What are the Causes of Irritable Bowel Syndrome (IBS)?
The causes of IBS are not well understood. Current and emerging research suggests bacterial imbalances in the intestine, infection, genetics, altered nutrient absorption and metabolism, brain-gut signaling, hypersensitivity, inflammation, GI motility, and psychological state may all play a role in the emergence of symptoms in patients.1
Changes in diet have been shown to alter the bacterial content of the intestines, also known as microbiota.2 By feeding bacteria with their diet, a patient increases and stabilizes bacterial numbers in the intestine. Changes in the microbiota in IBS-D patients can also occur with infection, known as bacterial gastroenteritis.3 These changes in bacterial populations can be long lasting and are directly associated with the onset of chronic symptoms in IBS-D.
There is evidence that changes in microbiota due to post-infectious IBS-D can effect levels and response to serotonin (provides feelings of well-being and affects motility) which are associated with abdominal discomfort, brain-gut signaling, hypersensitivity, and diarrhea.4-6 Interestingly, mutations in genes involved in the production of metabolites from tryptophan, the starting material to make serotonin, are particularly associated with IBS-D.7 Altered tryptophan metabolism in IBS-D patients leads to the production of chemical agents released from the intestinal mucosa into circulation that change the psychological state in IBS-D patients.8,9 Indeed, changes in microbiota can also effect tryptophan metabolism altering mood and psychological state.10 Finally, there are gene mutations that effect the synthesis, metabolism, and reabsorption of bile acids that alter motility.11