Should I get a zonulin test?

Probably not as a first step. The test results are often hard to interpret, the assay specificity is debated, and what you'd do based on the result (improve diet, address gut symptoms, rule out coeliac) you can do regardless. Useful as a research marker; less useful as a clinical guide for self-managing.

Is zonulin proof of leaky gut?

It's a marker that the gut barrier has loosened. 'Leaky gut' as a clinical diagnosis is still contested in mainstream medicine. The mechanism is real (intestinal permeability is measurable). Whether it's a cause of disease or a consequence of inflammation is what's debated.

Can I lower zonulin with supplements?

Mostly through diet rather than supplements. L-glutamine and zinc carnosine have small studies suggesting modest effects on gut barrier. Most other supplements (collagen, bone broth, slippery elm) have weak evidence. Fix the upstream triggers (alcohol, NSAIDs, gluten if you're sensitive) first.

Does intermittent fasting lower zonulin?

Direct human evidence is weak. Studies of Ramadan-type fasting showed almost no effect on gut permeability, and no human trial has shown that 16-hour fasting windows lower zonulin. A mucin and Akkermansia mechanism has been seen mainly in animal models. Treat any gut-barrier benefit as unproven in people.

Microbiome science

Zonulin

Also called: leaky gut marker, intestinal permeability marker

Zonulin is a protein produced by the gut lining that loosens the tight junctions between cells. When zonulin is released, the gut becomes temporarily more permeable. It's the most cited biomarker for 'leaky gut', though the science is more complex, many commercial tests measure related proteins rather than zonulin itself, and high levels are not yet proven to predict specific disease.

What zonulin actually does

Zonulin (technically pre-haptoglobin 2) was discovered by Alessio Fasano's team in 2000. It binds to receptors on gut lining cells and triggers the loosening of tight junctions, the protein bands that hold gut cells together and control what passes between them. This loosening is normal and useful, it helps with nutrient absorption and immune sampling. The question is whether chronically elevated zonulin contributes to disease.

What raises zonulin

Gluten (gliadin specifically): the most consistent trigger in research. Effect strongest in coeliac disease but measurable in non-coeliacs too.
Bacterial overgrowth in the small intestine (SIBO).
Acute infections: norovirus, salmonella, etc.
Heavy alcohol use.
NSAIDs (ibuprofen, naproxen) with prolonged use.
Acute stress through HPA axis activation.

The testing debate

Most commercial 'zonulin' tests measure a related protein (haptoglobin) using ELISA antibodies that may cross-react with several proteins. Independent researchers have shown that these tests don't always measure zonulin specifically. So a 'high zonulin' result on a stool or blood test should be interpreted carefully, it suggests something is altering gut permeability, but the specific molecule may not be zonulin itself. Monash University notes that current tests used to identify 'leaky gut' have significant limitations.

What 'high zonulin' might mean

Coeliac disease (zonulin clearly elevated in active disease).
Type 1 diabetes (zonulin tends to rise before diagnosis).
Inflammatory bowel disease (Crohn's, UC), at least during flares.
Non-alcoholic fatty liver disease.
Some autoimmune conditions (the link is associative, not causal yet).
Could also reflect normal day-to-day variation depending on what you ate yesterday.

How to lower it (if you're treating high results)

Cut gluten for 6 weeks if you haven't already; retest.
Address SIBO if breath testing is positive.
Eat more fermentable fibre to feed butyrate producers (butyrate strengthens the gut barrier).
Reduce alcohol substantially.
Stop unnecessary NSAIDs.
Eat polyphenol-rich foods (olive oil, berries, dark chocolate).
Sleep 7+ hours; short sleep may raise permeability markers, though human evidence is mixed.
Don't waste money on supplements claiming to 'seal the gut'. The evidence is poor.

Common questions

Should I get a zonulin test?: Probably not as a first step. The test results are often hard to interpret, the assay specificity is debated, and what you'd do based on the result (improve diet, address gut symptoms, rule out coeliac) you can do regardless. Useful as a research marker; less useful as a clinical guide for self-managing.
Is zonulin proof of leaky gut?: It's a marker that the gut barrier has loosened. 'Leaky gut' as a clinical diagnosis is still contested in mainstream medicine. The mechanism is real (intestinal permeability is measurable). Whether it's a cause of disease or a consequence of inflammation is what's debated.
Can I lower zonulin with supplements?: Mostly through diet rather than supplements. L-glutamine and zinc carnosine have small studies suggesting modest effects on gut barrier. Most other supplements (collagen, bone broth, slippery elm) have weak evidence. Fix the upstream triggers (alcohol, NSAIDs, gluten if you're sensitive) first.
Does intermittent fasting lower zonulin?: Direct human evidence is weak. Studies of Ramadan-type fasting showed almost no effect on gut permeability, and no human trial has shown that 16-hour fasting windows lower zonulin. A mucin and Akkermansia mechanism has been seen mainly in animal models. Treat any gut-barrier benefit as unproven in people.

Sources

Tripathi et al. Identification of human zonulin, a physiological modulator of tight junctions, as prehaptoglobin-2, 2009 (PNAS (PMC2744629))
Scheffler et al. Widely Used Commercial ELISA Does Not Detect Precursor of Haptoglobin2, but Recognizes Properdin as a Potential Second Member of the Zonulin Family, 2018 (Front Endocrinol (PMC5807381))
Ajamian et al. Serum zonulin as a marker of intestinal mucosal barrier function: May not be what it seems, 2019 (PLOS ONE (PMC6331146))
Lammers et al. Gliadin Induces an Increase in Intestinal Permeability and Zonulin Release by Binding to the Chemokine Receptor CXCR3, 2008 (Gastroenterology (PMC2653457))
Sapone et al. Zonulin Upregulation Is Associated With Increased Gut Permeability in Subjects With Type 1 Diabetes and Their Relatives, 2006 (Diabetes (PMID 16644703))
Pacifico et al. Increased circulating zonulin in children with biopsy-proven nonalcoholic fatty liver disease, 2014 (World J Gastroenterol (PMC4258579))
Peng et al. Butyrate Enhances the Intestinal Barrier by Facilitating Tight Junction Assembly via Activation of AMP-Activated Protein Kinase in Caco-2 Cell Monolayers, 2009 (J Nutr (PMC2728689))
Del Bo' et al. A polyphenol-rich dietary pattern improves intestinal permeability, evaluated as serum zonulin levels: the MaPLE randomised controlled trial, 2021 (Clin Nutr / BMC Geriatr (MaPLE, PMC11344393))
Gut permeability & IBS, do I really have a 'leaky' gut? (Monash University FODMAP)