Here's what I can tell ya:
My information comes from the South Beach Diet book(starting on page 52). "The faster the sugars and starches (carbs) are processed and absorbed into your bloodstream, the fatter you get. Anything that speeds the process by which your body digests carbohydrates is bad for your diet, and anything that slows it down is good....Example: Raw broccoli is crunchy, hard, cold and covered with nutritious fiber. If you eat it that way, your stomach has really got to work in order to get at the carbs." Compare that to the work your stomach does to process boil or steamed to a mush broccoli.
In the case of processed foods, digestion begins before it reaches the store shelf. With white bread, first the wheat is stripped of bran and fier. The it's pulverized into the finest white flour. The baking process puffs it up into light, airy slices of bread. No wonder your stomach makes such quick work of it. A slice of white bread hits your bloodstream with the same jolt you'd get by eating a tablespoon of table sugar right from the bowl! .... Real old-fashioned bread - the coarse, chewy kind with a thick crust and visible pieces of grain... puts your stomach to work."
Read the bread label carefully. Wheat doesn't always mean Whole Wheat. See if one of the first ingredients says Enriched wheat. If it does, stay away! If should not say enriched... the enriched part means the digestion process has already taken place when the bread was made... eat a spoon full of sugar (just kidding) LOL!
This is where the glycemic index comes in. In a nutshell, the glycemic index gives foods a number. The lower the number the slower the sugar is absorbed into the bloodstream and vice versa.
If you can get your hands on a the South Beach Diet book, read the chapter entitled, It's Not Just What You Eat, It's How You Eat It. That chapter taught me more about foods than I learn in my undergraduate program....Home Economics!