The rule of fasting, which is dependent on the Church's cycle of feasts and fasts, is contained in the Church's Typicon chiefly in Chapters 32 and 33. In general, fast days for Orthodox Christians are all Wednesdays and Fridays throughout the year (except for fast free periods), the 4 canonical fast periods of Great Lent, Nativity Fast, Apostle's Fast, and Dormition Fast, and a few special days: the Exaltation of the Cross (sept. 14th) and the Beheading of the Forerunner (Aug. 29th) - which, even though they are feast days, are also fast days (with wine and oil allowed) for the sake of the events commemorated thereon.
There are some local variations in the allowances of wine and oil, and sometimes the fish, and so the indications in the present Calendar cannot be uniformly applied everywhere. For one who has become accustomed to the Orthodox fast, the allowance of oil on food or fried foods togeter with a little wine is indeed a consolation as well as a source of physical strength. While the Typicon itself indicates 2 variant practices (as for a few of the weekdays of Great Lent), the present Calendar follows the Typicon's preferred practice.
While most Orthodox Christians are perhaps aware of the general rule of fasting for Great Lent and the Dormition Fast (wine and oil allowed only on Saturdays and Sundays, except for a few fast days and vigils), many are probably not familiar with the precise rule governing the less severe fast of the Nativity and Apostle's Fast.
In these 2 fasts, the fast for laymen is the same as that of many Orthodox monasteries, where Monday throughout the year is kept as a fast day in honor of the fleshless ones, the Angels.
This rule of fasting is not intended to be a "straight-jacket" for Orthodox believers, not a source of pharisaical pride for anyone who keeps the letter of the Church's law. It is the rule, the standard, against which each is to measure his own practice, and towards whch one must always strive, according to one's strength and circumstances. Whenever, for sickness or any other reason, one falls shrt of the rule, he applies to himself the spiritual medicine of self-reproach ad strives to enter more fully into the spirit nd discipline of fasting, which is indeed of great spritual benefit to those who sincerely strive to follow it.