IBS: Gut Bacteria May Predict Who Benefits From FODMAP Diet

Megan Brooks

October 24, 2016

A fecal bacterial profile could help identify which patients with irritable bowel syndrome will respond to a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols, known as FODMAP, new research shows.

"The low-FODMAP diet has been shown to alleviate symptoms in a number of patients, but of course there are some patients who don't respond," said Sean Bennet, PhD, from the University of Gothenburg in Sweden.

In this study, fecal samples and bacterial profiles were used to try to "predict who is likely to respond favorably to these quite arduous changes in diet," he told Medscape Medical News. Low-FODMAP diets restrict the consumption of bread, pasta, and certain other foods.

The results were presented at United European Gastroenterology Week in Vienna.

Predicting Response

Dr Bennet and his colleagues followed 61 patients with moderately severe or severe symptoms of irritable bowel syndrome. Thirty patients ate a diet traditionally recommended for patients with irritable bowel syndrome for 4 weeks and 31 ate a low-FODMAP diet. Fecal samples were collected before and after the dietary interventions, and food intake was recorded in diaries before and during the study period.

The GA-map Dysbiosis Test, which measures the signal intensity of 54 DNA probes targeting 300 or more bacteria on different taxonomic levels, was used to evaluate fecal bacterial composition.

A dysbiosis index score was assigned to each patient on the basis of bacterial profile. A score of 1 or 2 indicated normal microbiota composition, and a score of 3, 4, or 5 indicated microbiota imbalance, or dysbiosis.

At baseline, 20 patients in the FODMAP group and 25 patients in the traditional group had dysbiosis.

Table. Effect of Diet on Dysbiosis

Outcome FODMAP Group (n = 20) Traditional Group (n = 25)
Improvement 3 10
Worsening 11 6
No change 6 9


Patients who did not respond to the low-FODMAP diet had more severe dysbiosis at baseline than responders.

The traditional diet had no effect on overall bacterial composition, but in the FODMAP group, there was a significant reduction in potentially beneficial Bifidobacterium. This was more prominent in nonresponders than in responders.

Patients who did not respond to the low-FODMAP diet had "more abnormalities in their gut bacterial profiles before they started the diet than those who responded to the diet," Dr Bennet said in a statement. "This raises the possibility that fecal bacterial profiling could be undertaken before dietary interventions are considered."

"Being able to predict whether a patient is unlikely to respond to a low-FODMAP diet means that other therapies could be discussed earlier, and these patients could be spared a demanding diet that might have no effect, or even worsen, their symptoms," he added.

An Emerging Field

The low-FODMAP diet has been shown to improve symptoms of irritable bowel syndrome in some patients, but there are no long-term data showing the effect of a low-FODMAP diet eaten for 8 weeks or 12 weeks at 6 years. And "that's what matters," said Purna Kashyap, MBBS, from the Mayo Clinic in Rochester, Minnesota.

Dietary interventions are useful in patients with irritable bowel syndrome, but the ideal dietary management strategy is unclear, said Dr Kashyap, who studies the mechanisms by which gut microbes influence gastrointestinal motility in health and disease, but was not involved in this study.

"Having a microbial biomarker to predict who is going to respond better would be helpful," he told Medscape Medical News. "But we have to keep sight of the long view, which is that we still don't know how FODMAP works. Do we really need a low-FODMAP diet, or can we break it down into individual components and maybe use a milder dietary intervention that would be equally effective?"

"This is an emerging field, but microbial biomarkers are slowly entering mainstream arena. The main problem with it entering the mainstream clinical side right now is standardization," Dr Kashyap explained.

The study had no funding. Dr Bennet and Dr Kashyap have disclosed no relevant financial relationships.

United European Gastroenterology (UEG) Week: Abstract OP003. Presented October 17, 2016.

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