i read somewhere that the meal you eat, how fast it gets absorbed depends on how much fat and fiber is contained in the meal. Fat and Fiber will slow down absorption of everything, even your protein shakes. Regular meat doesn't have a high GI, but if you eat it w/ a bunch of simple carbs it will be absorbed much faster than if you would eat it w/ brocolli, lettuce etc. Point being it depends on what you eat your meal w/. We as bodybuilders want to maintain that anabolic state as long as possible, and if dieting want to maintain it on the fewest number of calories. So many diets i've seen that incorporate carbs and fats into the program will eat the obvious high protein, w/ carbs coming only from vegetables, and for fat a tablesppoon of flax, or extra virgin olive oil. This will slow down absorption time.
hope that helps