Question: According to the Church's Code of Canon Law, are we supposed to fast for an hour before Mass begins, or for an hour before we receive Communion?
Answer: (Canon 919.1) A person who is to receive the Most Holy Eucharist is to abstain for at least one hour before holy communion from any food and drink, except for only water and medicine.
Learn more:
http://catholicism.about.com/od/thesacraments/f/What-Are-The-Rules-For-Fasting-Before-Communion.htm