Home/Leaky Gut
Condition Deep-Dive

Leaky Gut Syndrome

Increased intestinal permeability allows undigested food particles, toxins, and bacterial fragments to pass through the gut wall and into the bloodstream, triggering systemic inflammation, autoimmune conditions, and food sensitivities.

Linked to SIBO and Candida Tight Junction Dysfunction Nutrition Supports Repair

Last updated:

Definition

What Is Leaky Gut?

The intestinal lining is a single cell layer thick, but it's the most important barrier in your body. "Leaky gut" describes the breakdown of this barrier, allowing substances that should stay in your intestines to enter your bloodstream.

Healthy intestinal cells are connected by "tight junctions", protein complexes that control what passes between cells. When inflammation, pathogens, or dietary triggers damage these junctions, the spaces between cells widen, creating gaps.

Zonulin, a protein discovered by Dr. Alessio Fasano, is the primary regulator of tight junction permeability. Gluten and gut pathogens (including Candida and SIBO bacteria) trigger excessive zonulin release, opening tight junctions and initiating the leaky gut cascade.

๐Ÿ”ฌ Intestinal permeability is real and measurable, but the tests are not equally reliable. The lactulose/mannitol ratio is the better-validated method. Be careful with serum zonulin in particular: the widely used commercial ELISA has been shown not to detect pre-haptoglobin-2, the protein it is meant to measure, and to cross-react with properdin and complement C3. Stool calprotectin measures intestinal inflammation rather than permeability.3
Leaky gut, intestinal permeability illustration

Fasano's work established zonulin as the main physiological regulator of intestinal tight junctions, and proposed that when the zonulin pathway is deregulated in genetically susceptible people, autoimmune disorders can follow. That paper concerns autoimmune disease, and celiac in particular. It does not address SIBO or Candida.

โ€” on Fasano A. Leaky Gut and Autoimmune Diseases. Clin Rev Allergy Immunol. 2012;42(1):71โ€“781
Systemic Impact

How Leaky Gut Connects to Everything

When gut permeability increases, the downstream effects reach every organ system, making leaky gut a central factor in many seemingly unrelated conditions.

Common
increased permeability is often found alongside SIBO and Candida, though reliable prevalence figures do not exist2
Up to 50M
Americans live with an autoimmune condition on the most-quoted estimate, though NIH figures are closer to 24 million4
70%
of the immune system resides in gut-associated lymphoid tissue (GALT)5
๐Ÿซ€ Leaky Gut (Intestinal Hyperpermeability)
๐Ÿฆ 

Autoimmune Diseases

๐Ÿคง

Food Allergies & Sensitivities

๐Ÿ˜”

Depression & Anxiety

๐Ÿฆด

Joint Pain & Inflammation

๐ŸŒธ

Eczema & Skin Disorders

๐Ÿง 

Brain Fog & Neuroinflammation

โšก

Chronic Fatigue Syndrome

๐Ÿฉธ

Thyroid Disorders (Hashimoto's)

๐Ÿ’Š

Nutrient Deficiencies

Leaky Gut vs. SIBO: Symptom Category Overlap (Radar)
Signs & Symptoms

Leaky Gut Symptom Profile

Because leaky gut triggers systemic immune activation, symptoms extend far beyond the digestive tract, making it one of the most underappreciated root causes of chronic disease.

๐Ÿซ€ Digestive & Immune Symptoms

๐Ÿฅœ

Multiple Food Sensitivities (Growing List)

The hallmark symptom of leaky gut. When undigested food proteins enter the bloodstream through the damaged gut wall, the immune system mounts IgG antibody responses. Over time, patients develop reactions to an ever-growing list of foods, often starting with gluten and dairy, expanding to dozens of foods. The sensitivities are a symptom of leaky gut, not primary food allergies.

๐Ÿซ˜

Bloating, Gas & Digestive Discomfort

Impaired intestinal barrier function disrupts normal digestive enzyme production and peristalsis. Food ferments and produces gas. Unlike SIBO (bloating 30โ€“90 min after meals), leaky gut bloating can be persistent and unpredictable, often triggered by many different foods seemingly at random.

