Rice, hard wheat, and noodles all have something in common. They have what is called a high 'glycemic index'. That is the 'octane' of a given food. Glycemic index is the speed at which any given food will metabolize into sugar in the blood. People with blood sugar problems have compromised abilities to manage high blood sugar, so, for them low glycemic index foods are healthier.
We don't have to concern ourselves with meat or oils, only those foods with carbohydrates. That is fruits, some nuts (like chestnuts), some beans (legumes), but mostly grains. Since grains make a large % of preppers stored food, this must be addressed.
If a person is a type 1 diabetic, until such time as we learn to regenerate the pancreas, they will need insulin to survive. In a grid-down situation, sourcing insulin may be a challenge, so it would be wise to make what you have last as long as possible. If you eat low glycemic foods, you can make your insulin stores last longer.