Fiber-Metabolizing Bacteria Could Boost Gut Health in Celiac Disease

Celiac disease is an immune-mediated condition in which gluten, a protein in wheat products, causes inflammation in the small intestine. The only current treatment for celiac disease is for individuals to switch to a gluten-free diet.

Although this strategy minimizes disease symptoms, it can be low in fiber, which promotes gut health and function. While previous studies showed that individuals with celiac disease have distinct gut microbiomes from people without the condition, scientists have not explored the fiber-metabolizing capacity of this population or how fiber and its byproducts affect them.¹

In a study published in Nature Communications, researchers from McMaster University showed that people with celiac disease have reduced populations of fiber-metabolizing gut bacterial families.² In mice, the team demonstrated that the metabolism of specific fibers produced short-chain fatty acids (SCFAs) that promoted gut health, including decreasing inflammation from gluten sensitivity. The findings provide insights into how to improve gluten-free diets to increase proper gastrointestinal function and healing in people with celiac disease.

The researchers collected gut microbiome samples from 27 people with celiac disease: 16 had been recently diagnosed, and 11 had been diagnosed and adhering to a gluten-free diet for at least two years. They determined the microbiota composition using 16S rRNA sequencing and compared these samples to those of 26 healthy controls. The team showed that both groups of people with celiac disease had decreased expression of enzymes relating to degrading starch and dietary fiber, which coincided with a reduction in the amount of bacteria from the Prevotellaceae family.

Fiber metabolism by bacteria leads to the production of SCFAs, which can promote intestinal function. Using gas chromatography mass spectrometry, the researchers showed that people with a recent diagnosis of celiac disease had the lowest concentration of SCFAs. People who had followed a gluten-free diet for at least two years had higher concentrations of specific SCFAs compared to those with recent diagnoses, but lower than those in healthy controls.

The researchers suspected that the reduction in fiber-metabolizing bacteria could lead to a reduction in beneficial SCFAs in people with celiac disease. The team explored the role of fiber in a mouse model that was genetically susceptible to celiac disease. After sensitizing the mice to gluten to promote the characteristic immune response in the small intestine, the team placed the mice on a gluten-free diet with or without one of two types of fiber: inulin, a soluble plant fiber, or HylonVII, an insoluble fiber from corn starch.

Inulin supplementation decreased the number of lymphocytes in the intestinal epithelium and improved a marker of intestinal inflammation compared to mice only fed a gluten-free diet. These mice also had more SCFAs in their intestines. In contrast, HylonVII only improved the intestinal inflammation marker, suggesting that supplementing a gluten-free diet with inulin could potentially benefit those with celiac disease if the appropriate fiber-degrading bacteria are present.

Finally, to study the role specifically of the Prevotellaceae family identified in their human data, the researchers colonized germ-free, gluten-sensitized mice with 10 members of this family and compared their SCFA production on an inulin-supplemented gluten-free diet to non-colonized mice. Animals with the added fiber-metabolizing bacteria increased the amount of SCFAs in their intestines, confirming the importance of these species to proper fiber metabolism.

The researchers concluded that, although SCFAs from fiber can promote gut health even in individuals with celiac disease, the microbiomes of these people often do not include species that can metabolize fiber. Additionally, different types of fiber offer distinct benefits. These findings can help improve dietary recommendations for people with celiac disease.

“While a gluten-free diet remains essential for celiac disease, our findings suggest future therapies may also need to support the gut microbiome. We found reduced fibre-processing activity in the upper gut, the area damaged in celiac disease, which is surprising because this part of the gut has not traditionally been seen as a major site of fibre metabolism. This opens the door to combining dietary strategies like added fibre with probiotics that can metabolize it,” said Elena Verdu, a study coauthor and researcher who investigates the role of the gut microbiome on intestinal disorders, in a press release.