It’s supposed to symbolize that the Body of Christ feeds you physically as well as spiritually. If you go right after a heavy meal you don’t have any physical hunger.
I believe that before Vatican II, the rule was no food after the previous midnight before receiving the Eucharist. I don’t think there were too many vigil Masses back then.
DISCLAIMER: Catholic Answers has turned over the archive to Catholic-Questions.org and no longer owns, manages, or moderates the forums. For additional apologetics resources please visit www.catholic.com.