Low-FODMAP diet shifts metabolome, microbiome in IBS patients

Last Updated: 2016-03-31

By Anne Harding

NEW YORK (Reuters Health) - Irritable bowel syndrome (IBS) patients show changes in their metabolome and microbiome after three weeks on a diet low in fermentable oligosaccharides, disaccharides and monosaccharides and polyols (FODMAPs), according to new findings.

"The diets cause changes in the microbiome, and these changes could play a role as well in improving symptoms and also could have some long-term effects that potentially have health implications, but we don't know yet," Dr. Stephen Vanner of Kingston General Hospital in Kingston, Ontario, Canada, told Reuters Health in a telephone interview.

Several studies have shown that diets high in FODMAPs can bring on IBS symptoms, while low-FODMAP diets can improve symptoms in many patients. But the mechanism behind these effects remains unclear, Dr. Vanner and his team note in their report online March 14 in Gut.

To investigate, the researchers looked at how three weeks on a high- or low-FODMAP diet affected symptoms and the metabolome and microbiome in 40 patients, 37 of whom completed the study.

The 18 patients on the low-FODMAP diet had a 28% reduction (p<0.001) in IBS symptom severity scoring (SSS), on average, while the high-FODMAP group had a 7% increase in IBS SSS, which was not statistically significant. Seventy-two percent of the low-FODMAP group had a 50% or greater reduction in symptoms, versus 21% of the high-FODMAP group (p<0.009).

Urine testing found a significant separation in the metabolic profiles of the two groups after three weeks on the diet. The low-FODMAP group had an eight-fold reduction in urinary histamine (p<0.05), and their levels of p-hydroxybenzoic acid and azelaic acid were also significantly different than levels in the high-FODMAP patients.

Stool microbiota composition also differed between the two groups after three weeks on the diet, with greater Actinobacteria richness and diversity in the low-FODMAP group and a greater relative increase in bacteria involved in gas consumption in the high-FODMAP patients.

FODMAPs include lactose, fructose, fructans, galactose, and oligosaccharides, Dr. Vanner explained, many of which are found in healthy foods including certain fruits, vegetables, beans, and lentils. The low-FODMAP diet is very restrictive and not intended to be long-term, he said. Instead, patients stay on the diet for three to four weeks to determine if it helps reduce their symptoms, and then gradually begin reintroducing foods to determine which types worsen their symptoms.

There are a few different ways that FODMAPs can affect digestive function, the researcher added. Some sugars aren't broken down during digestion until they reach the colon, where bacteria break them down into gases that can cause distention and discomfort, he said.

Short-chain fatty acids can also reach the colon, where they can signal to the intestinal lining, immune system, and nervous system. Also, he added, the findings show that FODMAPs can increase histamine levels in some patients, which can also affect nerves in the gut, causing pain and changes in motility.

"By manipulating FODMAPs we're manipulating immune signaling to nerves and decreasing symptoms," Dr. Vanner said. The next steps in the research, he said, will be to refine low-FODMAP diets to better identify the offending agents, and also look for ways to predict which IBS patients will benefit from a low-FODMAP diet.

The Canadian Institutes of Health Research supported this study. The authors made no disclosures.

SOURCE: http://bit.ly/1TkNesV

Gut 2016.