested.
Can stress cause leaky gut?
Chronic psychological stress does appear to influence gut barrier function. Stress hormones alter gut motility, affect the composition of the microbiome, and can modify tight junction protein expression. This is a genuine physiological relationship, though the clinical significance in otherwise healthy adults — as opposed to people with pre-existing gut conditions — is less clearly established.
Are there foods that directly damage the gut lining?
In susceptible individuals, gluten triggers epithelial damage in coeliac disease — the most clearly documented food-to-gut-lining mechanism. High alcohol intake increases intestinal permeability directly. In healthy adults without coeliac disease, the evidence that specific foods routinely damage the gut lining under normal dietary conditions is limited; the wellness-supplement narrative significantly overstates this.
What is the difference between dysbiosis and leaky gut?
Dysbiosis refers to an imbalance in the gut microbiome — a shift in the composition or diversity of bacteria colonising the intestinal tract. Leaky gut refers specifically to increased permeability of the intestinal epithelial barrier. The two can be related: certain dysbiotic states may reduce production of short-chain fatty acids that maintain barrier integrity, but they describe different phenomena and neither implies the other automatically.