Inulin is a type of prebiotic. It's not digested or absorbed in the stomach. It stays in the bowel and helps certain beneficial bacteria to grow.
Inulin is a starchy substance found in a wide variety of fruits, vegetables, and herbs, including wheat, onions, bananas, leeks, artichokes, and asparagus. The inulin that is used in supplements most commonly comes from soaking chicory roots in hot water.
People commonly use inulin by mouth for weight loss, constipation, and diabetes. It's also used for high blood fats, including cholesterol and triglycerides, and many other conditions, but there is no good scientific evidence to support most of these uses.