Treatment efficacy of a low FODMAP diet compared to a low lactose diet in IBS patients: A randomized, cross-over designed study

Clin Nutr ESPEN. 2020 Dec;40:83-89. doi: 10.1016/j.clnesp.2020.09.020. Epub 2020 Oct 6.


Background and objective: A low FODMAP diet (LFD) has become a standard treatment in irritable bowel syndrome (IBS) patients. Compliant adherence to a LFD is challenging. We investigated the effect of a LFD compared to a less restrictive low lactose diet (LLD) in a randomized cross-over trial with IBS patients.

Methods: Twenty-nine IBS patients were randomly assigned to two groups. After a run-in phase of 14 days, patients received 21 days of either a LFD or LLD. This intervention was followed by a washout period of 21 days before crossing over to the alternate diet. Dietician led diet instruction was given continuously. An IBS Severity Scoring System (IBS-SSS) was filled in at the end of each study period. To enhance study adherence, daily symptoms were assessed using a Visual Analog Scale (VAS).

Results: IBS patients, irrespective of lactase deficiency, had a significantly reduced IBS-SSS score after both diets (LFD p = 0.002, LLD p = 0.007) without significant difference. On both diets, patients reported that IBS had less impact on their daily life compared to the time before the study (p < 0.01). On daily assessment, IBS patients on LFD reported significantly less abdominal pain (median VAS difference to baseline -0.8 (-2.8 to 2.7, p = 0.03) and less bloating (-0.5 (-4.1 to 3.4, p = 0.02) than patients on the LLD.

Conclusion: Both diets improved the overall IBS severity significantly and patients' preference of the two diets was similar. LFD but not LLD effectively reduced pain and bloating in patients with IBS.

Keywords: IBS; IBS symptom severity score; Lactose intolerance; Low FODMAP diet; Low lactose diet.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cross-Over Studies
  • Diet, Carbohydrate-Restricted*
  • Disaccharides
  • Fermentation
  • Humans
  • Irritable Bowel Syndrome*
  • Lactose*
  • Monosaccharides
  • Quality of Life
  • Treatment Outcome


  • Disaccharides
  • Monosaccharides
  • Lactose