๐Ÿฆ 

Autoimmune Disease & Flares

Dr. Fasano's research demonstrates leaky gut is a prerequisite for autoimmune disease. When bacterial LPS fragments enter the bloodstream, the immune system may attack the body's own tissues (molecular mimicry). Linked to Hashimoto's, Rheumatoid Arthritis, Lupus, Type 1 Diabetes, and MS.

๐Ÿคง

Allergies, Asthma & Histamine Intolerance

A permeable gut floods the bloodstream with antigens that prime toward allergic (Th2-dominant) responses. Seasonal allergies worsen, asthma becomes more reactive, and histamine intolerance develops, causing hives, itching, flushing, and headaches from previously tolerated foods.

๐Ÿฉธ

Nutrient Deficiencies Despite Eating Well

Damaged intestinal villi become flattened and dysfunctional. Iron, B12, folate, zinc, fat-soluble vitamins (A, D, E, K), magnesium, and calcium are poorly absorbed even with a nutritious diet, causing deficiency symptoms despite adequate dietary intake.

๐Ÿง  Systemic & Neurological Symptoms

๐Ÿง 

Brain Fog & Neuroinflammation

Bacterial endotoxins (LPS) can penetrate the blood-brain barrier, triggering neuroinflammation. This directly causes brain fog, slow processing, memory issues, and cognitive fatigue. Microglial activation is now linked to leaky gut in Alzheimer's, Parkinson's, and depression.

๐Ÿ˜”

Depression, Anxiety & Mood Instability

LPS-driven inflammation suppresses serotonin synthesis, increases cortisol, and activates inflammatory cytokines (IL-6, TNF-ฮฑ) that cross the blood-brain barrier and cause depressive symptoms. Up to 35% of depression cases show elevated intestinal permeability markers.

๐Ÿฆด

Joint Pain, Inflammation & Fibromyalgia

Circulating immune complexes deposit in joints and tissues, triggering localized inflammation. Patients experience migratory joint pain, morning stiffness, and widespread muscle tenderness that can fulfill fibromyalgia criteria, and can resolve significantly with gut healing.

๐ŸŒธ

Chronic Skin Conditions

Circulating endotoxins trigger dermal inflammation manifesting as eczema, psoriasis, cystic acne, rosacea, and urticaria. Skin conditions that don't respond to topical treatments almost always have a gut root, particularly leaky gut, SIBO, or Candida.

๐Ÿ’Š

Hormonal Imbalance & Thyroid Dysfunction

When the liver is overwhelmed processing gut-derived endotoxins, it fails to properly clear excess estrogen and thyroid antibodies. Leaky gut is a key driver of Hashimoto's thyroiditis, estrogen dominance, PCOS, and adrenal dysregulation.

Diagnosis

How to Test for Leaky Gut

Leaky gut is now measurable and testable, not just theoretical.

๐Ÿ  At-Home Indicators

๐Ÿฅฃ The Food Reaction Journal

Keep a detailed food and symptom diary for 2 weeks. Note every food eaten and symptoms (fatigue, brain fog, bloating, skin reactions, joint pain, mood changes) in the 2โ€“4 hours following. If you're reacting to many different food groups, not just one or two, this pattern of widespread food sensitivity strongly suggests leaky gut as the common thread.

๐Ÿงน The Elimination Diet Screen

Remove the 5 most common leaky gut triggers for 3โ€“4 weeks: gluten, dairy, alcohol, refined sugar, and processed foods. Significant improvement in energy, skin, brain fog, joint pain, or bloating during this elimination strongly suggests leaky gut. Reintroducing triggers one at a time confirms individual responses.

๐Ÿ“‹ Leaky Gut Symptom Score

Score 1 for each: reactions to multiple foods, autoimmune diagnosis, treatment-resistant skin conditions, migratory joint pain, worsening allergies, brain fog, chronic fatigue, anxiety/depression, nutrient deficiencies despite good diet, history of NSAID or antibiotic use, high chronic stress. Score 6+ strongly indicates leaky gut.

๐Ÿ”ฌ Lab & Clinical Tests

๐Ÿงช Lactulose/Mannitol Urine Test

The gold standard for measuring intestinal permeability. You drink a solution of lactulose (large molecule) and mannitol (small molecule), then collect urine for 6 hours. A high lactulose-to-mannitol ratio proves the gut wall is allowing large molecules through. Available through specialist laboratories.

