light bread starts turning into sugar almost instantly in the mouth and stomach. It's only one step removed and saliva can break it down quickly because it has amylase. Sour dough and whole wheat/grain breads tend to break down a bit slower. You can freeze bread overnight and make it a bit more "resistant" to breaking down quickly and I pretty much do this with all my breads along with toasting them a bit for sandwiches. Pasta can similarly have its glycemic index lowered by first making it "cold"

Do you mean that they need to be cold when they are consumed, or is it the process of freezing itself that does something, even if it's later reheated?

The process of cooling down converts starches in rice, pasta, potatoes etc... to a more resistant forms that your body cannot process easily.

Does chilling also work to convert bread starches into resistant ones, or does it only work for rice and potatoes?

GP mentioned bread specifically. I looked up some studies, and they are in agreement: https://pubmed.ncbi.nlm.nih.gov/17426743/

A starch is a starch.

However, this study seems to compare freshly baked bread to a frozen/toasted one.

I'd guess that the difference will be smaller when regular store-bought bread is used instead.

They don’t need to be cold when consumed.