#142 The Low FODMAP Diet: Food for thought or just an irritable idea?

CLINICAL QUESTION

Does the low FODMAP diet improve symptoms for patients with irritable bowel syndrome?

BOTTOM LINE

A low FODMAP diet may improve symptoms for patients with primarily diarrhea subtype irritable bowel syndrome (IBS). However, most studies were low quality (small numbers and short duration), and therefore more high quality studies are needed.

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EVIDENCE

Four meta-analyses^1-4 (4-8 randomized controlled trials, 293-596 participants, ROME II/III entry criteria), mainly young females. Compared with control, low FODMAP diet improved:

Symptoms of abdominal pain^1-3 and bloating^1-2
Quality of life - small to moderate effect³
Global IBS symptoms⁴: 28% had ongoing symptoms vs 59% control, NNT 4
Severity of symptoms²
Limitations: short follow-up (range: 10 days – 3months); small number of trials. Poor use of statistics (eg. odds ratios (without event rates) and/or standard mean differences) limit clinical interpretation of data.

A systematic review assessed the quality of RCTs of LFD for IBS (9 trials, 542 patients) and found all trials were at high risk of bias, often due to lack of blinding and choice of control group;⁵ Example of actual symptom changes: Largest, high-quality, 6-week, open-label RCT of 123 Danish IBS patients, under specialist care.⁶

500-point symptom scale (minimal clinically important difference=50):⁷
- Low FODMAP diet improved ~150 points, probiotic ~80, normal diet ~30 points.
Sub-group analysis: Only diarrhea patients improved.
Limitations: Pre-enrollment investigations: colonoscopy, genetic lactase deficiency testing; per-protocol analysis.

Context:

Cohort studies demonstrate LFD benefit^2,8 but IBS patients have high placebo response rate⁹ (even when told getting placebo).¹⁰
IBS guidelines suggest offering patients a “low Fodmap diet trial.”^11,12 Adherence to the diet¹³is approximately 40%.
Patients who initially improve on LFD, worsen with reintroduction of fructose or fructans.¹⁴
Low FODMAP diet is restrictive, limiting many fruits, dairy products, wheat, legumes, and artificial sweeteners.¹⁵ Examples available online.¹⁵