Preserving amylase foods for long periods at low temperatures (41° Fahrenheit) stimulates retrogradation. Something similar occurs with food drying processes. Dry bread, for example, loses its humidity and stimulates starch retrogradation, as in the case of toasted bread.
Although retrogradation does not wholly reverse food gelatinization, it does contribute to lowering foodstuffs’ Glycemic Indexes. Spaghetti (even white refined), for example, will have a 35 Glycemic Index if cooked al dente and eaten cold (in salads).
As we can see, the same bread (made from the same flour) can have a different GI depending on how it is prepared: freshly baked and still oven hot, dried or toasted. Fresh bread when frozen and thawed out at room temperature will also have a much lower GI.