A diet low in fermentable oligo-, di-, mono-saccharides and polyols (low-FODMAP diet) reduces symptoms of irritable bowel syndrome (IBS), and patients with gas-related symptoms can significantly improve on the low-FODMAP diet. However, the abundance of Bifidobacterium species is lower in fecal samples from patients on this diet. Levels of bifidobacteria have an inverse association with abdominal pain, so it might be good to maintain their abundance in patients with IBS. Some nonabsorbable, fermentable meal products (prebiotics) that serve as substrates for colonic bacteria can produce a similar effect on gas-related symptoms.
To compare the effects of the low-FODMAP diet vs prebiotics, Jose-Walter Huaman et al performed a randomized, parallel, double-blind trial of patients with functional gut disorders who complained of flatulence. Forty-four patients (31 with irritable bowel syndrome and 13 with functional abdominal distension) were randomly assigned to groups and 40 patients completed the study.
Huaman et al compared the effects of a prebiotic supplement (2.8 g/d Bimuno containing 1.37 g beta-galactooligosaccharide) plus a placebo (Mediterranean-type diet (prebiotic group, n = 19) vs a placebo supplement (2.8 g xylose) plus a diet low in FODMAPs (low-FODMAP group, n = 21) for 4 weeks; patients were then followed for 2 weeks.
The primary outcome was effects on composition of the fecal microbiota, analyzed by 16S sequencing. Secondary outcomes were intestinal gas production, as an marker microbiota activity, and digestive symptoms.
After 4 weeks, the authors observed opposite effects on microbiota in each group—particularly in relation to the abundance of Bifidobacterium sequences (increase in the prebiotic group and decrease in the low-FODMAP group), and Bilophila wadsworthia (decrease in the prebiotic group and increase in the low-FODMAP group).
Both treatments induced different effects on microbiota, particularly with relation to the abundance of Bifidobacterium genus sequences (increased with prebiotic and decreased with LFD; P = .042), and Bilophila wadsworthia (decreased with prebiotic and increased with LFD; P = .050)
Although the decrease in symptoms persisted for 2 weeks after patients discontinued prebiotic supplementation, symptoms reappeared immediately after patients discontinued the low-FODMAP diet.
The low-FODMAP diet reduced gas production, which might have contributed to the improvement of gas-related symptoms. Beta-galactooligosaccharide is a substrate for colonic microbiota and initially increases intestinal gas production. However, continued administration of beta-galactooligosaccharide induced an adaptation of gut microbiota and progressive decrease in gas production back to preadministration levels by 7 to 10 days of treatment. Further studies are needed to detmeine whether the effects of B-GOS administration on symptoms and microbiota are product-specific or are common to other prebiotics.
The study is small, did not estimate long-term efficacy or determine whether the prebiotic effect was product-specific or generic. However, intermittent treatment with prebiotics might provide an advantage over dietary restrictions for patients with functional gut symptoms.