No monk [Christian] became holy without ascetic exercises. No one can ascend to spirituality without exercising himself. These things must be done. Ascetic exercises are such things as prostrations, vigils and so on, but done without force. All are done with joy. What is important is not the prostrations we will make or the prayers, but the act of self-giving, the passionate love for Christ and for spiritual things. There are many people who do these things, not for God, but for the sake of exercise, in order to reap physical benefit. But spiritual people do them in order to reap spiritual benefit; they do them for God. At the same time, however, the body is greatly benefited and doesn’t fall ill. Many good things flow from them.
Among the various ascetic exercises, prostrations, vigils and other deprivations, is fasting. "A fat belly does not make for a refined mind", as I know the Fathers like to say! All the books of the Fathers speak of fasting. They emphasize that we should not eat foods that are difficult to digest, or that are rich and fatty, because they are bad for the body and for the soul. They say that a lamb eats only grass and that is why it is so placid. That’s why we say someone is like a lamb. The dog or cat and all the carnivorous animals are all fierce animals. Meat is bad for people. Fruit and vegetables are good. That’s why the Fathers speak about fasting and condemn overeating and the pleasure one feels when one eats rich foods. Let our food be more simple, and let’s not occupy ourselves so much with it.
It is not food or good conditions in life that secure good health. It is a saintly life, the life of Christ. I know hermits who fasted with the greatest austerity and were never ill. You’re not in danger of coming to any harm by fasting. No one has become ill by fasting. People who eat meat and eggs and milk-products are much more likely to become ill than those who adopt a meagre diet. This is an established fact and endorsed by medical science. Indeed, this is what doctors recommend. Not only do those who fast not come to any harm, but they are cured of illnesses.
To do this, however, you need to have faith. Otherwise you will feel empty and nauseous and have a craving for food. Fasting is also a matter of faith. It does you no harm when you digest your food properly. The hermits transform air into albumen and fasting doesn’t affect them. When you have love for things divine, you can fast with pleasure and everything is easy; otherwise everything would seem impossibly difficult. All those who have given their heart to Christ and pray with fervent love have managed to overcome and control their craving for food and lack of continence.
There are many people today who were unable to fast for a single day and now live as vegetarians, not for religious reasons, but simply because they believed it would be good for their health. But you have to believe that you won’t come to any harm by not eating meat.
From the book Wounded by Love: the Life and Wisdom of Elder Porphyrios.