๐Ÿฉธ Serum Zonulin Test

Zonulin is the protein that opens tight junctions. Elevated serum zonulin is a direct biomarker of increased intestinal permeability. Available through functional medicine labs. Best interpreted alongside symptoms and the lactulose/mannitol test.

๐Ÿงฌ Stool DNA Test

Measures calprotectin (intestinal wall inflammation) and secretory IgA (mucosal immune defense). Also identifies root causes driving the permeability, SIBO bacteria, Candida, H. pylori, parasites. Ordered through Diagnostic Solutions Lab via a functional medicine practitioner.

๐Ÿฉธ Intestinal Antigenic Permeability Panel

The most specific blood test for leaky gut. Measures antibodies against intestinal barrier proteins (actomyosin, occludin, claudin, zonulin), directly testing whether tight junction proteins are being attacked by the immune system. Available through specialist laboratories via a practitioner.

Treatment Comparison

Holistic vs. Conventional Treatment for Leaky Gut

๐ŸŒฟ HOLISTIC
๐Ÿ’Š CONVENTIONAL
๐ŸŒฟ

Holistic / Functional Approach

Remove triggers, rebuild the gut lining, restore the microbiome

Primary Strategy
4R Protocol: Remove, Replace, Reinoculate, Repair, systematically rebuilds gut integrity
Key Nutrients
L-Glutamine, Zinc Carnosine, Collagen, DGL Licorice, Butyrate, Vitamin A & D
Duration
3โ€“6 months for significant repair; ongoing dietary maintenance
Outcome
Reduced autoimmune activity, fewer food reactions, improved energy and mood

Core Healing Protocol

  • L-Glutamine (5โ€“10g/day fasted): Primary fuel for enterocytes (gut lining cells); directly repairs tight junctions
  • Zinc carnosine (75โ€“150mg/day): Binds to gut lining, reducing inflammation and accelerating mucosal healing. Zinc-carnosine is a chelate: 75 mg of it carries roughly 16 mg of elemental zinc, so do not count it as 75 mg of zinc when adding up your intake.
  • Collagen peptides (10โ€“20g/day): Provides proline, glycine, hydroxyproline for intestinal wall structural repair
  • DGL licorice (760mg before meals): Soothes inflammation in the intestinal mucosa. DGL means deglycyrrhizinated, the compound responsible for licorice's effects on blood pressure and potassium has been removed, which is why this form avoids them. Do not substitute whole licorice root or licorice confectionery, which do raise blood pressure and lower potassium.7
  • Slippery Elm bark (400โ€“500mg, 3x/day): Creates a protective mucilaginous layer over irritated gut lining
  • Marshmallow root, similar demulcent action; calms the gut lining
  • Butyrate (600mg/day): Short-chain fatty acid that feeds colonocytes and strengthens tight junctions
  • Remove all dietary triggers (gluten, dairy, alcohol, NSAIDs, processed food)
โœ… Holistic approach is well-tolerated with essentially no negative side effects. Healing is gradual and durable when triggers are removed.
Remove Phase

Foods & Factors That Cause Leaky Gut

You cannot heal a leaky gut while continuing to expose it to the triggers that caused it. The "Remove" phase is the foundation of all healing.

Dietary Triggers

  • โšกGluten (Gliadin): Directly triggers zonulin release in ALL people (not just Celiacs), opening tight junctions. The #1 dietary cause of leaky gut.
  • โšกDairy (Casein A1): A1 casein is processed into beta-casomorphin-7, which triggers gut inflammation similar to gluten. A2 dairy (sheep, goat) is better tolerated.
  • โšกAlcohol: Directly increases intestinal permeability within hours; disrupts protective mucus layer.
  • โšกRefined sugar & processed foods: Feed pathogenic bacteria and Candida; food additives (carrageenan, emulsifiers) directly disrupt tight junctions.
  • โšกIndustrial seed oils: Canola, soybean, corn oil, high omega-6, pro-inflammatory, damage the gut membrane.
  • โšกGMO foods / Glyphosate: Glyphosate disrupts tight junctions and the gut microbiome, choose organic where possible.

