You should know about Stevia. Stevia as a partial sugar replacement in muffins can up the fiber content by four times.
A recent study published in LWT-Food Science and Technology, details a Stevia muffin retained the quality of a full sugar formulation with 30% sucrose replaced by Stevia variety rebaudioside A. Stevia has GRAS (Generally Recognized As Safe) status in the USA and can be used in baked goods. Last November the European Union, approved Stevia and said it can be used in 31 food categories, including high-fiber breakfast cereals.
by Dr, Earl Mindell