blood sugar is mostly regulated by hormones: glucagon and insulin. Not really by what you just ate. Hence why you can go days without eating and still have a normal blood sugar. Eating causes your pancreatic beta cells to release insulin (in response to elevations in blood glucose). Diabetics have spikes in their blood sugar right after they eat because they have impaired insulin sensitivity and so their tissues (muscles mainly) don't take up the sugar in the blood (a process mediated by insulin receptors).