Non-Dietary Triggers

  • โšกNSAIDs (Ibuprofen, Aspirin): Directly damage the gut lining and inhibit prostaglandins needed for mucosal repair.
  • โšกProton Pump Inhibitors (PPIs): Reduce stomach acid, allowing bacteria to colonize the upper GI, perpetuating SIBO and leaky gut.
  • โšกAntibiotics: Wipe out protective bacteria, allowing pathogens to overgrow and damage the lining.
  • โšกChronic stress: Cortisol increases intestinal permeability via CRH (corticotropin-releasing hormone) signaling.
  • โšกInfections (SIBO, Candida, parasites): Pathogenic organisms directly degrade the intestinal lining and tight junction proteins.
  • โšกChronic sleep deprivation: Disrupts gut microbiome composition and increases inflammatory markers.
Nutritional Strategy

What to Eat

The section above covers what to remove. This one covers what to add, which is the half most often left out.

⚠️ What this section can and cannot claim. No diet has been shown to close a permeable intestinal barrier in humans, and there is no validated test to confirm it either way. What the evidence does support is that these foods change the gut microbiome and shift inflammatory markers. That is worth doing on its own terms, and it is a smaller claim than most of what is written about this topic.

🌾 Build meals around

  • A wide range of plants, not simply more fibre. Different plants feed different bacteria, and variety across the week does more than volume from one source
  • Fermented foods, live yoghurt, kefir, sauerkraut, kimchi, miso and tempeh
  • Cooked and cooled potato, rice and oats, which form resistant starch that colonic bacteria ferment to butyrate
  • Adequate protein, since the intestinal lining renews itself every few days and that renewal needs amino acids
  • Oily fish, for omega-3, two to three times a week
  • Polyphenol-rich foods, berries, olive oil, cocoa, green tea, herbs and spices

🧺 How to introduce it

  • Slowly. A sudden jump in fibre and fermented food commonly causes bloating and wind for a week or two
  • One change at a time, so you can tell what helped and what did not
  • Small and frequent beats large and occasional, a spoonful of sauerkraut daily rather than a jar on Sunday
  • If symptoms worsen sharply, particularly with bloating and wind, stop and read the SIBO guide, since fermentable fibre makes SIBO worse before it makes anything better
  • If you have a stricture, or any history of bowel obstruction, do not increase fibre without medical advice
💡 The most relevant trial, stated honestly. Thirty-six healthy adults were randomised for 17 weeks to a high-fibre or a high-fermented-food diet. The fermented-food group showed steadily increasing gut microbiota diversity and decreasing inflammatory markers. In the high-fibre group the primary outcome, a cytokine response score, was unchanged9. Two things follow. Fermented foods have the better evidence of the two here, and the study measured immune and microbiome markers in healthy people, not intestinal permeability in anyone symptomatic.
Repair Phase Supplements

Key Supplements for Healing Leaky Gut

These supplements directly target intestinal permeability, repairing tight junctions, soothing the gut lining, reducing inflammation, and restoring the mucosal barrier.

