"The Apostles almost always fasted."
Saint John Chrysostom (Sermon 57 on the Gospel of Matthew)
Patristic Testimony Concerning the Fast
The fast of the holy Apostles is very ancient, dating back to the first centuries of Christianity. We have the testimony of St. Athanasius the Great, St. Ambrose of Milan, St. Leo the Great and Theodoret of Cyrrhus regarding it. The oldest testimony regarding the Apostles Fast is given to us by St. Athanasius the Great (†373). In his letter to Emperor Constance, in speaking of the persecution by the Arians, he writes: "During the week following Pentecost, the people who observed the fast went out to the cemetery to pray." "The Lord so ordained it," says St. Ambrose (†397), "that as we have participated in his sufferings during the Forty Days, so we should also rejoice in his Resurrection during the season of Pentecost. We do not fast during the season of Pentecost, since our Lord Himself was present amongst us during those days … Christ’s presence was like nourishing food for the Christians. So too, during Pentecost, we feed on the Lord who is present among us. On the days following his ascension into heaven, however, we again fast" (Sermon 61). St. Ambrose basis this practice on the words of Jesus concerning his disciples in the Gospel of Matthew 9:14, 15: "Can the wedding guests mourn as long as the bridegroom is with them? The days will come, when the bridegroom is taken away from them, and then they will fast.”
St. Leo the Great (†461) says: "After the long feast of Pentecost, fasting is especially necessary to purify our thoughts and render us worthy to receive the Gifts of the Holy Spirit ... Therefore, the salutary custom was established of fasting after the joyful days during which we celebrated the resurrection and ascension of our Lord, and the coming of the Holy Spirit.''
The pilgrim Egeria in her Diary (fourth century) records that on the day following the feast of Pentecost, a period of fasting began. The Apostolic Constitutions, a work no later than the fourth century, prescribes: "After the feast of Pentecost, celebrate one week, then observe a fast, for justice demands rejoicing after the reception of the gifts of God and lasting after the body has been refreshed."
From the testimonies of the fourth century we ascertain that in Alexandria, Jerusalem and Antioch the fast of the holy Apostles was connected with Pentecost and not with the feast of the Apostles Peter and Paul on June 29. In the first centuries, after Pentecost there was one week of rejoicing, that is Privileged Days, followed by about one week of fasting.
The canons of Nicephoros, Patriarch of Constantinople (806-816), mention the Apostle's Fast. The Typicon of St. Theodore the Studite for the Monastery of Studios in Constantinople speaks of the Forty Days Fast of the holy Apostles. St. Symeon of Thessalonica (†1429) explains the purpose of this fast in this manner: "The Fast of the Apostles is justly established in their honor, for through them we have received numerous benefits and for us they are exemplars and teachers of the fast ... For one week after the descent of the Holy Spirit, in accordance with the Apostolic Constitution composed by Clement, we celebrate, and then during the following week, we fast in honor of the Apostles."
Duration of the Fast
The Fast of the Apostles came into practice in the Church through custom rather than law. For this reason there was no uniformity for a long time, either in its observance or its duration. Some fasted twelve days, others six, still others four, and others only one day. Theodore Balsamon, Patriarch of Antioch (†1204), regarding the Apostle's Fast, said: "All the faithful, that is the laity and the monks, are obliged to fast seven days and more, and whoever refuses to do so, let him be excommunicated from the Christian community."
From the work On Three Forty Days Fasts, which is credited to a monk of the monastic community of St. Anastasios the Sinaite (6th or 7th century), we learn that the Fast of the holy Apostles lasted from the first Sunday after Pentecost to the feast of the Dormition of the Most Holy Mother of God on August 15. Later, however, the Fast of the Dormition was separated from it and the month of July was excluded from the Fast of the Apostles. St. Symeon of Thessalonica speaks of the Apostle's Fast as of one week's duration.
In the Orthodox Church the Fast of the holy Apostles lasts from the day after the Sunday of All Saints to the 29th of June, the feast of the Apostles Peter and Paul. This fast may be of longer or shorter duration depending upon which day Pascha is celebrated. According to the Old Calendar it could last from as little as 8 days to as many as 42 days depending on the date of Pascha, but this is shortened by the New Calendar which sometimes obliterates the Fast altogether. If the feast of Pascha occurs sooner, then the Apostle's Fast is longer; if Pascha comes later, then the Apostle's Fast is shorter.
Prescription For the Fast
The Fast of the Apostles is somewhat more lenient than the Great Fast before Holy Week and Pascha. The Kievan Metropolitan George (1069-1072) approved the Rule for the Kiev Caves Monastery which does not allow meat or dairy products to be eaten during the Apostle's Fast. On Wednesday and Friday, they prescribed dry food, that is, bread and water or dry fruits. On Tuesday, Thursday, Saturday and Sunday they permitted fish, wine and oil. In addition to this, they directed that one hundred prostrations (profound bows to the ground) be made daily, excepting Saturdays, Sundays and holy days (the Feast of the Birth of John the Baptist falls on June 23rd and fish, oil and wine is permitted no matter the day). This rule was transferred to Russia via the Kiev Caves Monastery who based their rule on that of the Monastery of Studios in Constantinople. We can thus assume this was the rule for the Fast practiced by both the Roman Empire and the Russian Empire. This is the rule still practiced today with possible minor variations among jurisdictions.