“Besides eating rarely, Fasting also means not eating much. Apart from eating once a day, one should also limit the quantities of the consumed food. Waiting for a certain hour to indulge in an insatiable enjoyment both in body and in mind is an unreasonable way to observe a fast.
In reasoning about food, one must also observe that he should not distinguish between tasty and tasteless food. This business, characteristic of animals, is below a reasonable person. We refuse to take pleasure in food in order to subdue the warring members of the flesh and give freedom to the actions of the spirit.
True fasting consists not only in the exhaustion of the flesh, but also in giving the much desired part of your daily bread to the hungry: “Blessed are those who hunger and thirst […], for they will be filled” (Matt. 5:6).
Our Savior, the Lord Jesus Christ, before setting out on His mission of the redemption of the human race, strengthened Himself with a long fast. Similarly, all the ascetics, prior to serving the Lord, armed themselves with fasting and entered the path of the Cross in no way other than the feat of fasting. They measured their success in asceticism by their success in fasting.
Saints did not begin strict fasting without due preparation. Slowly and steadily, they trained their ability to be content with the most meager food. The Venerable Dorotheos, training his disciple Dositheos in fasting, gradually limited his meals, finally reducing the measure of his daily food from four pounds to eight lots of bread.
At the same time, the holy fasters surprised others with their tirelessness, good cheer, strength and readiness to work. Diseases were rare among them, and they lived extremely long lives.
While the flesh of the fasting person becomes thin and light, his spiritual life comes to perfection and opens itself to miraculous manifestations. The spirit then performs his actions in what appears to be an incorporeal body. At this point, the external senses seem to go numb, and the mind renounces the earth, ascending to Heaven and becoming completely immersed in the contemplation of the spiritual world.
However, not everyone will be able to impose on himself a strict rule of abstinence in everything or deprive himself of everything that serves to alleviate infirmities. “Let anyone accept this who can”(Mt. 19:12).
Not everyone can “accept” imposing on himself a strict rule of abstinence in everything or depriving himself of the things that ease his weaknesses.
Enough food should be consumed every day to strengthen the body, a friend and helper of the soul in the accomplishment of virtue. Otherwise, the exhausted body may also weaken the soul. On Fridays and Wednesdays, especially during the four fasts, eat food once a day, following the example of the fathers. Seeing that, the Angel of the Lord will cling to you.
Source: Venerable Seraphim (Moshnin) of Sarov. Spiritual Instructions to Monastics and Laity