SupplementHow It Heals the Gut LiningSuggested DoseTimingNotes
L-GlutamineThe #1 leaky gut supplement. Primary fuel for enterocytes (gut lining cells), they cannot repair without adequate glutamine. Directly stimulates synthesis of tight junction proteins (Claudin, Occludin, ZO-1). Most evidence-backed supplement for intestinal permeability.5โ€“15g/dayFasted morning; between mealsPowder in water; pharmaceutical-grade
Zinc L-CarnosineThe carnosine chelate adheres physically to the intestinal mucosa, reducing inflammation, inhibiting NF-kB, and directly accelerating mucosal cell turnover and tight junction protein expression. Also protective against H. pylori and NSAID-induced gut damage.75โ€“150mg/day (standardized zinc-carnosine)With or between mealsA standardized zinc-carnosine form is the most researched form
Aloe Vera JuiceAcemannan (active polysaccharide) soothes gut wall inflammation, stimulates mucus production for a protective barrier, and supports tight junction integrity. One of the most gentle and effective daily gut lining soothers available.2โ€“4 oz/dayMorning fasted or before mealsInner leaf fillet only; avoid whole leaf (contains aloin laxative)
Saccharomyces BoulardiiRestores microbiome diversity; competes with pathogenic organisms that damage the gut lining; produces short-chain fatty acids that fuel colonocyte repair; directly reduces intestinal permeability as measured by lactulose/mannitol testing.5โ€“10 billion CFU/dayBetween mealsSafe to take during antimicrobial treatment
Digestive EnzymesReplaces digestive enzymes damaged by gut inflammation. Complete food digestion prevents undigested food particles from irritating and further opening tight junctions. Reduces the antigen load that triggers immune responses in leaky gut.1โ€“2 capsules per mealStart of each mealFull-spectrum formula: protease, lipase, amylase, lactase
Milk Thistle (Silymarin)Protects the liver, which is under enormous stress in leaky gut, processing constant endotoxin (LPS) influx from the damaged gut wall. Silymarin reduces hepatic inflammation, supports glutathione production, and accelerates liver regeneration.300โ€“600mg/day (80% silymarin)With dinnerParticularly important when SIBO or Candida is concurrent
TUDCAImproves bile flow, critical because bile emulsifies fats, supports fat-soluble vitamin absorption (severely impaired in leaky gut), and acts as an antimicrobial barrier in the small intestine. Also directly anti-inflammatory and liver-protective.250โ€“500mg/dayWith fat-containing mealsExcellent synergy with Milk Thistle for liver and bile support If you have gallstones, or have never been checked for them, agree this with your clinician first: gallstones are common and usually silent, and deliberately stimulating gallbladder contraction when stones are present can trigger biliary colic or block a bile duct.
NAC (N-Acetyl Cysteine)Replenishes glutathione, the master antioxidant depleted by chronic gut inflammation. Glutathione directly protects enterocytes from oxidative damage. NAC also disrupts biofilms of gut pathogens that perpetuate leaky gut.600โ€“1,200mg/dayAway from meals for biofilm action; or with meals for gut repairThe liver also clears LPS circulating from a permeable gut
Apple Cider Vinegar (ACV)Restores stomach acid, insufficient HCl is a root driver of leaky gut (bacteria survive to the small intestine when acid is low). ACV's acetic acid also has anti-inflammatory effects on the gut lining and supports digestion of proteins.1โ€“2 tbsp in water before meals15 minutes before mealsRaw, unfiltered "mother" ACV; dilute well to protect teeth
Curcumin (Turmeric Extract)Downregulates NF-kB, a central regulator of gut wall inflammation, and reduces inflammatory cytokines (IL-6, IL-1ฮฒ, TNF-ฮฑ) that contribute to tight junction breakdown. Trial evidence in humans for reducing intestinal permeability specifically is limited and mostly small.6500โ€“1,500mg/dayWith fat-containing mealsMust include piperine (5โ€“20mg) or be liposomal for absorption
Omega-3 Cod Liver Fish OilEPA and DHA are incorporated into cell membranes of enterocytes, improving their structural integrity. Omega-3s reduce the LPS-triggered inflammatory cascade and support the gut-brain axis. Cod liver oil also provides Vitamins A and D critical for mucosal integrity.2โ€“3g combined EPA+DHA/dayWith mealsIFOS-certified for purity; enteric-coated reduces fishy aftertaste
