“Question from [a monk, who was also a priest, in the community of Seridos] to the Other Old Man (John): When I give to my body more than is necessary, it does not help me during the Liturgy; and if I give it less, I am afraid it will collapse completely. What should I do about this? And in regard to Holy Communion, since I want to partake of this every day, is it a burden to me that I approach Holy Communion as a sinner or should I continue to partake of it? And, again, how can I protect my life in silence?
Response by John
I have previously mentioned to your love, Abba, the words of John to the Savior; and yet you have written once again to me, the foolish and ignorant one. Therefore, if John [the Baptist] had then refused to respond, what can I who am disdained now respond? So I am speaking the truth when I say I am nothing and that I know nothing. Yet for the sake of obedience, I speak that which I have in my heart. However, I will not say it is exactly like this, but I am speaking according to what I am. God does not demand from the one who is ill any physical function, but only a spiritual function, namely prayer. For it is said, “pray without ceasing” (1 Thess 5:17).
As for bodily diet, if the body cannot perform the Liturgy when it receives sufficient food, and if you are afraid of illness when it receives insufficient food, then keep to the middle way. Give it neither too much nor too little. Then the scripture is fulfilled, which says: “Deviate neither to the right nor to the left” (Num 20:17). But give the body just a little less than it requires. For this is the way of the fathers: neither to be wasteful nor to be crushed in one’s discipline. As for approaching Holy Communion, when this happens to you not out of ignorance but because of illness, then there is no condemnation. For the greatest physician goes himself to those who suffer greatly and are ill, just as our Lord Jesus himself came to us sinful and sick people. Forgive me, father, but I the unworthy one have spoken out of obedience.”
Barsanuphius & John, Letters from the Desert, Letter 212.