Hi Talos,
When you have an HBA1c done it is an average of your blood sugars over the last 120 days.
Average is just that and so it does not chart when you have highs and lows. Some foods give you what is called the pizza effect. This means that they could spike later than the 2hrs. you are testing. In your case, the shredded wheat MAY be spiking you later than the 2hrs. We all need to keep our blood sugars steady and try to get them as near as possible to the reading taken before we had a meal. If, for example, every time you eat the shredded wheat you are peaking 3 - 4 hours later then your high blood sugars are not seen by you and long term can cause damage.
(5.6 before meal, 5.9 when measured 2hrs later but MAYBE 8.9. or even 10 later. If this was the case then you are having a 10 every time from the shredded wheat. Imagine how that would look on a graph.) That is why it is essential to do later tests when getting to grips with foods that are suitable for you in the beginning.
I found this problem with potatoes early on.
The main issue with all of us when new to this is the provision of test strips. Your HBA1c may be acceptable but nobody is aware of what is actually happening on a daily basis if they cannot test.
Ideally your blood sugars should even out after eating within 2 hours.
Hope this helps,
Catherine.