You know, I’ve even put sugar and honey in some homemade bread recipes (in relatively small quantities), and anything that is naturally leavened (and long-fermented) seems to have markedly less effect on my BG. I suspect that the sourdough process breaking down starches and sugars really helps.
I’m in Switzerland now, where even the “big bakeries” (like Reinhard) make all their breads in traditional ways. Now, lots of those breads are made with a poolish or biga or starter, and they tend to be whole-grain and incorporate seeds and nuts, but they are as commercial as one can get. Guess what… other than the “croissants” (which are actually Gipfeli and just look and taste like croissants, but definitely aren’t according to the Swiss), none of the breads here spike me like the stuff back in the good old U.S. of A.
It’s some kind of flour conspiracy! But I suspect it mostly has to do with the American trend towards short bulk fermentation (instant yeast), exclusive use of white all purpose or bread flour (with all the bran and germ sifted out), and maybe other additions. But yeah, my three-days-to-make sourdough from a natural starter I captured a while back is pretty low-GI by all evidence I have.