I didn't mean to imply that you can't increase willpower by managing blood sugar, but rather that the effect I described sets a limit on the total amount of benefit you can achieve this way. That is to say, while increasing your blood glucose from 80 to 100mg/dL is benefical for willpower, increasing it from 100 to 200mg/dL is disastrous. And most peoples' metabolism already maintains it at about the right point.