Why Does Fasting Make You More Alert?

On the show, being fasted increases alertness because fasting puts high levels of epinephrine in the system. People always think that going without food will leave them tired. Energy from food is used from glycogen after a long storage and conversion process, and the food itself consumes energy to digest. A lot of people feel better fasted.

The comparison is fasting or being thirsty before exhaustion arrives. The show says people presumably fasted for long periods throughout history and still had to stay up for two or three days. If a family member is sick, staying awake in the hospital can happen without any trouble. The alertness system is all mental.