🧱 Leaky Gut: What the Evidence Actually Supports

By Sam, Founder of FarmFitUSA · Researched and written in-house · Last reviewed August 2026

Intestinal permeability is a real, measurable phenomenon studied in serious medicine. Whether it causes the conditions attributed to it is a separate question.

Intestinal permeability is a real, measurable phenomenon studied in serious medicine. Whether it causes the conditions attributed to it is a separate question.

The Barrier Is Real

Your intestinal lining is a single layer of epithelial cells separating gut contents from your bloodstream. Given the surface area involved, this is one of the most consequential barriers in the body.

Cells are joined by tight junctions — protein complexes including occludin, claudins and zonula occludens. These are not permanent seals. They open and close in a regulated way to allow selective passage, and their regulation is genuinely dynamic.

Zonulin is the best-known regulator, identified by Alessio Fasano's group. Gliadin, a wheat protein, triggers zonulin release, which opens tight junctions. This is real, published work, and it is the mechanistic basis of much of the field.

So "intestinal permeability" is not a fringe concept. It is measurable, it is regulated, and it is studied in mainstream gastroenterology.

Where the Evidence Is Solid

Increased permeability is documented in specific conditions:

Coeliac disease. Well established. Gluten drives permeability in genetically susceptible people, and the mechanism is characterised.

Inflammatory bowel disease. Increased permeability is documented in Crohn's disease, and notably in some first-degree relatives before disease onset — which is one of the more interesting findings, since it suggests permeability may precede rather than merely follow inflammation.

Critical illness, burns, major trauma, severe sepsis. Gut barrier failure is a recognised clinical problem and a target of research in intensive care.

NSAID enteropathy. Non-steroidal anti-inflammatory drugs demonstrably increase permeability. This is one of the clearest and most modifiable causes.

Alcohol. Increases permeability, and this is part of the mechanism of alcoholic liver disease.

Chemotherapy and radiation.

Endurance exercise in heat. Blood shunted away from the gut increases permeability transiently — well documented in athletes.

Where It Is Contested

The popular claim is broader: that leaky gut is widespread, and that it causes autoimmune disease, allergies, asthma, depression, anxiety, skin conditions, chronic fatigue and joint pain by allowing food particles and bacterial products into the bloodstream.

The problem is direction of causation. Increased permeability is observed alongside many conditions. What is much harder to establish is whether it causes them, results from them, or shares a common upstream cause.

For coeliac disease the mechanism is worked out. For most of the conditions on the popular list, permeability is an association whose direction is not established. Many gastroenterology bodies have been cautious for this reason — not because the phenomenon is fake, but because the causal claim outruns the data.

Testing is a genuine weak point. Lactulose-mannitol ratio testing is used in research and is reasonably validated for measuring small intestinal permeability, though it is affected by transit time and kidney function. Serum zonulin testing, widely sold direct to consumers, has been criticised on the grounds that commercial assays may not be measuring zonulin specifically. A positive result from those tests should not be treated as a diagnosis.

What Actually Increases Permeability

Practical, evidence-supported, and mostly modifiable:

NSAIDs. Regular ibuprofen, naproxen and aspirin. Among the clearest causes and the easiest to change.

Alcohol, dose-dependently.

Untreated coeliac disease. If you have unexplained gut symptoms, get tested before removing gluten — testing requires gluten in the diet.

Chronic significant stress, via HPA-axis effects on barrier function.

Acute infection, including food poisoning. Post-infectious IBS is real.

Very low fibre intake. Fibre-starved bacteria degrade the protective mucus layer, which is a genuinely interesting mechanism from mouse work.

What Actually Helps

Ranked by strength of evidence.

Remove the cause. Stop unnecessary NSAIDs, moderate alcohol, treat coeliac disease if present. This is the intervention with real evidence.

Fibre and fermentable substrate. Butyrate, produced by bacterial fermentation of fibre, is the primary fuel for colonocytes and supports barrier function. Feeding your bacteria properly is the best-supported dietary approach. See Probiotics.

