Unfortunately, in their eyes this is good advice. If you are really serious about reversing it, buy yourself a Glucose monitor and start testing the foods you eat. Test before your first mouthful, and 2 hours after. If the rise is more than 2mmol, something in the meal had to many Carbs for your body to handle, ie Potatoes, Pasta, Bread, Rice and Cereals. Then try eliminating or reducing these items until you get an acceptable rise. Eventually you will learn what YOUR body can tolerate, and what to avoid. At this point your testing will drop off as you will know if a meal works for you.
I think that at the Prediabetic stage is when the medical profession should really push the advice as this is when it is easiest to stop type 2 developing. As prediabetic it should not take any radical alterations, but subtle changes should have a very good impact.
If you cut out Carbs you must replace them with either protein or fat. ( DO NOT be scared of natural fats, forget EVERYTHING you've ever been told or heard about what they will do to you. they WON'T).