What is leaky gut, and how much of the online version is real?

“Leaky gut” is a common gut-health phrase online, and also a confused one. Part of it is real physiology that researchers have measured for decades. Part of it is a wellness story that blames a hole in your gut for almost every chronic symptom and offers a multi-step protocol to patch it. This page pulls the two apart, using the human research rather than the marketing: what intestinal permeability actually is, what raises it, how it is (and is not) tested, which interventions have changed it in trials, and where the BPC-157 and peptide claims you keep seeing in gut-health threads really sit.

What is a leaky gut?

A leaky gut is a casual name for increased intestinal permeability, meaning the lining of the intestine lets more molecules pass through or between its cells than it normally would. A 2019 clinical review in Gut by Mayo Clinic gastroenterologist Michael Camilleri calls “leaky gut” a “simplistic term reflecting intestinal permeability,” a function that was extensively studied in gut diseases and reported in the literature from 1970 to 1990 (Camilleri, 2019).

The barrier itself is more than one layer of cells. The same review describes it as surface mucus, the epithelial cell layer and the immune defenses beneath it, and it notes that permeability can rise through the gaps between cells, through cells dying off, or through transport across cells (Camilleri, 2019). The review describes the popular picture, a barrier a single cell thick whose broken connections let chemicals, intact bacteria and food components into the bloodstream, as a popular perception, and it contrasts that with the layered barrier above.

So the honest one-line definition is this: intestinal permeability is a real, measurable property of the gut barrier that goes up in some conditions. “Leaky gut syndrome,” a named illness that supposedly drives a long list of unrelated symptoms, is a separate and much weaker claim.

Is leaky gut real?

Increased intestinal permeability is real; leaky gut syndrome as a stand-alone diagnosis is not established. The Camilleri review states there is “no controversy” about barrier dysfunction in diseases that inflame or damage the gut, naming celiac disease, Crohn’s disease and NSAID ulceration, and it lists inflammatory bowel disease, first-degree relatives of IBD patients, celiac disease, gut infections and HIV among conditions with documented barrier changes (Camilleri, 2019).

Where the evidence runs out is the jump from “permeability is measurably higher in these diseases” to “a leaky gut is the hidden cause of your fatigue, mood, skin or joint problems.” The same review lists conditions that have been linked to leaky gut “based on limited or no supporting data,” including autism, depression, fibromyalgia, chronic fatigue syndrome and others, and it says the popular claims appear “informed mostly by folklore or overreaching conclusions based on limited data” (Camilleri, 2019). It also lays out the case against over-reading permeability results: a leaky barrier can be a side effect of inflammation rather than its cause, and there is “no convincing evidence” that restoring the barrier changes the course of a disease in humans.

The most interesting evidence that permeability can come first is in Crohn’s disease. A prospective study from the Crohn’s and Colitis Canada GEM Project measured permeability in 1,420 asymptomatic first-degree relatives of people with Crohn’s, aged 6 to 35, and followed them for a median of 7.8 years; 50 developed the disease, and an abnormal baseline lactulose-to-mannitol ratio was associated with roughly three times the risk (hazard ratio 3.03) (Turpin et al., 2020). That is a real signal, but it is about risk in a genetically predisposed group, not proof that a leaky gut causes everyday symptoms in everyone else.

What causes leaky gut?

The best-documented causes of increased intestinal permeability are gut diseases and specific “stressors” on the barrier, not a vague imbalance. In humans, the Camilleri review groups them roughly like this (Camilleri, 2019):

• Inflammatory and ulcerating gut disease. Crohn’s disease, ulcerative colitis, celiac disease and gut infections all raise permeability, because an inflamed or damaged lining is a weaker barrier.
• NSAIDs. Anti-inflammatory painkillers such as indomethacin and aspirin raised permeability markers in human studies, and NSAIDs can cause small-bowel ulcers and inflammation.
• Endurance exercise. Hard cycling and running challenges raised permeability and markers of gut-lining damage, with one running study linking the rise to core body temperature.
• Pregnancy, surfactants and some dietary components. The review lists pregnancy, bile acids and food emulsifiers among factors that increase permeability.
• Irritable bowel syndrome, in a subset. A 2021 systematic review of 66 studies found barrier dysfunction in a “significant proportion” of adult IBS studies and in all four pediatric studies, most clearly in diarrhea-predominant and post-infectious IBS (Hanning et al., 2021).

The review also notes that permeability is influenced by the circadian cycle and by stress, factors that published studies do not always account for. What is missing from this list is just as telling: the common online causes, such as “toxins,” candida overgrowth or a single trigger food, are not what the human permeability literature is built on.

What does leaky gut feel like?

Increased intestinal permeability does not have a signature feeling of its own; the symptoms people notice usually come from whatever condition is raising it. In IBS, the 2021 systematic review found barrier dysfunction was linked to abdominal pain in 9 of 13 studies and to bowel changes in 6 of 9, but to overall symptom severity in only 1 of 6 (Hanning et al., 2021). In celiac or Crohn’s disease, the symptoms are those of the disease itself, which need a proper medical workup rather than a leaky gut label.

