Reference
Chumpitazi BP, Cope JL, Hollister EB, et al. Randomised clinical trial: gut microbiome biomarkers are associated with clinical response to a low FODMAP diet in children with the irritable bowel syndrome. Aliment Pharmacol Ther. 2015;42(4):418-427.
Design
Randomized, double-blind, crossover study
Participants
Thirty-three children (age 7-17 y) with irritable bowel syndrome (IBS) per the ROME III gastrointestinal (GI) questionnaire
Study Parameters Assessed
All participants ate their habitual diet for 7 days to establish baseline. Stool samples to determine microbiome taxa were obtained. Diet 1 or Diet 2 was then ingested for 48 hours; a 5-day washout period ensued during which habitual diet was consumed, then participants were crossed over to the other diet. Diet 1 consisted of a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) containing 9 g per day of FODMAPs. Diet 2 consisted of a typical American childhood diet (TACD) containing a maximum of 50 g per day of FODMAPs.
Primary Outcome Measures
Abdominal pain frequency was the primary outcome measure assessed through a pain and stool diary over 24-hour periods during baseline and during the 2 days of each dietary intervention.
Secondary outcome measures included associated symptoms like bloating, flatus, nausea, and heartburn.
Baseline gut microbial composition (revealed through 16S rRNA sequencing) and metabolic capacity of the organisms were determined. Comparison of baseline microbiome was divided into a responders group (≥50% decrease in abdominal pain frequency on low FODMAP diet only) vs a nonresponders (no improvement during either intervention) group.
Key Findings
Comparing the diets, there was less abdominal pain during the low-FODMAP diet vs the TACD (1.1±0.2 standard error of the mean [SEM] episodes/d vs 1.7±0.4 SEM episodes/d, P<0.05). There were also fewer episodes of abdominal pain on the FODMAP diet (P<0.01) and more episodes on the TACD (P<0.01) when compared to baseline. Responders’ microbiomes were more enriched with taxa with greater ability to ferment (eg, Bacteroides, Ruminococcaceae, Faecalibacterium prausnitzii).
Practice Implications
The concept of IBS in children has recently been proposed by Sandhu et al.1 A low-FODMAP diet has been used as treatment in adults with IBS.2-4 Thus far, any application of a low-FODMAP diet in children has been based on studies in adult populations. This study by Chumpitazi and colleagues confirms that there may be a therapeutic role for low-FODMAP diet in pediatric IBS. It also sheds light on the role of the microbiota in the application of a low-FODMAP diet in childhood IBS.
The authors of this study had previously shown a benefit for children following the FODMAP diet in a small open-label trial.5 They observed that children whose symptoms responded best to a low-FODMAP diet had a different microbiota composition than those whose symptoms were nonresponsive. These preliminary findings prompted the current randomized, double-blind, crossover trial reviewed here.
Ultimately, we must keep in mind that by restricting fermentative carbohydrates over extended periods (months or years), we may also be creating long-term risks through changes in the colon environment.
The current trial corroborates the authors’ supposition that the benefit of a low-FODMAP diet is associated with a particular bacterial composition. The responders possessed microbes from several taxa, including Bacteroides, Ruminococcaceae, Faecalibacterium prausnitzii, and Dorea, all of which have a greater fermentative potential. The nonresponders had a greater number of the genus Turicibacter, which are known to have a lower fermentative capacity. This suggests that nonresponders have a bacterial composition that ferments less; therefore, removing fermentable carbohydrates will have very little impact on their IBS symptoms.
This study introduces the concept of a more individualized approach to the use of the low-FODMAP diet. Ideally, someday clinicians may be able to assess the microbiome before starting the FODMAP diet, perhaps sparing some children (or adults) the stress of such a restricted diet.
While the FODMAP diet may control symptoms in patients with IBS,6 the diet should be used with some caution. Applying the low-FODMAP diet (and/or the Specific Carbohydrate Diet) for extended periods of time has not been proven safe in any long-term studies. The concern is that many of the FODMAP foods that are restricted (eg, legumes, garlic, some whole grains) are critical to the health of the gut.7 Fermentable carbohydrates increase bacterial diversity in the colon, promoting the growth of Firmicutes, Bacteroides, and Bifidobacterium. These bacterial species produce short-chain fatty acids—proprionate, butyrate, and acetate—all of which are necessary for a healthy gastrointestinal tract. A recent study demonstrated that an altered microbiota occurs after patients have been on the low-FODMAP diet for as little as 21 days.8 The authors of the current study urge caution in reducing FODMAPs in the long term.
As clinicians, we need to first do no harm to our patients. As this study has shown, the application of a low FODMAP diet may ameliorate IBS symptoms, for some in as little as 48 hours. If this study had kept the children on a low-FODMAP diet for 7 days, as is commonly done in adults, we might have seen a greater response to the diet.
Ultimately, we must keep in mind that by restricting fermentative carbohydrates over extended periods (months or years), we may also be creating long-term risks through changes in the colon environment, including increased inflammation and even colorectal cancer.9-12 Our goal, as always, is to help bring the patient back to optimal health so that a varied diet can be resumed.
