“Leaky gut” is a phrase doing two jobs at once, which is why the conversation around it is such a mess. One job is describing a real, measurable phenomenon. The other is selling powders.
What is actually evidenced
Evidence: Strong that intestinal permeability exists and varies. Your gut lining is selectively permeable by design — that is how nutrients get in. The tight junctions between cells regulate what passes.
That regulation can be altered. Alcohol, certain medications including regular NSAID use, acute infection, coeliac disease and inflammatory bowel disease all measurably increase permeability. None of this is controversial.
What has been extrapolated
Evidence: Weak for the popular version. The leap from “permeability changes exist” to “permeability is the root cause of your fatigue, brain fog, joint pain, anxiety and skin” is considerably longer than the data supports.
In many conditions where raised permeability is observed, it is unclear whether it is a cause or a consequence of the inflammation already present. That distinction matters enormously and is almost always skipped.
When a mechanism is real but the causal claim is not, that gap is exactly where products get sold.
The supplements sold on this
L-glutamine. Genuinely important for intestinal cells and reasonably evidenced in specific clinical settings such as burns and critical illness. Evidence in otherwise healthy people with vague symptoms is thin.
Collagen and bone broth. Popular, pleasant, and lacking human trial evidence for repairing intestinal permeability specifically.
Zinc carnosine. Has some supporting data for gastric protection. Reasonable, not transformative.
None of these are dangerous. They are simply being sold with more confidence than the evidence carries, and often at a price that would buy a great deal of vegetables.
What I would do instead
The interventions with the strongest evidence for gut lining health are unglamorous and free: plant diversity, adequate fibre, sleep, lower alcohol, fewer unnecessary NSAIDs, and managing chronic stress.
You would do all of those anyway. That is rather the point — and it is why nobody markets them.
Questions people actually ask
Is leaky gut a real diagnosis?
Increased intestinal permeability is a real, measurable finding. “Leaky gut syndrome” as a standalone diagnosis explaining a wide range of symptoms is not recognised clinically.
Should I get a permeability test?
The commercially available tests are not well validated for guiding treatment, and a result will not change the sensible first steps. I would spend the money on food.
Does PCOS cause it?
Some studies have found markers of increased permeability in women with PCOS, likely tied to the lower microbial diversity and higher inflammatory markers seen in the condition. The direction of causation is not established.
More in the gut health section.