Higher colonic bacterial fermentation linked to irritable bowel symptoms

Last Updated: 2015-09-02

By Will Boggs MD

NEW YORK (Reuters Health) - Altered colonic bacterial fermentation is associated with symptoms and colon transit time in individuals with irritable bowel syndrome (IBS), researchers report.

"The interesting finding is that colonic fermentation (as measured by pH and to a certain extent by level of short-chain fatty acid (SCFA)) is higher in patients with IBS than in healthy controls," Dr. Yehuda Ringel from University of North Carolina, Chapel Hill, told Reuters Health by email. "This finding supports the idea that the intestinal microbiota has an important role in the pathogenesis of the disorder."

Altered intestinal fermentation may be associated with intraluminal excessive gas production and altered motility, features commonly observed in IBS, but its role in the pathogenesis of IBS remains uncertain.

Dr. Ringel's team investigated the location and magnitude of altered intestinal bacterial fermentation in IBS and its clinical subtypes and examined their relation to bowel characteristics and gastrointestinal symptoms in a study of 147 individuals, including 114 with IBS and 33 healthy controls.

Their results appear in The American Journal of Gastroenterology, online August 25.

"It is the first study where assessment of intra-luminal intestinal fermentation was done in vivo in humans, and we were able to measure the fermentation process in real time throughout the GI tract and assess and compare this process in different segments," Dr. Ringel said.

Mean total colonic pH levels were significantly lower in the IBS group than in the healthy controls (6.8 vs. 7.3, p=0.042). Lower pH is thought to reflect higher intraluminal bacterial fermentation.

Small bowel pH did not differ significantly between IBS patients and healthy controls, the researchers found.

Fecal short-chain fatty acids (SCFAs) are also thought to reflect intestinal bacterial fermentation, but levels of four SCFAs (acetate, propionate, butyrate, and lactate) did not differ significantly between IBS patients and healthy controls.

"Unlike what we expected, the colonic pH levels positively correlated with IBS symptom scores," the researchers note. "This finding suggests that other factors such as abnormal intestinal motility and psychological disturbances may be more important than bacterial fermentation in determining symptoms severity."

In contrast, fecal SCFA levels had no correlation with either symptom scores or quality-of-life scores.

"The most surprising finding is the lack of fermentation differences between patients with IBS and healthy controls in the small bowel," Dr. Ringel said. "This finding does not support SIBO (small intestinal bacterial overgrowth) as a pathological mechanism for IBS as has often been suggested."

"This study provides possible explanation for physicians to why many patients relate their symptoms to certain types of food, particularly carbohydrates, which serve as substrate for colonic bacterial fermentation," Dr. Ringel concluded. "Our study highlights the need for further investigation of the role of the human microbiota and its function in generating commonly reported functional GI symptoms."

SOURCE: http://bit.ly/1EBhevf

Am J Gastroenterol 2015.