§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.
§2. A priest who celebrates the Most Holy Eucharist two or three times on the same day can take something before the second or third celebration even if there is less than one hour between them.
§3. The elderly, the infirm, and those who care for them can receive the Most Holy Eucharist even if they have eaten something within the preceding hour.
Source: Code of Canon Law (Vatican.va)