This from Cheryl Maffei in an interview with Amy Halloran on the Wordloaf substack:
Going out to dinner with my dad, when bread would come to the table he would grab a piece, and if you could take the center out and make it look like dough again, we couldn’t eat it. It was deemed fundamentally undigestible, and this is before any of us knew anything about sourdough.
Try it for yourself. With naturally fermented bread the dough will just spring back to its original shape, but with shop brought cheap white bread it will seem to become dough again.
(Source: digitalcommonwealth.org/search/commonwealth-oai:gm80md45g)