Your metabolism is like a fire in the fireplace... feed it some manageable-sized logs every intermission, and you keep a good blaze going. Feed it nothing, and the fire goes out. Feed it too big a log, and the temperature goes down, takes too much energy for the fire to actually take on the log.
Same goes for your stomach and diet. 5-6 small meals (about the size of your fist) with good amount of water spread evenly throughout the day. Your metabolism gets used to the scheduled diet, and it acts accordingly to make room for more food. You'll notice more bowel movements this way.
If you feed it nothing, just like what these guys said, your system goes to preservation mode. Sensing that it doesn't know when it's going to get fed next, it preserves more of the food. You'll notice less bowel movements.
Feed yourself too much, and your digestion system won't be able to handle this. Self-explanatory. You only have to look at any 4 out of 10 Americans who suffer from obesity to see this.