Both soluble fiber (like pectins) and insoluble fiber (like cellulose) are necessary to form a gel-like barrier in the intestine that prevents nutrient absorption.

“you need both to make that gel so the insoluble fiber formed the latticework like the net let's say you put a layer of petroleum jelly on a strainer you would have an impenetrable water barrier right yeah so the insoluble is like the strainer and the soluble becomes the thing that fills in the lattice that's right exactly so when you have both it works and there's data that shows that if you have either one or the other doesn't work you need both”