Leaky gut
Also called increased intestinal permeability, leaky gut syndrome.
Dr Chad OkayFounder, Suna Health3 min read. Updated .
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 about 32 square metres, roughly half a badminton court (Helander & Fändriks 2014; the 'tennis court' figure widely cited in textbooks is a long-standing overestimate). 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, which normalises in a subgroup of people on a gluten-free diet.
- Inflammatory bowel disease (Crohn's, ulcerative colitis) involves measurably loosened tight junctions.
- Severe acute illness such as sepsis and major surgery is associated with abrupt loss of gut barrier function.
- Heavy alcohol use raises permeability acutely.
- Some non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen increase permeability acutely.
- 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, which supports overall gut health.
- 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, particularly critical illness, glutamine has some evidence for supporting gut barrier function, though reviews note clinical evidence remains limited. 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 doctor 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
- Surface area of the digestive tract, revisited (Helander & Fändriks 2014) (Scand J Gastroenterol (PMID 24694282))
- Intestinal permeability - a new target for disease prevention and therapy (Bischoff et al. 2014) (BMC Gastroenterol (PMC4253991))
- Zonulin, regulation of tight junctions, and autoimmune diseases (Fasano 2012) (Ann N Y Acad Sci (PMC3384703 / PMID 22731712))
- Antibody testing, permeability testing and zonulin vs small-bowel biopsy in coeliac patients on a gluten-free diet (Duerksen et al. 2010) (Dig Dis Sci (PMID 19399613))
- Psychological stress and CRH increase intestinal permeability in humans by a mast cell-dependent mechanism (Vanuytsel et al. 2014) (Gut (PMID 24153250))
- Severe, short-term sleep restriction does not alter intestinal permeability in healthy young men (2023) (Scientific Reports (PMC9816096))
- Aggravation of exercise-induced intestinal injury by ibuprofen in athletes (Van Wijck et al. 2012) (Med Sci Sports Exerc (PMID 22776871))
- Glutamine and the regulation of intestinal permeability: from bench to bedside (Achamrah et al. 2017) (Curr Opin Clin Nutr Metab Care (PMID 27749689))
- Coeliac disease (NHS)