The past couple of days, after lunch, my blood sugar spiked and crashed. Not to unsafe levels, mind you, but enough that I got really tired when my blood sugar crashed back down.
Yesterday, I noticed it as I was sitting in a presentation at work after lunch and I needed help staying awake. Because I made some not wise dietary choices—having some sushi, which includes rice—I actually checked my blood sugar two hours after lunch. Sure enough: my blood sugar was higher than I expected. When I checked an hour later, it dropped 30 mg/dl.
Today, I had a similar experience. This time it wasn't due to my breakfast or my lunch choices, which were fairly low carb. But I'm guessing it's something that was in the trail mix I had been eating at the office the past couple of days: Raisins. The amount of raisins I ate over the past couple of days was not terribly excessive (1-2oz a day), but clearly it was enough to spike my blood sugar.
A quick look on the Internet suggests raisins both have a high glycemic index and a glycemic load, the latter of which is more important in that it helps determine how quickly the sugars will hit your system.
Just to give an example based on recent dietary choices: An apple has a glycemic index of 36-40, but a glycemic load of 6. Meanwhile, raisins have a glycemic index of 53-75 and a glycemic load of 28. Rice is similar to raisins in this regard.
Bottom line: I need to avoid things that I know will spike my blood sugar.