Inulin fibre worsens inflammatory bowel disease, finds study

The study, published in the Journal of Experimental Medicine, showed that inulin, which is found in foods like garlic, and leeks, as well as commonly used fibre supplements and foods with added fibre, 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 inulin and other dietary fiber types into short-chain fatty acids that turn on immune cells called regulatory T cells, which help reduce inflammation and have other beneficial effects throughout the body.

One such protein, called IL-33, causes immune cells called group 2 innate lymphoid cells (ILC2s) to become activated, triggering an excessive immune response similar to an allergic reaction. That excessive immune response then exacerbates intestinal damage and symptoms in an animal model of inflammatory bowel disease.

In the study, feeding inulin to mice in the model of inflammatory bowel disease increased the production of certain bile acids by specific groups of gut bacteria. The increased bile acids boosted the production of an inflammatory protein called IL-5 by ILC2s. In response to these changes, the immune system promotes the production of immune cells called eosinophils, which further ramp up inflammation and tissue damage. However, in the inflammatory bowel disease model, this chain reaction exacerbated intestinal inflammation, weight loss, and other symptoms like diarrhea.

This analysis revealed that patients with inflammatory bowel disease like the mice fed inulin, had higher levels of bile acids in their blood and stool and excessive levels of eosinophils in their intestines compared with people without the condition.

The results suggested that the inflammation cascade similar to that in the mice fed inulin is already primed in humans with inflammatory bowel disease, and dietary uptake of inulin may further exacerbate the disease.

Reference: Arifuzzaman, M., et al. (2024). Dietary fiber is a critical determinant of pathologic ILC2 responses and intestinal inflammation. The Journal of Experimental Medicine. doi.org/10.1084/jem.20232148.