The first key remaining question in this experiment is: would I get the same 50-some point spike in blood sugar if I ate shredded wheat at noon instead of at 7:30 am? Data show some obvious glucose release by the liver during the night which puts my level typically in the high 90s on waking, so a 50-point spike at breakfast means I hit almost 150. But my waking value is more than 20 points above my low for the day which hovers in the mid-70s.
If I got less than a 50-point spike, then it could be that the liver was shutting down any remaining glucose output so as to blunt the effect of a midday intake of carbs. If I got more than a 50-point spike, then it could be that the liver becomes more active in order to push my peak sugar to some set level - the total spike would have to be about 75 points to hit my morning peak of 150. Or maybe the liver can release other substances into the bloodstream or the digestive tract to control how much carbohydrate is broken down into glucose and absorbed into the bloodstream. Carbs are digested into glucose in the small intestine (the more refined, the higher in the intestine); they get absorbed as sugars.
The answer turns out to be that I got the very same 50-point spike from the cereal at noon as at 7:30 am. I measured 74 at noon, just before eating. Then I ate the cereal, waited until 1 pm, and measured 124. There's your 50 points.
This suggests that the liver releases glucose from its stored glycogen on its own schedule, regardless of food intake. I'm assuming here that glycogen breakdown is the mechanism active overnight and for a couple hours after I wake up. The liver has another mechanism, gluconeogenesis, in which glucose is made from non-carbs, but it's my understanding that doesn't become active until your glycogen stores are gone. Despite my zero-sugar experimental diet, I think I'm still taking in enough total carbs to keep my glycogen stores nonzero.