Intestinal permeability is a real, measurable property of the gut lining, and it genuinely changes in certain diseases. “Leaky gut syndrome”, meaning a standalone diagnosis that causes fatigue, autoimmunity, skin conditions, mood disorders and weight gain, and that is fixed by a supplement protocol, is not established. Both statements are true at once, and the space between them is where a great deal of money changes hands.
What is actually established
Your intestinal lining is one cell thick, and the cells are joined by structures called tight junctions. They are supposed to let nutrients through while keeping bacteria and partially digested food out. That barrier is dynamic, not fixed, and it can become more permeable.
Increased permeability is well documented in specific conditions: celiac disease, Crohn’s disease and ulcerative colitis, some gastrointestinal infections, and critical illness. Certain exposures increase it too, including NSAIDs such as ibuprofen, heavy alcohol use, and chemotherapy or radiation.
So the phenomenon is not fringe. It is in the literature and it matters clinically in those settings.
What is not established
That permeability causes the long list of conditions attributed to it. In the diseases where increased permeability is documented, the direction of causation is largely unresolved. In celiac disease, for example, the intestinal damage and the permeability travel together, and permeability improving when gluten is removed is entirely consistent with it being a consequence rather than the root cause.
Being a marker of intestinal disease is not the same as being the engine of unrelated systemic disease, and most of the claims made for “leaky gut” quietly make that leap.
That the tests sold direct to consumers are informative. Zonulin, the marker most often marketed, has had serious questions raised about what commercial assays are actually measuring. Lactulose-mannitol testing is a legitimate research tool that has not translated into a validated clinical test with an actionable result.
That specific supplements “seal” the gut. Glutamine, collagen, bone broth, aloe and the rest are sold on this premise. Some may have modest effects in specific clinical situations. None has established that it repairs a barrier and thereby resolves systemic disease, which is the claim being made when you are sold a protocol.
Why the idea is so attractive
Because it explains everything, and because it arrives with a plan. Someone with fatigue, joint aches, bloating, brain fog and a rash has usually been to several appointments and received several unrelated non-answers. One mechanism that ties the whole picture together, plus a protocol, is enormously appealing.
The problem is not that patients are gullible. It is that a unifying story is more satisfying than “we need to test several things and some will come back normal”, even when the second is the honest position.
What to do instead, which is not nothing
Test for the diagnosable things. Celiac disease, which must be tested while you are still eating gluten. Inflammatory bowel disease, where calprotectin is a genuinely validated marker. Pancreatic insufficiency. Thyroid disease. Iron deficiency. These are real diagnoses with real treatments, and they account for a substantial share of people who arrive convinced they have a leaky gut.
Remove what is known to increase permeability. Regular NSAID use and heavy alcohol are the two with the clearest evidence, and both are actionable this week.
Feed the barrier the boring way. A diet with genuine plant diversity and adequate fibre supports the microbiome and the gut lining, with better evidence behind it than any supplement marketed for the purpose. Sleep and physical activity belong on the list too, unglamorously.
Treat symptoms as worth investigating rather than worth explaining. If bloating is the issue, it has a specific differential. Bloating that will not go away walks through it, and what a GI-MAP test actually shows covers which stool markers are worth acting on and which are not.
Where we stand
Functional medicine done well means taking unexplained symptoms seriously and investigating them thoroughly. It does not mean adopting every mechanism that sounds plausible. We will test what is testable, treat what is treatable, and tell you plainly when the evidence for something does not support the confidence with which it is usually sold.
Gut health and functional medicine here starts with a full hour and a real history, because that is what sorting this out takes.
Consults are available in person at our Deerfield Beach clinic and by telehealth anywhere in Florida.
Medically reviewed by Krishna Borges, MSN, APRN, FNP-C. This article is for general education and is not a substitute for individual medical advice.