For people with inflammatory bowel disease (IBD), a meal can become a source of uncertainty. Dairy or wheat products that once seemed harmless may bring bloating, pain or diarrhea, even when Crohn's disease or ulcerative colitis appear to be in remission. These reactions may be the product of inflammation that changes how gut bacteria process food, a new study shows.

The study investigated how intestinal inflammation and the gut microbiome might contribute to food-related symptoms.

Mice with colitis that were exposed to dairy or gluten developed immune responses to those foods. Researchers traced this pattern to changes in gut bacteria.

First, the research team developed inflamed intestines in mice, using two mouse models of colitis, a form of intestinal inflammation. Then the mice were exposed to dairy or gluten and went on to develope immune responses to those foods.

When the foods were introduced again, the animals experienced heightened gut sensitivity and worsening colitis symptoms. The researchers traced this pattern to changes in gut bacteria. Inflammation reduced bacteria that normally help break down components of dairy and gluten.

When gut microbes from inflamed mice were transferred to mice raised without microbes, the recipients became more susceptible to food sensitization. Restoring some of the depleted bacteria reduced reactions in these experimental models.

Humans with intestinal inflammation were the focus of the next aspect of the study. The team examined 104 people with IBD who were in remission — 58 with Crohn's disease and 46 with ulcerative colitis — and compared them to 44 people without IBD. Participants answered questions about food intolerances and digestive symptoms and provided stool samples for analysis.

About 85 percent of the participants with IBD reported food-related triggers, compared with only a third without IBD. Those with IBD had differences in their gut microbiota, including lower micro-biodiversity and fewer bacteria associated with breaking down certain food components. In laboratory tests, stool samples from people with IBD were less effective at breaking down milk proteins, particularly among those who reported food intolerances.

There are reasons for the reaction. "The microbiome acts as a metabolic organ, helping us digest food components, including those that can trigger gut reactions. Our study shows that inflammation impairs this microbial digestive capacity, potentially contributing to adverse food reactions and opening new possibilities for microbiome-based therapies to restore this function in IBD patients," Caminero said in a statement released by the American Gastroenterological Association.

These results offer a possible explanation for why digestive symptoms can persist even when IBD is considered in remission. They also suggest that, for some patients, the problem may involve more than the food itself: inflammation may alter the microbes that would normally process food components before they provoke an immune response.

That said, the findings in humans only show an association between inflammation and changes in gut microbes, not proof that these bacterial changes cause food intolerance.

For those living with IBD, this study is not a reason to automatically eliminate dairy, wheat or gluten. Broad food restrictions can make it harder to get adequate nutrition.

Food-related symptoms can have multiple explanations, and the researchers note that genetics, infections and stress may contribute. The animal experiments are promising, but treatments that restore particular bacteria have not yet been shown to work safely and effectively in people.

For those living with IBD, the findings of this study are not a reason to automatically eliminate dairy, wheat or gluten. Broad food restrictions can make it harder to get adequate nutrition. If a food seems to trigger symptoms, keep a food and symptom diary and discuss the pattern with your gastroenterologist or an IBD-experienced dietician.

Going forward, researchers are exploring whether selected bacteria, potentially delivered through microbiome-based treatments, might help reduce food-related reactions. For now, the study provides a promising lead, not a ready-made therapy. The practical message for IBD patients is to take IBD symptoms seriously, but avoid unnecessary dietary changes without professional guidance.

The study is published in the journal, Gerontology.