Adequate protein, particularly glutamine. Glutamine is a preferred fuel for enterocytes, and it has evidence in specific clinical settings such as burns and critical illness. Whether supplementation helps otherwise healthy people is far less clear.

Zinc. Zinc deficiency impairs barrier function, and repletion improves permeability in deficiency states. Worth checking if you are likely deficient; less compelling otherwise.

Vitamin D. Involved in tight junction regulation. See Vitamin D Mastery.

Sleep and stress management, with plausible mechanism and modest direct evidence.

Mucilaginous herbs. Slippery elm, marshmallow root, aloe and mimosa pudica coat the mucosa. The demulcent effect is real; barrier repair claims are not established. See Slippery Elm, Marshmallow Root, Mimosa Pudica Seed.

Collagen and bone broth. Popular and mechanistically plausible via amino acid supply. Direct human evidence for barrier repair is thin. Both are perfectly good food. See Bone Broth, Collagen Protocols.

What To Be Careful Of

"Leaky gut protocols" that cost hundreds of pounds and rest on a test that may not measure what it claims.

Elimination diets that keep expanding. Progressive restriction is a real harm — nutritional inadequacy, social cost, and in some people a slide into disordered eating.

Attributing everything to it. If you have significant symptoms, they deserve a diagnosis. Coeliac disease, IBD, SIBO, bile acid malabsorption, thyroid disease and pancreatic insufficiency all have specific tests and specific treatments, and all get missed when everything is labelled leaky gut.

The Honest Summary

Intestinal permeability is real, measurable, and increased in a defined set of conditions with characterised mechanisms. It is a legitimate area of research.

The broad claim that leaky gut causes most modern chronic illness is not established, direction of causation is usually unresolved, and the commercial tests sold to diagnose it are not reliable enough to act on.

The things that genuinely help — stopping NSAIDs, moderating alcohol, eating fibre, treating coeliac disease, sleeping — are unglamorous, cheap, and good for you regardless of what you call the mechanism.

REFERENCES

• Published research on intestinal barrier function, tight junction regulation and zonulin, including work by Fasano and colleagues.
• Reviews of intestinal permeability in coeliac disease and inflammatory bowel disease.
• Research on NSAID enteropathy and alcohol-induced intestinal permeability.
• NIH National Center for Complementary and Integrative Health, information on digestive supplements.
• Published critiques of commercial serum zonulin assays.

How to Buy Smart

Quality varies enormously between suppliers, and with powders and dried material you usually cannot tell by looking. Buy from someone who states the species, the plant part, the country of origin and a harvest or best-before date. Vague labelling almost always means a commodity blend.

We use the Starter Detox Bundle from CleanseParasites for this. No affiliate arrangement — we link where we actually shop.

Common Questions

Is leaky gut real?

Increased intestinal permeability is real, measurable and documented in coeliac disease, IBD, critical illness, NSAID use and alcohol exposure. The broader claim that it causes most chronic illness is not established.

Is the zonulin test reliable?

Commercial serum zonulin assays have been criticised on the basis that they may not be measuring zonulin specifically. A result from one should not be treated as a diagnosis.

What increases permeability most?

Regular NSAID use and alcohol are among the clearest and most modifiable causes. Untreated coeliac disease is another.

Does bone broth heal the gut lining?

It is plausible via amino acid supply and it is good food, but direct human evidence for barrier repair is thin. Fibre, which feeds butyrate-producing bacteria, has better support.

Should I do an elimination diet?

Only in a structured, time-limited way with reintroduction. Progressive restriction risks nutritional inadequacy and disordered eating, and it delays finding a real diagnosis.

Educational and informational purposes only. FarmFitUSA content is not medical or veterinary advice and is not intended to diagnose, treat, remedy, or prevent any disease. These statements have not been evaluated by the FDA. Consult a qualified professional before acting on anything here, and call a vet or a doctor when the situation warrants it.