Saint John Chrysostom on Fasting Before & After Communion
Before you have partaken, you fast, so that you may in a certain way appear worthy of Communion. But when you have partaken, when you should increase your temperance, you undo everything. And yet surely it is not the same to fast before and after it. For although it is our duty to be temperate at both times, it is particularly so after we have received the Bridegroom: before, so that you may become worthy of receiving; after, that you may not be found unworthy of what you have received.
"What then? Should we fast after receiving?" I am not saying this, nor do I use any compulsion. That would be good - but I do not enforce it. But I exhort you not to feast to excess.
(Homily 27 on I Corinthians, 7)