SB is an excellent plan for prediabetes-- it goes right to the core issues that are involved with it, so it would not cause prediabetes unless followed incorrectly. It is more likely that you already had the other markers for it from previous ways of eating, but were never tested for the markers because your fasting blood sugar was fine.
The list of criteria in the main SB book (p. 76-7) is as follows:
- High cholesterol
- High ratio of bad cholesterol to good
- High blood pressure
- Central obesity
- High triglycerides
To which I would add (that's still Dr A talking):
- Small LDL (bad cholesterol) particles
Notice that high blood sugar isn't on the list. Prediabetes is associated with the indicators where your body is being set up for the possibility of repeated high blood sugar in the very near future. It can be reversed with a good diet (like SB), plus exercise helps a lot as well.
I wouldn't be in favor of drinking something high GI that helps further the prediabetes risks. Some doctors are used to that old school test, so a second opinion is a good idea. If they are following the newer indicators, they can test your blood for the things above (although I believe the book says the particle size test is expensive) instead.
Another good test is the glycosylated hemoglobin (HgA1C), which looks at an average blood sugar reading over the last few months. Dr Sears of The Zone also suggests getting a fasting insulin test.
That's the research side of things, so now for the personal side. I was also warned of prediabetes by my doctor, but I was in denial and didn't pay attention. It got worse and worse with my US pyramid eating, and then I discovered SB. After losing something like 60 pounds, I was back to a similar weight as when my doc warned me of prediabetes, but this time my bloodwork was good. She said to keep doing what I was doing, and that SB is a great diet (she wished that she had written the book).
I'm not sure why you aren't eating grains if you're on SB, though. We should eat them-- we just need to watch the types and portions very carefully. It is based on good carbs, good fats, and lean proteins. Do you have the book? What does a typical day's SB menu look like for you?
Compared to other suggested cereals, the SB brand cereal is not that great of a choice. Old-fashioned oatmeal is a much better choice. Uncle Sam is a great choice if you want a cold cereal.