When I was reading the New York Times the other day I came across this question and I have a slightly different opinion than the printed response. We eat and drink during the day for activity. At night we utilize the foods we consumed during the day to maintain and rebuild our bodies. While we are sleeping our bodies are cleaning, maintaining and repairing themselves and gathering physical and energetic excess to be eliminated in the morning when we rise. Most people have their morning routine which usually consists of going to the bathroom, washing, brushing our teeth, doing a body rub and stretching. All of these practices help eliminate the excess we gathered during the night.
Our organs, brain and nervous system also recharge at night during sleep. Our need for sleep is determined by how efficiently our bodies can clean, repair, recharge and eliminate. The length of our sleep also determines how refreshed we feel from our sleep. We get the deepest and most refreshing sleep between midnight and 4 am. Going to sleep before midnight is important so that we can be in a deep sleep during these hours. It is hard to feel refreshed the next day when we go to sleep after midnight.
A healthy person generally needs between five and eight hours of sleep per night. Stimulants like coffee or alcohol as well as eating before sleep can increase our need for sleep. Through adjusting our daily habits, diet and activity we can get the deepest, most refreshing sleep in the shortest amount of time.