Inulin is natural fibre, from the chicory root, it's a fructane used as food fibre, but it has a secret:
Orafti®HSI Inulin is a standard polymerisation fructan, with very high solubility rates reflected in the final product result; and a sweetness level of 30%.
Inulin acts as a natural sweetener, because thanks to its content of 12% fructose oligomers, it sweetens without the need to add sugars to the product.