Fecal microbiota transplantation has shown some ability to reduce symptoms of mild-to-moderate ulcerative colitis in controlled studies, but it is not currently advised for routine patient care...
Mechanism
Synthesis from 1 study
When the good bacteria in the gut are out of balance, they stop making chemicals that keep the gut lining strong and calm. This lets harmful bacterial parts leak through, triggering low-level inflammation that damages the lining and makes the gut overly sensitive, leading to diarrhea and pain. FMT...
Most probable mechanism
An imbalance in gut bacteria leads to a weakened intestinal lining, allowing bacterial parts to leak through and trigger low-grade inflammation. This inflammation damages the lining further, reduces protective chemicals, and causes the gut to become overly sensitive, which can lead to chronic diarrhea and tissue damage.
A shift in gut bacterial composition reduces the abundance of bacteria that produce short-chain fatty acids, particularly butyrate.
Lower levels of short-chain fatty acids impair the activation of immune sensors in the gut lining, reducing the production of protective molecules that maintain barrier integrity and calm inflammation.
Reduced short-chain fatty acids also decrease the expression of proteins that seal the gaps between gut lining cells, increasing leakage of bacterial components into underlying tissue.
Bacterial components such as lipopolysaccharide and flagellin cross the weakened barrier and bind to immune receptors on immune cells, triggering a cascade that produces inflammatory signals.
Persistent immune activation leads to low-grade inflammation without visible tissue destruction, which damages the lining further and increases sensitivity of nerve fibers in the gut wall.
Inflammation and barrier damage alter the metabolism of tryptophan, increasing production of compounds that overstimulate gut nerves and increase fluid secretion, contributing to diarrhea.
Less supported by current evidence, but not ruled out
After a prior gut infection, the immune system may mistakenly attack proteins that control gut movement, slowing down the clearing of bacteria and leading to overgrowth and irritation.
A prior bacterial infection triggers the immune system to produce antibodies against a bacterial toxin.
These antibodies cross-react with a similar human protein found in gut nerve and muscle cells.
This autoimmune attack damages cells that coordinate gut movement, causing slow transit and bacterial buildup.
Bacterial overgrowth increases production of irritants that worsen inflammation and diarrhea.
An imbalance in gut bacteria reduces the conversion of bile acids into forms that help calm inflammation, leaving the gut lining more vulnerable to damage.
Gut bacteria that normally modify bile acids become less abundant.
This causes a buildup of unmodified bile acids and a drop in modified forms that activate anti-inflammatory receptors.
Without activation of these receptors, the gut loses a key signal that normally suppresses inflammation and repairs the lining.
Evidence from Studies
Supporting (1)
Community contributions welcome
Gut Microbiota in Irritable Bowel Syndrome and Inflammatory Bowel Disease: Differences in Pathophysiology, Biomarkers, and Treatment Implications
Contradicting (0)
Community contributions welcome
Gold Standard Evidence Needed
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