Quick oats (cooks in 5 minutes) differ from regular (15 minutes of boiling) oats in that they have been cut into several pieces and then rolled until they are very thin. Therefore, they will require less cooking time.
Instant oats (1 to 1-1/2 minutes of cooking) differ from Quick Oats in that they have undergone extra steaming to pregelantinize the starch so that it is rehydrated faster during the cooking process. As for additives, SOME companies will add in salt, starch and defatted wheat germ. I checked my Instant Quaker oats, and it did not mention having any of these additives so it may be a varying factor between manufactures. If the additives are not added in, then nutritional value is the same for all of the oats...the only difference would be the physical processes used to decrease the size of the groats...and also steaming for the instant.
The reason for the increased GI rating will be due to a couple of things:
1. Instant/quick oats will not have to be physically broken down as much as regular oats.
2. Steaming will increase the GI to some degree (how much???)
3. MICROWAVING has bee shown to increase the GI's of foods moreso than that of those that have been boiled. An example of this can be seen in potatoes as well. Since most of us microwave our instant and quick oats, then this could also be a reason why they have a slightly higher GI rating than that of regular oats.
BMJ