Many people with celiac disease are advised to eat more fibre to support digestion and manage symptoms, either through diet or prescribed fibre supplements. New research from McMaster University shows that the benefits of that fibre may depend on whether the right bacteria are present in the gut to break it down.
The study, published in Nature Communications on March 31, found that people with celiac disease had significantly reduced capacity to metabolize dietary fibre in the small intestine. This is because they lacked a key fibre-degrading bacterial family called Prevotellaceae – organisms that help support gut healing and regulate inflammation.
This discovery was observed in both newly diagnosed people and in those who have been managing celiac disease for years with a gluten-free diet and suggests the lack of small intestinal bacteria such as Prevotellaceae is due to persistent microbiome disruptions linked to the disease itself, rather than diet alone.
"Originally, we thought that the problem was that people aren't getting enough fibre. Then we found out that people might not have the right bacteria to use the fibre that they're already eating. Adding more fibre won't be the solution unless you fix the underlying problems with using it," says Mark Wulczynski, first author of the study and postdoctoral fellow with McMaster's Farncombe Nutrition Initiative .
Celiac disease is a disorder where eating gluten drives inflammation in the small intestine. It impacts approximately one per cent of the Canadian population , with the only current treatment being a strict gluten-free diet. This is particularly noteworthy because the research suggests that removing gluten alone doesn't fully restore the gut's microbiome functional capacity.
Future therapies may need to combine dietary strategies with microbiome‑directed approaches, such as microbial restoration or targeted probiotics.
"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," says senior author Elena Verdu , professor with McMaster's Department of Medicine and director of the Farncombe Family Digestive Disease Health Research Institute.
Not all fibre is alike
Using preclinical models, the researchers investigated which fibre types are actually helpful for healing the gut. They found inulin – a fibre found in everyday foods like bananas, chicory root, garlic and onions – accelerated healing of gluten-induced intestinal injury by feeding the small intestinal microbiome.
This effect occurred only with the right fibres in the diet. Another source of fibre, Hylon VII, a type of corn-based resistant starch commonly used in food manufacturing, did not affect the microbiome and promote healing in the same way inulin did.
This comparison suggests the type of fibre, not just the quantity, may be important for people with celiac disease
To verify this in patients, researchers collected small intestinal fluid from three groups: people newly diagnosed with celiac disease, people who had followed a gluten-free diet for more than two years, and healthy controls. They analyzed the microbiome in these samples to determine which bacteria were present and whether they carried the genes needed to break down different types of fibre. They also compared these findings with participants estimated dietary fibre intake and with measurements of plant DNA in stool, providing an objective marker of fibre sources in the diet.
The results showed that most individuals, including both healthy controls and celiac patients, consumed less fibre than recommended by Health Canada. Health Canada recommends 25-38g of fibre per day for healthy women and men, respectively, but there are no evidence-based recommendations for different disease states. Diseases may cause the body to be more active and simultaneously less efficient than usual, affecting nutritional needs.
However, celiac patients, whether newly diagnosed or treated with a gluten-free diet, showed a distinct combination of low fibre intake and a lack of bacteria known to break down fibre in the small intestine. This suggests that supporting gut health in celiac disease may require both the right fibre and the right bacteria in the small intestine, known as a synbiotic approach.
Future research is needed to better understand and determine how fibre and microbial restoration could improve symptoms, healing, and treatment responses, before making clinical recommendations.
The study was funded by a Canadian Institutes of Health Research grant and a J.A. Campbell Young Investigator Award to Mark W. from Celiac Canada. Verdu Holds a Canada Research Chair in Microbial Therapeutics and Nutrition in Gastroenterology.
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