Hormonal
Intense exercise (above 60% VO2max) causes gastrointestinal hyperpermeability ('leaky gut') and endotoxemia by reducing splanchnic blood flow and increasing stress hormones, which can be mitigated by microbiota-derived Short Chain Fatty Acids (SCFAs) that strengthen the intestinal barrier.
When you train hard (>60% max effort), your body diverts blood away from your gut, causing 'leaky gut' and allowing toxins (LPS) into your bloodstream, which causes inflammation and fatigue. You can't always avoid this stress, but you can strengthen your gut barrier. Consume prebiotics and probiotics to boost Short Chain Fatty Acids (like butyrate), which act as fuel for gut cells and tighten the intestinal barrier, helping you handle intense training with less systemic inflammation.
Intense exercise over a prolonged period of time increase stress hormones and lipopolysaccharides (LPS) translocation in the gastrointestinal tract, which triggers immune responses that often results in increased pro-inflammatory cytokines and intestinal permeability.
Why this rating
Supported by multiple human studies cited (marathon runners, triathletes) showing increased LPS and GI symptoms, alongside mechanistic animal data.
Source
Exercise-induced stress behavior, gut-microbiota-brain axis and diet: a systematic review for athletes
Allison Clark et al. · Journal of the International Society of Sports Nutrition · 2016
DOI 10.1186/s12970-016-0155-6
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