In 1979, researchers at the University of Kentucky studied 20 men with type 2 diabetes, all of whom had been taking an average of 26 units of insulin per day. The experimental diet included plenty of vegetables, fruits, whole grains, and beans, so it was high in fiber and carbohydrate. The diet was nearly vegetarian, with very little animal fat—in fact, very little fat of any kind. After just 16 days on the program, more than half of the men were able to stop taking insulin entirely, and their blood sugar levels were lower than before.4
Let’s say we are making bread dough. We add a bit of yeast to the flour to make the bread rise. The yeast causes many tiny air pockets to form, which is what makes bread different from, say, a shingle. Now, as you eat the baked bread, your stomach acid and digestive enzymes enter those air pockets and rapidly break the molecules of flour into individual sugar molecules that then pass from your digestive tract into your bloodstream. Even whole wheat bread, with shreds of fiber remaining, is easy pickings for digestive enzymes—they have no difficulty entering the air pockets and digesting the starch in the bread. Pasta is different. It is not made with yeast, so it has no air pockets. If bread is like a pile of tiny twigs, ready to ignite with a single spark, pasta is like a cord of logs—it is much more compacted and “catches fire” more slowly. Even if you chew pasta thoroughly, there is no way it can digest as rapidly as bread—and that’s why it has a lower GI.