A Common Type of Fiber May Trigger Bowel Inflammation

Inulin, a type of fiber found in certain plant-based foods and supplements, causes inflammation in the gut and exacerbates inflammatory bowel disease in a preclinical model, according to a recent study by Weill Cornell Medicine investigators. The surprising findings could pave the way for therapeutic diets that may help ease symptoms and promote gut health.

The study, published in the Journal of Experimental Medicine, shows that inulin — found in foods like garlic and leeks, commonly used fiber supplements and foods with added fiber — stimulates microbes in the gut to release bile acids that increase the production of molecules that promote intestinal inflammation.

Dietary fiber, including inulin, is considered an essential part of a healthy diet for most people. Gut microbes turn dietary fiber into short-chain fatty acids that turn on regulatory T cells, immune cells that help reduce inflammation and have other beneficial effects throughout the body. Because of these benefits, there has been a remarkable rise in use of dietary fiber as an additive in both foods and supplements, and purified inulin or inulin-rich chicory root is often the main source of the fiber.

“Inulin is now everywhere, from clinical trials to prebiotic sodas,” says the lead author of the study, Dr. Mohammad Arifuzzaman, assistant professor of immunology in medicine.

Dr. Arifuzzaman and his colleagues expected that inulin would also have protective effects in inflammatory bowel disease. But they found just the opposite.

In preclinical models of inflammatory bowel disease, the introduction of inulin set off a chain reaction, causing the immune system to produce cells called eosinophils, which can increase inflammation and tissue damage. While a 2022 study by the same team of investigators showed that this flood of eosinophils may help protect against parasite infection, in the inflammatory bowel disease model, it exacerbated intestinal inflammation, weight loss and other symptoms like diarrhea.

Translational patient-based studies also showed that patients with inflammatory bowel disease had higher levels of bile acids in their blood and stool and excessive levels of eosinophils in their intestine compared with people without the condition.

These unexpected discoveries not only may help explain why high-fiber diets often exacerbate inflammatory bowel disease in patients, they may also help scientists develop therapeutic diets to reduce symptoms and gut damage in patients with inflammatory bowel disease or related conditions.

“The present study shows that not all fibers are the same in how they influence the microbiota and the body’s immune system,” says senior author Dr. David Artis, director of the Jill Roberts Institute for Research in Inflammatory Bowel Disease and director of the Friedman Center for Nutrition and Inflammation, both at Weill Cornell Medicine, and Michael Kors Professor in Immunology.