The checklists that circulate online (bloating, brain fog, fatigue, food sensitivities, headaches, skin flares) describe symptoms with many possible causes. The Camilleri review quotes one such checklist and notes that attributing food intolerance, fibromyalgia, chronic fatigue syndrome and autism to a leaky barrier is “unsupported by any data” (Camilleri, 2019). If you recognize yourself in one of those lists, the useful takeaway is that the symptoms are worth investigating, not that the cause has been found.

How is leaky gut diagnosed?

There is no validated clinical test that diagnoses “leaky gut,” and that is the single most important fact about the tests sold for it. The Camilleri review concludes there are “no validated clinical diagnostic tests,” that no gold standard exists, and that different methods “actually measure very different endpoints” (Camilleri, 2019).

The main research methods are:

• Sugar absorption tests. You drink non-metabolized sugars such as lactulose and mannitol, and the ratio excreted in urine over set time windows estimates small-bowel or colon permeability. The review points out that the old assumption that the two sugars cross the lining by different routes looks shaky, which complicates how the ratio is read, and that background intake of some sugars can skew results.
• Biopsy studies. Gut tissue taken at endoscopy is tested in the lab for how easily probe molecules pass, or for its tight-junction proteins. The review notes that biopsied tissue loses the nerve inputs that help regulate the barrier in the body.
• Endoscopic techniques. Confocal endomicroscopy and mucosal impedance measure barrier changes during an endoscopy.

Then there is zonulin, a blood marker widely used as a measure of intestinal permeability. A 2018 study found that a widely used commercial zonulin ELISA kit did not detect pre-haptoglobin 2, the protein zonulin was identified as, and instead picked up other proteins, most likely properdin (Scheffler et al., 2018). In plain terms, a “high zonulin” result from that kind of kit may not be measuring what the label implies. Our leaky gut tests explainer walks through what each at-home test actually measures.

How do you heal or fix leaky gut? What has actually helped

The approach with the strongest evidence is to treat the condition that is damaging the barrier; a handful of nutrients have changed permeability in small human trials, but none is an established leaky gut treatment. The Camilleri review is direct about the limit: whereas inflammatory or ulcerating diseases cause a leaky gut, “no such disease can be cured by simply normalizing intestinal barrier function,” and there are “no validated drug treatments yet” aimed at the barrier itself (Camilleri, 2019). It does note that anti-TNF therapy, which reduces gut inflammation in IBD, also restores permeability, which shows what treating the cause looks like in practice.

The best single trial is for glutamine in a narrow group. In a randomized, double-blind, placebo-controlled 8-week trial, completed by 106 adults who had developed diarrhea-predominant IBS after a gut infection and had measurably increased permeability, 43 of 54 on glutamine (79.6%) reached the main symptom endpoint versus 3 of 52 on placebo (5.8%), and elevated lactulose-to-mannitol ratios normalized in the glutamine group but not the placebo group, with similar adverse-event rates in both arms (Zhou et al., 2019). That is a meaningful result, but it applies to post-infectious IBS-D with confirmed hyperpermeability, not to anyone who suspects a leaky gut.

Beyond that, the evidence is small and scattered. The Camilleri review tabulates human studies where zinc carnosine reduced NSAID-induced permeability, a probiotic and prebiotic combination reduced aspirin-induced colon permeability, and inulin-enriched pasta, extra dietary fiber and colostrum shifted permeability markers, while psyllium had no effect in children with IBS. It calls most of these studies “small” and in need of replication, and says the probiotic evidence is “sparse” and often based on animal models (Camilleri, 2019). For the wider fiber trend, see what the fiber studies show about fibermaxxing.

Practically, the evidence supports a short, unglamorous list: get symptoms such as diarrhea, pain, bleeding or weight loss assessed so celiac disease, IBD or infection are not missed; review regular NSAID use with a clinician; and treat diagnosed conditions properly. Because the Camilleri review found no convincing evidence that restoring the barrier changes the course of disease in humans, supplement stacks and protocols built around a leaky gut diagnosis rest on an unproven premise.

Evidence at a glance

What has been shown to change intestinal permeability in people, and how strong the evidence is, based on the sources linked on this page (checked October 2026).

Attribute	Evidence level	What was shown	Who it applies to
Treating the underlying disease (for example anti-TNF in IBD)	Reported in IBD patients (Camilleri review)	Reduces inflammation and restores permeability	People with diagnosed IBD
Oral glutamine	One randomized controlled trial	Normalized permeability and improved symptoms over 8 weeks	Post-infectious IBS-D with confirmed hyperpermeability
Zinc carnosine, prebiotics, fiber, colostrum	Small human studies, need replication	Shifted permeability markers in specific settings	Mostly NSAID, exercise or diet challenge studies
Probiotics	Sparse human evidence, much of it from animals	Some barrier effects reported	Not established for any leaky gut use
BPC-157	Animal and cell studies only	Barrier and healing effects in rodent and lab models	No human permeability study published
KPV	Cell and mouse studies	Anti-inflammatory effects in colitis models	Human evidence mostly anecdotal

How long does it take to heal leaky gut?

