Is a Low-FODMAP Diet the Next Big Thing?

Which Patients Benefit?

While dietary intervention may be effective in reducing symptom severity in patients with IBS, not all patients respond. This raises the question as to which factors govern the response—and can we predict the response?

Certain subgroups of patients with IBS have an altered gut microbiota composition which can be further altered by variations in dietary composition. Thus, gut microbiome biomarkers may be associated with the efficacy of a low-FODMAP diet. Several investigators have noted that diets that differ in their FODMAPs content alter the colonic luminal microenvironment; therefore, the fecal bacterial profile of patients with IBS may predict responsiveness to a diet low in FODMAPs.

McIntosh and coworkers^[31] compared the effects of low- and high-FODMAP diets on the metabolome and the microbiome of patients with IBS. The IBS-SSS was reduced in the group receiving a low-FODMAP diet but not in those ingesting a high-FODMAP diet. The profile of urine metabolites also differed significantly. Of specific importance, histamine, an important pathophysiologic mediator and a measure of immune activation, was reduced eightfold in the low-FODMAP diet group; histamine is known to excite enteric cholinergic neurons and stabilization of mast cells, and histamine antagonists have been reported to improve IBS symptoms. In addition, the high-FODMAP diet decreased the relative abundance of bacteria involved in gas consumption, which could worsen symptoms.

Bennet and colleagues^[32] also determined that diets differing in FODMAPs content favorably affect gut bacteria and that the resultant bacterial profiles could predict intervention responses. Responders to the low-FODMAP dietary intervention were discriminated from nonresponders before and after intervention by their fecal bacterial profiles. Bacterial abundance tended to be higher in nonresponders to the low-FODMAP diet compared with responders. A low-FODMAP diet was associated with reduced Bifidobacterium and Actinobacteria in patients, correlating with lactose consumption.

Chumpitazi and colleagues^[33] determined the efficacy of a low-FODMAP diet in children with IBS, and whether gut microbial composition and/or metabolic capacity are associated with the outcome.Compared with baseline, children had fewer episodes of abdominal pain during the low-FODMAP diet and more daily episodes during the traditional diet. Responders were enriched at baseline in taxa with a known greater saccharolytic metabolic capacity (eg, Bacteroides, Ruminococcaceae, and Faecalibacterium prausnitzii).

Hustoft and coworkers^[34] also reported that in patients with diarrhea-predominant or mixed IBS, a blinded low-FODMAP diet improved the IBS-SSS and microbiome profile.

In addition, Staudacher and colleagues^[35] performed a randomized, placebo-controlled study to determine the effects of a low-FODMAP diet on symptoms and the fecal microbiota in patients with IBS.A higher proportion of patients eating the low-FODMAP diet had adequate symptom relief (57%) compared with the sham diet group (38%). The abundance of Bifidobacterium species was lower in fecal samples from patients on the low-FODMAP diet. It is unclear whether the changes noted were due to the collective FODMAPs restriction or removal of a single component, such as lactose.

In summary, diets differing in FODMAPs content have marked effects on gut microbiota composition. A low-FODMAP diet was associated with higher fecal pH (7.37 vs 7.16), greater microbial diversity, and reduced total bacterial abundance compared with the traditional diet.^[24] These prebiotic effects may benefit colonic health. This raises the question of whether a prebiotic supplementation would enhance the beneficial effect. Wilson and colleagues^[36] randomly assigned patients with IBS to three different interventions, noting significant differences between symptom relief at week 4 between controls (30%), those on a low-FODMAP diet alone (50%), and those on a low-FODMAP diet plus the prebiotic B-galacto-oligosaccharide(67%). The low-FODMAP diet plus the prebiotic group had markedly improved individual IBS symptoms. Furthermore, the investigators observed significant differences in fecal Bifidobacteria content between the low-FODMAP diet plus the prebiotic and sham groups.

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