It does not remove the fiber but it changes the structure. The natural structure is like a balloon with good stuff inside. The digestion process breaks down tho

It does not remove the fiber but it changes the structure. The natural structure is like a balloon with good stuff inside. The digestion process breaks down those balloons one at a time and liberates the contents. That process slows down the absorption of sugar. Blending pops all of the balloons so you everything can be accessed/absorbed at the same time, leading to sugar spikes, etc...