Vitamin D3, test 25-OH-D first and set the dose with your clinicianVitamin D receptors are present on every gut epithelial cell. D3 directly regulates E-cadherin and other tight junction proteins. Vitamin D deficiency is strongly correlated with increased intestinal permeability, autoimmune disease, and IBD. Correcting a deficiency may need a higher initial dose, which is a clinical decision.Test 25-OH-D first and set the dose with your clinicianWith fat-containing mealMonitor serum 25-OH-D with your clinician. Dosing limits: the adult tolerable upper intake level is 4,000 IU/day. The Endocrine Society treats 30 ng/mL as sufficient and prefers 40–60 ng/mL; the Institute of Medicine sets sufficiency at 20 ng/mL. Anything above that needs a blood test and a clinician, not a self-directed dose.
Vitamin K2 (MK-7)Works synergistically with Vitamin D3, directs calcium to bones rather than soft tissue. Also has direct anti-inflammatory effects in the gut. MK-7 form has the longest half-life, providing consistent activity from a single daily dose.200โ€“400 mcg/day (MK-7)With fat-containing meal; same time as D3MK-7 is the superior form (menaquinone-7) vs. MK-4 for daily dosing If you take a blood thinner, agree any vitamin K supplement with the clinician managing it before you start or stop: vitamin K interferes with some anticoagulant medicines, and changing your intake can destabilise your monitoring results. Keeping intake consistent matters more than avoiding it. Not all blood thinners are affected the same way, which is why this is a conversation with your prescriber.
Magnesium GlycinateSupports hundreds of enzymatic reactions involved in gut repair. Magnesium deficiency (extremely common in leaky gut patients) impairs enterocyte regeneration, reduces gut motility, and worsens inflammation. Glycinate form is best absorbed and gentlest on the gut.300โ€“500mg/dayBefore bedBest for sleep support and gut relaxation; does not cause loose stools at this dose. The upper intake level for supplemental magnesium is 350 mg/day; above that the usual effect is loose stools rather than harm, but it is worth knowing.
Magnesium CitrateSame gut repair benefits as glycinate but with a gentle osmotic laxative effect useful for leaky gut patients with concurrent constipation (methane SIBO, sluggish motility). Improves stool frequency and transit time, reducing toxic load on the gut wall.200โ€“400mg/dayBefore bed or with dinnerUse citrate form when constipation is a prominent symptom; reduce dose if stools become loose. The upper intake level for supplemental magnesium is 350 mg/day; above that the usual effect is loose stools rather than harm, but it is worth knowing.
Copper BisglycinateCopper is essential for lysyl oxidase, the enzyme that cross-links collagen and elastin in the intestinal wall. Deficiency (common when zinc is supplemented) impairs connective tissue repair of the gut wall. Bisglycinate form is well-tolerated and highly bioavailable.2โ€“4 mg/dayWith meals; away from high-dose zincEssential when supplementing zinc >30mg/day; maintain zinc:copper ratio of ~10:1
Activated CharcoalAdsorbs bacterial endotoxins (LPS), mycotoxins, and other gut-derived toxins circulating from the leaky gut before they can enter systemic circulation. Provides significant symptom relief during active gut healing and die-off reactions.1,000โ€“2,000mg/dayBetween meals; 2+ hours away from ALL supplements and medicationsRotate with bentonite clay (alternate days). Do not use long-term, can cause constipation. Use for 2โ€“4 week cycles.
Peppermint & Lemon OilEnteric-coated peppermint oil reduces gut spasms and inflammation in the small intestine. Lemon oil (food grade) has anti-inflammatory and antimicrobial properties that reduce pathogen burden on the gut lining. Both support healthy gut motility.0.2mL peppermint (enteric-coated) 2x/dayBefore mealsEnteric-coated capsules only, plain peppermint oil dissolves in the stomach
Prokinetic, Ginger Root or 5-HTPRestores gut motility impaired by intestinal inflammation. Proper motility prevents bacterial stagnation (which worsens leaky gut), supports complete food transit, and reduces fermentation load on the damaged intestinal wall. Critical for preventing SIBO relapse.Ginger: 500โ€“1,000mg; 5-HTP: 50โ€“100mgBefore bed on empty stomachDo not use 5-HTP with SSRI/SNRI medications. Ginger also has direct anti-inflammatory effects in the gut.
The Framework

