So, I can see that there's a couple of questions touching on this subject already, but none of them answer the aspect that I'm curious about:
Dietary fiber is a polymer composed of multiple starch molecules chained together, and starch molecules are polymers composed of multiple sugar molecules chained together, right?
So, why are our bodies are able to digest starches and not dietary fiber, when the process for digesting starches involves breaking up the starch polymers into sugar molecules? Why can't the same enzymes used to break down starches break dietary fiber down into its component starch molecules, or break individual sugar molecules off of the ends of them?
Is it simply a matter of time, and we simply pass put the partially-digested remains of the dietary fiber because it doesn't remain in our gut long enough to properly digest? I know that cows have multiple stomachs to facilitate the digestion of grass, but I also know that they've got symbiotic bacteria helping them out as well.