For many people with inflammatory bowel disease, foods that were once easy to tolerate can suddenly seem to cause problems.
A new study suggests changes in the gut microbiome may be part of the reason.
Researchers found that intestinal inflammation reduced certain bacteria involved in breaking down food components. In mice, that made immune reactions to dairy and gluten more likely. People with inflammatory bowel disease, or IBD, who reported food intolerances also showed signs of reduced microbial ability to process common trigger foods.
The study, published in Gastroenterology, does not show that inflammation causes food intolerance in everyone with IBD or that people with Crohn’s disease or ulcerative colitis should avoid dairy, gluten or other foods. Most of the strongest evidence came from mouse experiments, while the human findings were observational.
One study author, Dr. Neeraj Narula, reported receiving honoraria from several pharmaceutical companies.
IBD includes Crohn’s disease and ulcerative colitis, both of which involve inflammation in the digestive tract. Many people with IBD report symptoms they associate with foods such as dairy, wheat and fiber.
To explore why that may happen, researchers used two mouse models of colitis. After inflammation, exposure to dairy or gluten proteins was more likely to trigger an immune response. When the foods were introduced again later, the mice also had greater gut sensitivity and worse symptoms.
The researchers then looked at the microbiome.
Inflammation had reduced some of the bacteria that normally help break down those food components. When gut bacteria from inflamed mice were transferred into germ-free mice, the recipients became more prone to similar food reactions. Restoring some of the missing bacteria reduced that effect.
“The microbiome acts as a metabolic organ, helping us digest food components, including those that can trigger gut reactions,” said study author Alberto Caminero of McMaster University.
The researchers also found a similar pattern in people with IBD. Those who reported food intolerances were more likely to have fewer bacteria involved in processing common trigger foods.
That does not prove those microbiome changes caused their symptoms. Food reactions in IBD can have many causes, including genetics, infections, stress and other changes in the gut.
The findings also do not mean dairy or gluten are inherently harmful for people with IBD.
Instead, the study suggests that after inflammation, the gut may handle certain foods differently than it did before.
That could help explain why a food tolerated for years may suddenly become troublesome, even after an IBD flare has eased.
More research in people is needed to determine how often this happens, which foods are most affected and whether restoring certain gut bacteria could help.
For now, the study adds to the idea that food reactions in IBD may depend not only on what someone eats, but also on the condition of the gut itself.
The study was funded by Crohn’s and Colitis Canada and the Canadian Institutes of Health Research. Additional researchers received fellowship or institutional support from the Farncombe Family Digestive Health Research Institute, Triangle, Crohn’s and Colitis Canada, CIHR and McMaster University.