It is important to understand what happens inside the body when you eat... especially carbs.
Basically, you eat a fast-absorbing carb (simple carb, like table sugar), and it hits the blood stream quickly. The sugar in your blood goes up, too high. The body sends insulin out to force the sugar into the cells, because too much sugar in the blood is dangerous, but it is safe in the cells.
But now the body might have sent too much insulin, and now your blood sugar is low. Normally adrenaline kicks in about this time to go release some sugar back into the blood. But for some people this mechanism is damaged, so the blood sugar drops and the body can't increase it on its own. So, you have to eat more carbohydrate.
The way to fix this vicious cycle is to always eat carbs with protein and fat which slows their entry into the bloodstream, and concentrate on eating complex carbs that also enter more slowly.
This is what the glycemic index is about. The lower the #, the slower the sugars hit the bloodstream. Anyone with poor blood sugar control should only consume carbs #54 and less. (As a starting point. Individual results vary).