A diet low in FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) has been studied mostly in the context of irritable bowel syndrome (IBS) and is known to reduce functional gastrointestinal symptoms in this population. In addition, altering FODMAP intake appears to impact fecal microbiota composition in both healthy individuals and those with IBS.

The observed success of the low-FODMAP diet in reducing gastrointestinal (GI) symptoms in IBS made a group of researchers ask whether the diet could also address functional GI symptoms in those with inflammatory bowel diseases (IBDs) such as Crohn’s disease. This idea was explored in a recent study from the group at Monash University (Australia) that originally developed and tested the low-FODMAP diet.

In this cross-over trial, researchers first tracked the habitual diets of a small group of nine patients with inactive Crohn’s disease. Next, each participant was randomized to 21 days of a provided experimental diet: either (1) low-FODMAP or (2) typical “Australian”. After a washout period of his or her habitual diet for at least 21 days (until GI symptoms had returned to baseline), each participant consumed the other experimental diet for an additional 21 days.

The low-FODMAP diet in the study included acceptable foods like bananas and citrus fruits, as well as meals and desserts prepared with sugar but without honey or sweeteners. In contrast, the typical Australian diet contained common high-FODMAP foods like apples and watermelon as well as wheat. Both diets contained gluten, and both included lactose-free yogurt and milk. The researchers took care to match the two interventional diets for energy, macronutrients, sugars, starch, and fibre. Because the low-FODMAP diet was naturally lower in total fibre and resistant starch, it was supplemented with small quantities of psyllium and resistant starch.

The participants’ habitual diets were found to be somewhat higher in FODMAPs than the interventional low-FODMAP diet. Starch intake was also higher in participants’ habitual diets than in both tested diets.

In the study, participants’ GI symptoms were recorded daily, and stool samples were collected at the end of each diet. Samples were analyzed for calprotectin (a measure of intestinal disease activity), pH, short-chain fatty acids (SCFAs), and bacterial abundance.

Differences in fecal microbiota were observed between the low-FODMAP and the Australian diets: across all participants, the Australian diet increased the relative abundance of butyrate-producing Clostridium cluster XIVa and mucus-associated Akkermansia muciniphila, while it decreased Ruminococcus torques, relative to the low-FODMAP diet.  No significant differences were observed in the fecal microbiota profiles when participants consumed their habitual diets compared to the low-FODMAP diet. Total bacterial abundance was similar for the two interventional diets and the habitual diets.

Participants’ GI symptoms doubled in severity on the Australian diet as compared to the low-FODMAP and habitual diets, despite no observed increase in disease activity (i.e. stable fecal calprotectin). None of the diets affected fecal pH or SCFAs.

Authors noted the patterns of fecal microbiota change in this study resembled those observed in a cohort of IBS patients and healthy individuals in a previous study, saying, “It is reassuring that the same dietary manipulations of FODMAPs produce consistent effects irrespective of the underlying disease state.”

This study shows FODMAPs seem to induce functional GI symptoms in patients with clinically quiescent Crohn’s disease without changing disease activity. Although this observation is of interest, it may be of little clinical utility, since participants’ habitual (baseline) diets—which they had presumably adopted by trial-and-error to avoid worsening of symptoms—appeared to have the same effects as the low-FODMAP diet. Thus, those with inactive Crohn’s disease and no functional GI symptoms would lack a compelling reason to change their habitual diets. More study is required to confirm whether a low-FODMAP diet could lead to noticeable improvements for those with Crohn’s disease who do suffer from functional GI symptoms.


Halmos EP, Christophersen CT, Bird AR. Consistent Prebiotic Effect on Gut Microbiota With Altered FODMAP Intake in Patients with Crohn’s Disease: A Randomised, Controlled Cross-Over Trial of Well-Defined Diets. Clinical and Translational Gastroenterology. 2016; 7:e164. doi:10.1038/ctg.2016.22