Even simple foods like Indian chapatis can be fermented if they are simply allowed to rise for a time, after being exposed to the natural yeasts that are everywhere.
And I look up studies, and come up with, as one example, this one: https://www.ncbi.nlm.nih.gov/pubmed/15562743
The presence of phytic acid and gluten are two of the arguments used against bread consumption. Gluten, too, seems to be predigested in most fermentation processes, which is what sourdough leavening is.
I have long made the self evident point that if bread were really that bad for you, it would not have become a staple in so many places. (and, obviously, the poor health of people who lived ONLY, or even mainly, on bread cannot be used as a valid argument, since anyone living ONLY on bread is going to be malnourished).
We take so much of what we do for granted. We take our bread, to take the present example, for granted. We assume that sanitized and industrialized yeast is how “bread is made”. But this is an invention of the past century, or perhaps the 19th at the latest.
It is odd to ponder how we are rediscovering the wisdom of our parents and those who went before them. Coleslaw and potato salad–cruciferous vegetables, and resistant starch, which is in effect a prebiotic. Resistant starch passes through the small intestine relatively intact, and then feeds the bacteria of the large intestine.
Pickles: probiotics. Same with yogurt, kefir, and other such foods, which also protect the immune system.