What is already known
Irritable bowel syndrome (IBS) is an inflammatory disorder of the gastrointestinal tract that causes stomach pain, wind, diarrhea and constipation. The disorder has been associated with dietary habits and a ‘leaky’ gut — a condition that allows partially digested food, toxins and bacteria to penetrate the lining of the gut. However, the exact cause of IBS isn’t well understood.
What this research adds
Researchers colonized gut organ cultures with microbiota samples from untreated IBS patients who followed a diet low in fermentable carbohydrates. The microbiota from these people regulated the intestinal expression of genes involved in inflammation and intestinal integrity. The team also identified Bifidobacterium adolescentis as a diet-sensitive microbe that can disrupt the gut barrier function.
Conclusions
The findings suggest that the gut microbiota mediates the beneficial effects of a diet low in fermentable carbohydrates, and they support the feasibility of microbial-based treatments for IBS.
More than 1 in 10 people worldwide suffer from irritable bowel syndrome, or IBS — an inflammatory disorder of the gastrointestinal tract that causes stomach pain, wind, diarrhea and constipation. Now, researchers have found that a diet low in fermentable carbohydrates can alter the human microbiota in ways that influence the expression of genes involved in inflammation and intestinal integrity.
The findings, published in Cell Reports, support the feasibility of microbial-based treatments, such as fecal microbiota transplants or targeted modifications of the microbiota, for treating IBS.
IBS has been associated with dietary habits and a ‘leaky’ gut — a condition that allows partially digested food, toxins and bacteria to penetrate the lining of the gut. But the exact cause of the disorder isn’t well understood.
Nissan Yissachar at Bar-Ilan University and his colleagues used a gut organ culture system, which they had previously developed, to investigate how the colon responds to microbiota communities collected from people with IBS who followed a diet low in fermentable carbohydrates, also known as low-FODMAP diet.
Diet effects
Previous studies showed that a low-FODMAP diet can ease some symptoms of IBS. The researchers confirmed that most of the 10 IBS patients enrolled in the study benefited from the diet.
The team collected and analyzed stool samples from patients before and after they started the diet. After the diet, their microbiota showed increased levels of Acutalibacter timonesis and Oscillibacter species and decreased levels of several other bacteria, including Eubacterium ventriosum, Clostridium disporicum and Bifidobacterium adolescentis.
To determine whether diet-induced alterations of the microbiota composition influenced the expression of specific genes in the gut, the researchers infused gut organ cultures with stool samples collected from some of the study participants. The post-diet microbiota appeared to increase the intestinal expression of genes involved in intestinal integrity. In contrast, the pre-diet microbiota seemed to increase the expression of genes implicated in inflammation.
Gene expression
Next, the team set out to assess whether microbiota-induced alterations in gene expression were linked to specific microbes. Out of 146 bacterial species identified in patient samples, 10 were associated with the expression of 113 host genes.
Among those, Bifidobacterium adolescentis was positively correlated with the expression of several genes involved in inflammation and the maintenance of the structural integrity of the gut lining.
When grown together with gut epithelial cells, B. adolescentis disrupted the continuous barrier between the cells. It also reduced the gut barrier function and increased gut permeability in mice. A low-FODMAP diet reduced the abundance of B. adolescentis in the gut, the researchers found.
“Our data support the hypothesis that the gut microbiota mediates the beneficial effects of low-FODMAP diet,” the authors say.
