Gluten, zonulin and “leaky gut”: what the research actually shows

The gluten-to-leaky-gut claim rests on real science, then takes a leap the evidence doesn’t support. Including one detail about the standard test that almost nobody mentions.

You have probably seen the post. Gluten triggers a protein called zonulin, zonulin pulls apart the tight junctions holding your gut lining together, that opens gaps for toxins to slip into your bloodstream, and therefore you should stop eating grains. There is usually a real citation attached, often to a researcher named Alessio Fasano.

The unusual thing about this claim is that almost every individual step is true. It is the conclusion that does not follow.

The parts that are real

Zonulin exists, and Fasano’s lab discovered it in 2000. It is a protein that regulates the tight junctions between the cells lining your intestine: essentially a dimmer switch for how permeable your gut wall is at any moment.

Gliadin, a fraction of gluten, really does trigger zonulin release. Increased intestinal permeability is genuinely well established in coeliac disease and in inflammatory bowel disease. And Fasano is a serious researcher, not a wellness influencer, and the paper usually cited is a real review in a real journal.

So far, so good.

Where the leap happens

Here is the part the posts leave out: gliadin triggers zonulin release in everyone. Not just in people with coeliac disease. Not just in the unwell.

Your gut is supposed to modulate its own permeability. Tight junctions open and close constantly as part of normal digestion and immune surveillance. A transient, measurable rise in permeability after eating bread is not damage. In most people it is the system doing its job.

Going from "this mechanism exists" to "therefore avoid grains" skips the step where you demonstrate the effect is large enough, and lasting enough, to matter clinically in people who don’t have coeliac disease or non-coeliac gluten sensitivity. That step has not been convincingly made.

It is also worth noticing what the broader evidence points at. Large cohort studies consistently associate higher whole-grain intake with lower inflammatory markers and lower all-cause mortality, the opposite direction from what "grains damage your gut" would predict.

The detail almost nobody mentions

If you follow this rabbit hole, you will eventually be told to get your zonulin measured. Many clinics sell exactly that test.

In 2018, a team led by Scheffler published something awkward in Frontiers in Endocrinology: the widely used commercial zonulin ELISA does not appear to detect zonulin at all. Using antibody capture, mass spectrometry and Western blot, they found the assay does not bind pre-haptoglobin-2, the actual molecule, and instead recognises properdin and structurally related proteins.

Sit with that for a second. A large amount of the "zonulin correlates with disease X" literature, and a great many commercial test results, rest on an assay that may not measure the thing printed on the box.

This is why Mura does not recommend a serum zonulin test, and why we would gently suggest treating any result you have already paid for as unreliable rather than alarming.

While we are here: IgG food sensitivity panels deserve the same scepticism. IgG antibodies to a food generally indicate exposure and tolerance, evidence you have eaten it, not that it is harming you. The American Academy of Allergy, Asthma and Immunology explicitly advises against ordering them. They tend to return long lists of false positives, which is how people end up eliminating fifteen foods for no reason.

Does any of this matter for mood?

Plausibly, yes, and this is worth stating carefully, because it is the part we care about most.

There is a real and actively researched link between intestinal inflammation, systemic inflammation and mood. We have written about the gut-brain axis and how it shapes how you feel separately. But two honest caveats belong on it.

First, much of the human evidence is associational. Second, increased permeability often turns out to be a consequence of inflammation rather than its trigger, which flips the causal story that "leaky gut causes your depression" depends on.

The gut is very likely part of the picture. It is not established as the root of it.

What to do instead

If your gut symptoms are real and persistent, they are worth taking seriously, just with better tools than a zonulin panel.

Stool calprotectin is a validated marker of actual intestinal inflammation, and it is the test that would tell you something. hsCRP gives a read on systemic inflammation. And if a specific food genuinely seems to be involved, talk to a GP or dietitian before removing food groups.

That last point is not bureaucratic caution. Supervised elimination gives you a usable answer; doing it alone usually gives you a smaller diet and no information. And if you have arrived here because your mood is low, it is worth knowing that restrictive eating and low mood interact badly, and that is a combination best navigated with support rather than a social media protocol.

Mura is a screening and education tool, not a diagnosis. Our gut screen flags patterns worth discussing with a clinician. It does not tell you that you have leaky gut, because that is not a diagnosis a questionnaire can make.

This article is for general information and is not a substitute for professional care. If you are in crisis or thinking about harming yourself, please contact your local emergency services or a crisis line. See crisis lines.