People with celiac disease are often encouraged to eat more fiber to support digestion and gut health. But new research suggests that advice may not work the same way for everyone.
A study published in Nature Communications found that some individuals with celiac disease may lack key gut bacteria needed to break down fiber. Without those microbes, simply increasing fiber intake may not deliver the expected benefits.
Celiac disease is an autoimmune condition in which gluten triggers inflammation and damage in the small intestine. While a strict gluten-free diet remains the only treatment, many people continue to experience digestive symptoms even after removing gluten.
Researchers from McMaster University analyzed samples from people newly diagnosed with celiac disease, those following a long-term gluten-free diet and healthy controls. They found that people with celiac disease had a reduced ability to metabolize dietary fiber in the small intestine.
“Originally, we thought that the problem was that people aren't getting enough fibre,” said Mark Wulczynski, a postdoctoral fellow with McMaster’s Farncombe Nutrition Initiative.
The findings suggest the issue may not be intake alone, but whether the body can actually use that fiber. The researchers found lower levels of bacteria from a group called Prevotellaceae, which are involved in breaking down fiber and may help regulate inflammation.
“Adding more fibre won't be the solution unless you fix the underlying problems with using it,” Wulczynski said.
The study included both human samples and preclinical models. In laboratory experiments, the researchers tested different types of fiber and found that inulin, a fiber found in foods like bananas, garlic, onions and chicory root, supported healing in the small intestine by feeding beneficial microbes.
However, a corn-based resistant starch commonly used in food manufacturing did not produce the same effect, suggesting that the type of fiber may matter as much as the amount.
The researchers also found that most participants, including those without celiac disease, consumed less fiber than recommended. But people with celiac disease showed a combination of lower fiber intake and reduced levels of fiber-degrading bacteria, which may further limit how well fiber works in the body.
The findings point to a more complex picture of how diet and the microbiome interact in celiac disease. Future approaches may need to combine dietary changes with strategies that support or restore beneficial gut bacteria, such as targeted probiotics or microbial therapies.
However, the researchers note that more studies are needed before making clinical recommendations, particularly to determine whether these approaches improve symptoms or long-term outcomes in people with celiac disease.
This study was supported by the Canadian Institutes of Health Research and Celiac Canada.