Carb-related symptoms in IBS due to colon hypersensitivity to distention

Last Updated: 2016-10-28

By Will Boggs MD

NEW YORK (Reuters Health) - Carbohydrate-related symptoms in irritable bowel syndrome (IBS) result from colon hypersensitivity to distention, not from excessive gas production, researchers from the U.K. report.

"This paper provides evidence of how fermentable carbohydrates can distend the colon," Dr. Giles Major from the University of Nottingham told Reuters Health by email.

"It provides a mechanistic basis for the clinical observation that reducing such carbohydrates in the diet can reduce feelings of bloating and discomfort, but it also makes an important point: that, in this group at least, IBS patients did not have more gas in their colons - they got more discomfort from the same amount of gas as was found in others," he said.

Consumption of fermentable carbohydrates - termed fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) - has been associated with an exacerbation of symptoms in patients with IBS. Dietary changes reducing the consumption of those carbohydrates result in a reduction of symptoms, but the mechanism remains unclear, according to Dr. Major and colleagues.

The team conducted a three-period crossover study of 29 adult patients, examining changes in the Composite Symptom Score (CSS). The CSS includes four symptoms: gas/flatulence, bloating, pain/discomfort, and diarrhea, with each symptom scored on a scale from 0 (none) to 3 (severe/disabling).

One in five IBS patients (21%) experienced a significant increase in symptoms (change in CSS >=3) after the glucose control and 45% reached this threshold after inulin, a poorly absorbed carbohydrate. Fructose consumption increased symptoms significantly in 38% of IBS patients.

Volunteer response rates were lower for inulin (3/29) and fructose (3/29) but not significantly different for glucose (2/29), the researchers report in Gastroenterology, online October 13.

Although colonic volume and breath hydrogen in IBS patients were higher for both fructose and inulin than for glucose, the patterns of change were similar among volunteers.

Peak rise in colonic gas correlated with symptoms in patients after inulin, but there was no difference in this variable between patients who did and did not report symptoms.

For fructose, the only variable that differed significantly between those who reported symptoms and those who didn't was their initial somatization score (median, 8 in those with symptoms vs. 5 in those without, where less than 7 is normal).

"The study therefore offered no evidence that patients who reported symptoms produced more colonic gas than those who did not," the researchers conclude. "An alternative hypothesis would be that, as has been shown with lactose malabsorption, the patients with symptoms had a lower sensory threshold for reporting."

"Patients who report symptoms relating to fermentable carbohydrate may be accurately assigning the cause of their problems," Dr. Major said. "The same patients may also have visceral hypersensitivity. Treating with the two modalities of dietary modification and pharmacotherapy could help."

"An unknown quantity in our study is the role of the microbiota," Dr. Major added. "It may be that certain microbiomes induce more gas production. There may also be small molecule products of fermentation that mediate nerve signaling. The prospect of linking microbiome signatures to dietary sensitivity holds real promise tor personalized care of patients."

SOURCE: http://bit.ly/2fdPxSD

Gastroenterology 2016.