Well, first of all I'm not a scientist, and I'm just going off of what I hear from more educated people on the matter - and also Google helps.

Aoparently a lot of different testing has been going on in recent years, with mixed results.

But the general trend appears to be this: the more refined and processed the product, the more vulnerable it is to structural changes under heat, away from dietary fiber, and into something digestible. So heating the dietary fiber in a tortilla would make it more vulnerable to adjustment than heating the dietary fiber in a raw Romaine leaf the same way, for example.

It also appears that the method of heat application seems to matter. Microwave heating appears to have less of an effect, while more typical oven heat or presumably also stove top heat (same redshift idea) has a greater effect. It also appears that these alterations begin around 140 degrees Fahrenheit and increase with more heat, which also happens to be pretty much where the underlying chemical reaction that we observe as "browning" occurs, so that's probably related, and I'm sure a chemist could tell you a lot more about that than I could.