Inulin is not digested or absorbed in the stomach. It goes to the bowels where bacteria are able to use it to grow. It supports the growth of a special kind of bacteria that are associated with improving bowel function and general health. Inulin decreases the body's ability to make certain kinds of fats.
The addition of Inulin to the diet has been show to help reduce the absorption of fat by up to 50%, this is thought to be due to the action of inulin and fibre has on the gut bacteria helping to develop colonies of healthy gut flora specifically Bifidum bacteria which helps encourage better digestion and elimination of fats.
All inulin is not the same. Inulin is composed of a mixture of oligomers and polymers of different degree of polymerisation. What this means is that the composition of inulin in terms of chain length depends on its source. Chicory root inulin has a relatively longer chain than other types or sources of inulin. This provides several advantages over inulin with shorter chain lengths.