The 4R Protocol for Gut Healing

The 4R Protocol is the gold-standard functional medicine framework for healing the gut, addressing all four phases systematically.

1

Remove

Eliminate dietary triggers (gluten, dairy, sugar, alcohol), infections (SIBO, Candida, parasites), NSAIDs, and other gut irritants.

2

Replace

Restore digestive capacity: Betaine HCl (stomach acid), digestive enzymes, bile acid support. Proper digestion prevents undigested food from irritating the gut lining.

3

Reinoculate

Restore beneficial bacteria with high-quality, multi-strain probiotics and prebiotic foods. Healthy microbiome diversity protects gut barrier integrity.

4

Repair

Active gut lining repair: L-Glutamine, Zinc Carnosine, Collagen, Butyrate, DGL Licorice, Vitamins A & D. This phase runs concurrently with all others.

๐Ÿ’ก The 4R protocol works best when all phases are addressed simultaneously, not sequentially. You don't wait to finish "removing" before starting to "repair." The phases overlap and reinforce each other throughout the healing journey.
Start Healing

Ready to Seal Your Gut and Reclaim Your Health?

Leaky gut is the foundation of most chronic health conditions. Healing it transforms energy, mood, immunity, and digestion simultaneously.

Explore IBS / IBD โ†’

References & Evidence Notes

Each numbered entry below is either a source you can follow or a note setting out what the evidence does and does not support. Both are numbered together so the markers in the text line up.

Last reviewed 26 August 2026. Supplement entries are cross-checked against the NIH National Center for Complementary and Integrative Health and the Linus Pauling Institute Micronutrient Information Center.8 This page is nutrition education, not medical advice, and it does not replace your doctor. Be clear about what is established here and what is not. Increased intestinal permeability is a real, measurable phenomenon, and it is found alongside a number of diseases. What is not established is that it causes them, or that "leaky gut syndrome" exists as a standalone diagnosis; in most conditions where both are present, the direction of cause is unresolved. Persistent digestive symptoms deserve a medical work-up rather than a supplement protocol, particularly if you have blood in the stool, unintentional weight loss, or symptoms that wake you at night.

  1. Fasano A. Leaky Gut and Autoimmune Diseases. Clin Rev Allergy Immunol. 2012;42(1):71–78. Springer. The paper identifies zonulin as the only physiologic modulator of intercellular tight junctions described so far, and argues that deregulation of the zonulin pathway in genetically susceptible individuals can permit autoimmune disorders. Its subject is autoimmune disease and celiac disease. It does not discuss SIBO or Candida, and it reports no figure for permeability in those conditions. ↩
  2. No reliable prevalence figure exists for increased intestinal permeability in SIBO or Candida overgrowth. The two are frequently discussed together and share risk factors, but there is no published study establishing a rate, and the "nearly 100%" figure circulated online does not trace to a primary source. ↩
  3. On the limits of serum zonulin testing: Scheffler L, et al. Widely used commercial ELISA does not detect precursor of haptoglobin2, but recognizes properdin as a potential second member of the zonulin family. Front Endocrinol. 2018;9:22. PMC5807381, and Ajamian M, et al. Serum zonulin as a marker of intestinal mucosal barrier function: May not be what it seems. PLoS One. 2019. PLOS One. The commercial assay does not detect pre-haptoglobin-2 and cross-reacts with other proteins, which means a large body of published "serum zonulin" results may not measure zonulin at all. The lactulose/mannitol dual-sugar ratio remains the better-validated approach. ↩
  4. The frequently quoted figure of 50 million Americans with autoimmune disease comes from advocacy-group estimates. The National Institutes of Health estimate is substantially lower, in the region of 24 million. Both figures count autoimmune disease as a whole; neither establishes intestinal permeability as a cause. ↩
  5. The figure that roughly 70 to 80% of the body's immune cells reside in gut-associated lymphoid tissue is a widely used approximation rather than a precisely measured value, and different sources state it differently. It is useful for conveying that the gut is a major immune organ, and should not be read as a precise measurement. ↩
  6. Curcumin's inhibition of NF-kB signalling and downstream inflammatory cytokines is well characterised in laboratory work. Human trial evidence for reducing measured intestinal permeability specifically is limited, and the trials are small. Standard curcumin also has poor oral bioavailability, which is why absorption-enhanced preparations are usually studied. See the NCCIH and Linus Pauling entries, ref. 8. ↩
  7. Deglycyrrhizinated licorice (DGL) has had glycyrrhizin removed, which is the constituent responsible for licorice's mineralocorticoid effects. Whole licorice and licorice confectionery raise blood pressure and lower potassium through that pathway and can cause serious hypokalaemia at sustained intakes, PubMed 42292819; DGL is used precisely to avoid this. The two are not interchangeable. ↩
  8. National Center for Complementary and Integrative Health (NIH), nccih.nih.gov, and the Linus Pauling Institute Micronutrient Information Center, lpi.oregonstate.edu/mic.
  9. Wastyk HC, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021;184(16):4137–4153. PubMed 34256014. A 17-week randomised study in healthy adults, 18 per arm. The high-fermented-food diet increased microbiota diversity and decreased inflammatory markers; in the high-fibre arm the primary outcome, a cytokine response score, was unchanged. The trial did not measure intestinal permeability. ↩