Gut anatomy and function

Leaky gut

Also called: increased intestinal permeability, leaky gut syndrome

Leaky gut is a popular term for increased intestinal permeability, where the lining of the gut becomes more porous than normal. The phenomenon is real and measurable in some conditions, including coeliac disease, IBD and severe stress states. Whether it causes a wider syndrome of symptoms in otherwise-healthy people is contested. Most NHS gastroenterologists treat the consumer version of leaky gut as unproven.

What the gut lining actually does

Your gut lining is one cell thick and covers an area roughly the size of a tennis court. The cells are sealed together by structures called tight junctions. The lining is not perfectly impermeable: it lets water, nutrients, and small molecules through, while keeping bacteria and undigested food on the gut side. The balance between sealing and selective permeability is dynamic and varies through the day.

Where the science is solid

  • Coeliac disease causes increased permeability that resolves on a gluten-free diet.
  • Inflammatory bowel disease (Crohn's, ulcerative colitis) involves measurably loosened tight junctions.
  • Severe burns, sepsis, and major surgery cause acute permeability increases.
  • Heavy alcohol use raises permeability acutely.
  • Some non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen increase permeability with regular use.
  • Zonulin, a protein that regulates tight junctions, is elevated in some autoimmune conditions, demonstrated in research by Alessio Fasano's group.

Where the science is contested

  • Whether mild permeability changes in otherwise-healthy people cause symptoms like fatigue, brain fog, joint pain, skin conditions and food sensitivities.
  • Whether commercial leaky-gut tests (lactulose-mannitol ratio, zonulin assays) accurately measure clinically meaningful permeability.
  • Whether specific supplements (glutamine, collagen, slippery elm, butyrate) reliably reduce permeability in healthy people.
  • Whether low-grade permeability is cause or consequence of conditions it tracks with.

What the NHS position is

The NHS does not recognise leaky gut syndrome as a standalone clinical diagnosis. Specific permeability changes in coeliac, IBD and other defined conditions are well accepted. The wider syndrome marketed by some functional medicine providers is not. NICE has not produced specific guidance for it. People with persistent gut symptoms are advised to follow the IBS or IBD diagnostic pathway rather than seek leaky-gut treatment.

What helps gut barrier function regardless

  • Diverse fibre intake to feed butyrate-producing bacteria.
  • Adequate sleep. Sleep deprivation increases permeability in studies.
  • Limiting alcohol to within UK guideline limits.
  • Limiting NSAID use to genuine need.
  • Managing chronic stress. Psychological stress raises permeability in lab studies.
  • Treating underlying conditions. Permeability often normalises when the underlying issue is addressed.

Common questions

Is leaky gut a real condition?
Increased intestinal permeability is real and measurable in defined clinical conditions. The wider consumer syndrome of leaky gut, with non-specific symptoms attributed to gut leakiness, is not accepted as a clinical diagnosis in the UK or by mainstream gastroenterology bodies.
Can supplements heal leaky gut?
Glutamine, collagen and slippery elm are the most marketed. Evidence in healthy adults is weak. In specific clinical settings, like critical illness or severe IBD, glutamine has some evidence for restoring gut barrier function. Generic consumer use is not evidence-based.
How would you actually test for leaky gut?
Research uses the lactulose-mannitol urinary ratio, blood zonulin levels, or imaging. Commercial home tests vary widely in quality. Specialist NHS gastroenterology can run validated tests if there is clinical suspicion of conditions like coeliac disease or IBD.
Should I worry about leaky gut?
If you have persistent gut symptoms, see a GP and follow the IBS or IBD diagnostic path. Avoid spending money on commercial leaky-gut tests or treatment programmes before that. The conditions that actually cause clinical permeability are well-recognised and treated through standard care.

Sources