Exercise-Induced Gastrointestinal Syndrome (EIGS)
Systematic review
Key Findings
EIGS = disturbances of GI integrity and function that are common features of strenuous exercise
As exercise intensity and duration increase, there is considerable evidence for rises in intestinal injury, permeability and endotoxaemia, together with impaired gastric emptying, slowed small-intestinal transit and malabsorption
Heat stress and running mode appear to exacerbate these markers
Exercise of ≥2 hours at 60% VO2max appears to be the threshold at which significant GI perturbations manifest, irrespective of fitness status
GI symptoms (upper and lower tract) are common and a limiting factor in prolonged strenuous exercise
Strenuous exercise has a major but REVERSIBLE impact on GI integrity and function in healthy people; safety of strenuous exercise in chronic GI disease is not established
Full text; not checked against the abstract: the two primary pathways the review describes — circulatory-GI (splanchnic hypoperfusion → epithelial ischaemia → permeability → endotoxaemia) and neuroendocrine-GI (sympathetic drive → reduced motility and absorption)
Practical Application
Systematic review: markers of intestinal injury, permeability and endotoxaemia, and impaired gastric emptying, transit and absorption, rise with exercise intensity and duration; ≥2 h at 60% VO2max is the threshold at which significant GI perturbation appears regardless of fitness, and heat and running make it worse — the changes are reversible in healthy people. For a long ride or run in the heat, GI trouble is the expected physiology, not a personal weakness.
"Gut training" (REF-008): gradually accustom the gut to the carbohydrate doses you will race on
Not from this paper: a low-FODMAP diet before racing is supported for GI-symptom relief in the ISSN ultra-marathon position stand REF-528; the timing window is the base's own practice, not a finding here
Manage hydration and heat — heat stress exacerbates the markers of GI disturbance in this review
Not from this paper; the base's own practice: avoid NSAIDs before and during long events, and prefer isotonic, multiple-transportable carbohydrate solutions (REF-527) over hyperosmolar ones
Limitations
A systematic review of GI-integrity/function markers — not all clinical outcomes; no pooled effect sizes
Individual variability in GI sensitivity is enormous
The causal chain "permeability → symptoms → DNF" is not fully established
How this entry was checked and changed
Why this level
regraded 2026-09-27 from A: systematic review without pooling of mostly small acute-exercise studies
Content correction 2026-09-27
Added the abstract's central results that were missing: ≥2 h at 60% VO2max threshold irrespective of fitness, heat and running mode exacerbate, effects reversible; lead bullet now carries them.
"NSAIDs worsen permeability — REF-508" -> REF-508 is about drugs and mitochondrial adaptation, not GI permeability; NSAID and hyperosmolar-drink advice relabelled as the base's own practice. "Low-FODMAP 24-48 h out" -> the timing is not in this abstract; pointed to REF-528 (ISSN) for the low-FODMAP support.
Two-pathway model labelled as full-text content. Level A -> A- per KB-LEVEL-RUBRIC (SR without pooling). Sport adds "general".