Traditionally, the diet low in fermentable oligo-, di-, and monosaccharide and polyol (FODMAP) – best as a 2-phased intervention, with strict reduction of all slowly absorbed or indigestible carbohydrates (i.e., FODMAPs) followed by reintroduction of some of them according to tolerance – has been widely used for overall gastrointestinal symptom relief in patients with irritable bowel syndrome (IBS). However, decreasing intake of fermentable carbohydrates reduces available fuel for the gut microbiota, subsequently altering bacterial composition in the colon.

Although it has been shown that incorporating fermentable carbohydrates may increase the severity of IBS symptoms (pain, bloating) due to gas production from fermentation, they may also help manage other symptoms of IBS (constipation, diarrhea) through impact on the gut microbiota. While these prebiotic fibres have varying effects on IBS symptoms, little is known about the impact specific types and doses of prebiotics have in IBS management. Dr. Fernando Azpiroz and his team from the Vall d’Hebron Research Institute in Barcelona (Spain) set out to clarify whether certain prebiotics help or hinder IBS symptoms and evaluate their utility in maintaining the gut microbiota, when compared to the low-FODMAP diet.

The researchers compared the effects of a low-FODMAP diet plus a placebo supplement (low-FODMAP group, n=21) versus a prebiotic supplement (galacto-oligosaccharides) plus a Mediterranean-type (prebiotic group, n=19) diet for 4 weeks on the gut microbiota composition and gas production. The gut microbiota was analyzed prior to and at the end of intervention, as well as 2 weeks following discontinuation of the intervention.

As expected, the low-FODMAP diet improved IBS symptoms (such as pain, distension, bloating, and flatulence), but decreased Bifidobacteria, in line with previous studies. Bifidobacteria increased 2 weeks following discontinuation of the low FODMAP diet, showing this change was transient.  The participants on the low-FODMAP diet had an increase in Bilophila wadsworthia, a bacterium implicated in excess gas and intestinal inflammation. This increase persisted for 2 weeks following discontinuation of the low-FODMAP diet and was correlated with an increase in bloating frequency after intervention.

These findings show that changes in the gut microbiota composition driven by a low-FODMAP diet may persist after 2 weeks of stopping the diet and may perpetuate IBS symptoms, such as bloating. Interestingly, the prebiotic group had a similar reduction in symptoms of pain, distension, and bloating by the end of the 4-week intervention, but with an increase in Bifidobacterium as well as a decrease in Bilophila wadsworthia, that persisted 2 weeks after discontinuation of the prebiotic.

Initially, the prebiotic group reported an increase in flatulence, which resolved as the gut microbiota adapted to the substrate. This returned to baseline after 7-10 days of adjusting to the supplement – however it was not improved as was with the low FODMAP diet.  Remarkably, 2 weeks following discontinuation of the intervention, symptom improvement was maintained in the prebiotic group, but not in the low-FODMAP group. This suggests that positive symptom changes were likely attributable to changes in the gut microbiota.

This study highlights the role of prebiotic fibers in ameliorating IBS symptoms through changes in the gut microbiota composition. Future research looking at how long microbial changes are sustained post-treatment for IBS would help in understanding how to best use prebiotic fibers in functional gastrointestinal disorders.



Huaman JW, Mego M, Manichanh C, et al. Effects of prebiotics vs a diet low in FODMAPS in patients with functional gut disorder. Gastroenterology. 2018; doi: 10.1053/j.gastro.2018.06.045.