If I have a full meal I barely can stay awake. I know that the body switches into a different mode to process the meal and extract the proteins etc and for this it drains me of other energy like focusing. It is interesting how my productivity increases with hunger. That's why lions sleep 20 hours a day. After a massive meal they can barely do anything but digest. So I think mammals' first thing of the day is to go out and find food. Once food found and eaten there's no point to stay awake. I really think that a meal concludes the day not starts it in the animal world. Although providing the body with just enough to keep it fueled and in a way that it won't have to put you to sleep to extract the proteins we can make ourselves do more and take hunger & sleeping off our minds during the day.

To stay fresh just don't starve or over-eat yourselves. It works for me.