Gut Barrier Integrity

The intestinal barrier is a single layer of epithelial cells sealed by tight junction proteins, covered by mucus and patrolled by immune tissue. Permeability is dynamic and regulated, not a fixed wall, and modest transient increases are normal after exercise or a large meal. Measurably increased permeability is well documented in coeliac disease, inflammatory bowel disease, cirrhosis and critical illness, where bacterial products crossing into circulation drive inflammatory responses. The contested territory is whether milder permeability changes cause the diffuse symptoms attributed to "leaky gut" in otherwise healthy people. The mainstream position is that increased permeability is usually a consequence of intestinal disease rather than a cause of systemic illness. What is not contested is that short-chain fatty acids, particularly butyrate from bacterial fermentation of fibre, are the primary fuel for colonocytes and support mucus production and tight junction expression.

Feed the barrier rather than patching it. Aim for 30 g or more of daily fibre from diverse plant sources, since bacterial fermentation produces the butyrate that colonocytes use as their main fuel and that upregulates tight junction proteins. Add fermented foods: a Stanford trial found increasing fermented food intake reduced inflammatory markers and increased microbial diversity more effectively than a high-fibre diet alone. Treat any underlying disease first, since coeliac disease and inflammatory bowel disease are far more consequential than any supplement. Reduce excess alcohol and chronic NSAID use, both of which measurably increase permeability. Prioritise sleep, since deprivation raises intestinal permeability in controlled studies. Among supplements, glutamine at 5-10 g/day is the primary fuel for enterocytes and has trial support in burns, critical illness and post-exercise permeability; zinc deficiency impairs tight junctions and correction helps; and specific probiotic strains have modest evidence. Avoid heavy reliance on commercial gut repair blends that rest on zonulin testing.

• •30 g or more of daily fibre from diverse plant sources
• •Regular fermented foods such as yoghurt, kefir, kimchi and sauerkraut
• •Limiting alcohol, which acutely increases permeability
• •Minimising chronic NSAID use
• •Prioritising 7-9 hours of sleep
• •Managing chronic stress, which alters barrier function
• •Moderate rather than excessive endurance exercise