A fibre supplement on a low-FODMAP diet changed the microbiota without worsening IBS

Design

Randomised, double-blind, placebo-controlled pilot trial

Population

26 adults with IBS following a low-FODMAP diet, Australia

Primary outcome

Gut microbiota, symptoms and gut health measures over 3 weeks

Effect

Symptoms stable; Ruminococcus 5.5-fold rise; lower GI-specific anxiety (p=0.01)

A low-FODMAP diet eases IBS symptoms but may reduce beneficial gut bacteria. This Australian pilot trial randomised 26 adults with IBS on a low-FODMAP diet to a commercial fibre blend or placebo for three weeks, double blind.

Gut symptoms and sleep stayed stable in both groups. The fibre group ate more resistant starch, showed shifts in genus-level microbiota, including a 5.5-fold rise in Ruminococcus, and reported less gastrointestinal-specific anxiety. Faecal and blood biomarkers did not change.

This is a very small, short pilot, and microbiome changes are a surrogate. The practical point is modest: fibre adapted to a low-FODMAP diet may not worsen symptoms.

• Use the low-FODMAP diet in phases, with reintroduction, rather than indefinitely.
• Involve a dietitian to maintain fibre intake during restriction.
• Consider low-FODMAP fibre sources for patients who need to stay restricted.
• Do not recommend a specific commercial supplement on this evidence.

Why it matters

It addresses a known downside of the most effective dietary treatment for IBS.

Don't overread it

A 26-patient, three-week pilot; the microbiome changes are surrogate outcomes.

The statistics, in plain English

With 13 patients per group over three weeks, the trial cannot show clinical benefit. Microbiota shifts do not necessarily translate into better symptoms.

Read the rest in the app

You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.

Get Daily Doctor — free

Scan to keep reading on your phone. No account needed to start.