Supplementing Fiber in a Low FODMAP Diet Improves Bowel Habits in IBS

Fiber supplementation while on the low fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) diet provides no additional symptom relief of irritable bowel syndrome (IBS) symptoms compared with the FODMAP diet alone but does increase stool output, according to study findings published in Clinical Gastroenterology and Hepatology.

While a low FODMAP diet can decrease gastrointestinal (GI) symptoms in IBS, it can also reduce overall fiber intake, which could potentially influence gut health. In this randomized, double-blind, crossover trial, researchers observed the effects of fiber supplementation with a low FODMAP diet on physiological markers in patients with IBS.

Of 45 patients assessed for eligibility, researchers enrolled 26 patients with IBS. All patients met the Rome IV criteria and averaged GI symptoms greater than 30 mm over a 5-day prescreening with a 100-mm visual analog scale (VAS), where 0 mm denoted no symptoms and 100 mm denoted the worst symptoms. Patients were randomly assigned to 3 different low FODMAP diets that varied by total fiber content: control (23 g/d), sugarcane bagasse (33 g/d), or a combination of sugarcane bagasse and resistant starch (45 g/d). All 3 diets lasted for 14 days and concluded with a washout period of at least 21 days, where patients resumed their normal diet.

Study participants had a median age of 34 (range, 18-61) years, 25 were women, and the median body mass index (BMI) was 22.8 (16.2-30.7) kg/m².

Patients were evaluated based on the IBS Severity Scoring System (IBS-SSS) and other questionnaires to document GI symptoms, food intake, and energy levels. Fecal samples were collected on days 3 through 7. Study participants were weighed on day 9, and stool output was collected on days 10 through 14.

The primary endpoint was the difference in stool output between the 3 diets.

After implementing the low FODMAP control diet, overall GI symptoms decreased from baseline by a median 51% per VAS (P <.001) and 39% per IBS-SSS (P =.003).

The sugarcane bagasse fiber-supplemented diet reduced overall GI symptoms by a median 34% per VAS (P <.001) and 44% per the IBS-SSS (P =.001). The combination diet reduced overall GI symptoms by a median 31% per VAS (P =.001) and 21% per the IBS-SSS (P =.021).

Diets supplemented with sugarcane bagasse resulted in approximately a 50% increase in stool output. Results were also consistent with the group taking the combined fiber supplementation (P <.001).

Study limitations include enrolling a disproportionately higher number of women, so findings may not be generalizable; patient-reported challenges adjusting to the new diets; and not meeting power calculations for the study.

“Concomitant supplementation of minimally fermented sugarcane bagasse, alone and in combination with slowly fermented RS [resistant starch], is well tolerated in patients with IBS with initiation of a low FODMAP diet and can enhance the base diet by increasing stool water content for patients with firm stool and hastening colonic transit … for patients with slow colonic transit,” the study authors wrote. “The changes in stool characteristics and motility were attributable to the minimally fermented fiber with additional supplementation of RS [resistant starch] having little impact.”