Leaky Gut: Real Science vs. Marketing Hype

What Is Intestinal Permeability?

The gut lining is a single-cell-thick barrier that selectively controls what enters your bloodstream. Tight junction proteins (zonulin, occludin, claudins) hold these cells together and regulate permeability.

Increased intestinal permeability (IIP) — when this barrier becomes more permeable than normal — allows larger molecules, bacterial fragments (lipopolysaccharides, LPS), and antigens to enter systemic circulation. This triggers immune activation and low-grade systemic inflammation.

IIP is a measurable clinical finding, associated with: - Inflammatory bowel disease (Crohn's, ulcerative colitis) - Coeliac disease - Type 1 diabetes - Liver disease (particularly alcoholic liver disease) - Critical illness and sepsis - Some autoimmune conditions

What 'Leaky Gut Syndrome' Is and Isn't

The alternative health industry has taken the genuine science of intestinal permeability and dramatically overextended it.

'Leaky gut syndrome' as marketed claims that IIP causes a vast array of conditions — chronic fatigue, autism, depression, fibromyalgia, autoimmune disease, food sensitivities — via a single mechanism.

The problem: While IIP is associated with many conditions, causation vs. correlation is rarely established. For most conditions listed, IIP may be a consequence of the disease, not a cause.

The evidence base for treating diverse chronic conditions via 'healing the gut lining' with supplements is thin.

What Drives Increased Intestinal Permeability?

Things with good evidence: - Chronic NSAID use (ibuprofen, aspirin) — direct damage to the mucosal layer - Alcohol excess — directly increases permeability - Psychological stress — CRH (corticotropin-releasing hormone) increases mast cell activation, which disrupts tight junctions - Dysbiosis / antibiotic overuse — altered microbiome reduces butyrate production, which normally maintains barrier integrity - Highly processed food diet — emulsifiers (particularly polysorbate-80 and carboxymethylcellulose) shown in animal studies to disrupt mucosal barrier and alter microbiome - Coeliac disease — gliadin (a gluten protein) directly activates zonulin, increasing permeability

Supplements With Evidence for Barrier Integrity

L-Glutamine

The primary fuel for enterocytes (intestinal epithelial cells). In situations of high metabolic demand (critical illness, post-surgery, heavy training), glutamine supplementation has been shown to maintain gut barrier function.

Evidence in healthy individuals with IIP is less clear. Most studies are in hospitalised patients.

Dose: 5–10g daily. Likely most relevant post-illness, post-antibiotic, or during heavy training blocks.

Butyrate / Butyrate Precursors

Short-chain fatty acid produced by gut bacteria fermenting fibre. The primary energy source for colonocytes (cells lining the colon). Maintains barrier integrity and has anti-inflammatory effects.

Increasing butyrate: Eat more resistant starch, inulin, pectin, and fibre-rich vegetables. Butyrate supplement capsules exist but evidence for therapeutic use vs. dietary butyrate is limited.

Probiotics (Specific Strains)

Lactobacillus rhamnosus GG has the strongest evidence for gut barrier maintenance — particularly in post-antibiotic gut recovery and traveller's diarrhoea. It increases tight junction protein expression in vitro.

Zinc Carnosine

A specific chelated compound (zinc + carnosine) that has been shown in RCTs to reduce gastric mucosal damage and improve gut integrity. Particularly relevant for NSAID users or those with alcohol-related gastric damage.

Dose: 75mg zinc carnosine twice daily.

Curcumin (with Piperine)

Anti-inflammatory effects in the gut mucosa have been demonstrated in Crohn's and UC. Evidence for IIP in healthy individuals is limited.

The Dietary Approach (Strongest Overall Evidence)

1. Reduce ultra-processed foods (emulsifiers, artificial sweeteners) 2. Eat diverse plant foods — 30+ different plants per week is a useful target for microbiome diversity 3. Include fermented foods — yoghurt, kefir, sauerkraut, kimchi 4. Limit alcohol 5. Manage chronic stress (this is a genuine GI issue, not just advice)

Bottom Line

Intestinal permeability is real and matters clinically in specific conditions. 'Leaky gut syndrome' as a catch-all diagnosis for everything is not supported by evidence.

If you suspect gut issues, work with a registered dietitian or gastroenterologist — not a supplement company.

Always see your GP for new or persistent digestive symptoms. Don't self-diagnose gastrointestinal conditions.