No study has established a healing timeline for “leaky gut,” because it is not a single condition with a single course. In the glutamine trial, permeability normalized within the 8-week treatment period in people with post-infectious IBS-D (Zhou et al., 2019), and the Camilleri review treats endurance exercise and similar “stress” states as examples of a transient leaky gut (Camilleri, 2019). When permeability is driven by celiac disease or IBD, the timeline is the timeline of treating that disease, which a gastroenterologist can speak to; any program promising a fixed number of weeks to “heal your gut” is selling a number the research does not provide. The same gap applies to short 3, 7 and 14 day programs, which we grade in our gut reset claims review.

Where do BPC-157 and other peptides fit in the leaky gut story?

BPC-157 is a peptide people on social media often mention for leaky gut, but its permeability evidence comes from animal and cell research, with no published human study of the gut barrier. A 2020 paper titled around BPC-157 “rescuing” NSAID damage by “stabilizing intestinal permeability” is a review article, co-authored by Predrag Sikiric of the University of Zagreb with Korean colleagues, that describes what it called the peptide’s potential actions against leaky gut after NSAIDs “for the first time” (Park et al., 2020). A 2025 review led by Sikiric’s Zagreb group cites that work as showing increased tight-junction protein (ZO-1) expression and transepithelial resistance, laboratory measures of barrier tightness (Sikiric et al., 2025).

Read those findings for what they are: preclinical signals, and both papers involve the same Zagreb researcher. A 2025 scoping review of BPC-157 by University of Utah authors reported that only three pilot studies have examined BPC-157 in humans, covering knee pain, interstitial cystitis and intravenous safety, none of them in the gut, and concluded that until well-designed clinical trials are done the peptide should be considered investigational and its use approached with caution (McGuire et al., 2025). For the rodent ulcer, colitis and surgical-healing studies behind the gut reputation, see our explainer on BPC-157 and gut health: what is actually being studied, and for the IBS and IBD angle specifically, BPC-157 for IBS and IBD: what the evidence shows.

The other peptides in the “peptides for leaky gut” conversation sit at the same evidence level or lower. KPV, a melanocortin-derived tripeptide from the tail of alpha-MSH, has anti-inflammatory data from human cell lines and mouse colitis models (Dalmasso et al., 2008), and a 2023 review of the melanocortin system in IBD says much of the available evidence “is, in fact, preclinical” (Gravina et al., 2023). We cover it in KPV and inflammation: what is being studied. If you are weighing a peptide against low-dose naltrexone, an off-label medicine with two small randomized trials (46 participants in total) in Crohn’s disease (Parker et al., 2018, Cochrane), our comparison of LDN vs peptides for inflammation sets the evidence side by side.

BPC-157 status: Not FDA-approved; sold by some telehealth providers as a compounded prescription. An FDA advisory committee reportedly voted in July 2026 to recommend allowing pharmacies to compound it; nothing has changed yet. What these status terms mean.

What are people saying about leaky gut and BPC-157?

On social media, gut-lining repair is one of the most common reasons people give for trying BPC-157, but the posts are personal accounts, not measurements. Our Community Insights summary for BPC-157 on this site analyzed 16 public posts on X from July 16 to 20, 2026, and its themes line up closely with the leaky gut conversation:

• Taking it for leaky gut. Several posters describe oral BPC-157 aimed at repairing the gut lining, sometimes as part of a wider routine for gut and stress issues. They do not agree on how much it helps.
• The stomach-origin rationale. People often justify the gut use by pointing to the peptide’s stated origin in a protective protein from gastric juice. That is a reason for interest, not evidence of a barrier effect in humans.

The summary describes these posts as anecdotal, and none of them is a permeability measurement before and after, which is what it would take to show a gut barrier changed. That gap, between how confidently the protocol is shared and how little has been measured, is the core of the leaky gut story.

The bottom line on leaky gut

Intestinal permeability is a real, measurable feature of the gut barrier, clearly raised in celiac disease, Crohn’s disease, NSAID injury, some IBS and after hard endurance exercise, and in Crohn’s relatives it has even been linked to later disease. The wellness version, a hidden syndrome behind most chronic symptoms that a home zonulin test can confirm and a supplement protocol can patch, is not supported by the human research. If gut symptoms are the problem, the evidence points toward finding and treating the specific cause, with a clinician who can rule out the conditions that genuinely damage the barrier. Our list of questions to ask your doctor about peptides helps if peptides come up in that conversation.

Educational information only, not medical advice. Every research statement on this page is sourced to the peer-reviewed literature linked above, checked October 12, 2026; the status line reflects the network status page as of the same date. This page is drafted with AI assistance and fact-checked against the cited primary sources before publication.