The Code of Canon Law
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.
Catechism of the Catholic Church
1387 - To prepare for worthy reception of this sacrament, the faithful should observe the fast required in their Church.220 Bodily demeanor (gestures, clothing) ought to convey the respect, solemnity, and joy of this moment when Christ becomes our guest.
220 Cf. CIC, can. 919