Secreting insulin is the mechanism that keeps blood sugar down, which is only half the job of homeostasis. The other half is keeping blood sugar up when you haven't eaten a bunch of carbs recently, and it seems (anecdotally) that if people don't exercise that second half -- i.e., if they keep their blood sugar up by eating constantly -- that their body's ability to keep blood sugar up on its own atrophies.
When your body's blood sugar regulation is working properly, you can skip one or two meals without any dire consequences(+). You have a bunch of glycogen in your muscles and liver, for one thing, and your body just has to release that energy into your bloodstream as glucose. It's really that simple, but the impression I get from a lot of people is that their blood sugar regulation is only half-working. They take it for granted that if they miss lunch, they're going to be a wreck in the afternoon. They become tired and irritable, and they may even have headaches. That shouldn't be considered normal. A sugar crash isn't a normal reaction to a brief interruption of a healthy diet; it's a warning sign that your diet before the crash was not healthy.
(+) I won't swear this holds true if you exercise intensely, since I haven't tried it, but the paleo lifestyle guys say they have no problem exercising on their "lean" days.
I won't swear this holds true if you exercise intensely, since I haven't tried it, but the paleo lifestyle guys say they have no problem exercising on their "lean" days.
I don't have any problems having a rather intensive strenght training session after about 16 hours without food, and my performance does not seem to suffer. I didn't try anything more extreme than that (yet).
I was under the impression that a sugar crash is the result of your body maintaining your blood sugar on it's own[0].
[0] On it's own, meaning secreting insulin from the pancreas to maintain homeostasis.