When you are tired, your brain cells' ability to absorb glucose is highly diminished. As I explained in Secret #1, your brain's ability to control impulses is nil without glucose. What's worse, without enough sleep you are more likely to crave sugary snacks to compensate for low glucose levels. So, if you're trying to exert self-control over your eating, getting a good night's sleep-every night-is one of the best moves you can make.