The church historian Socrates Scholasticus talks about the different customs of fasting already back in the fourth century. Even today, when the Church generally follows the same rules everywhere, there are many local variations. The calendar that my church puts out is different in many respects from the calendar put out by the Russian church I used to attend. For instance, during the Apostles' Fast we are permitted fish every day but Wednesday and Friday; other places say fish is only permitted on Saturdays and Sundays. On the other hand, we do not eat oil on Wednesday and Friday during the Pentecostarion, but other churches say it is permitted; we are permitted cheese and eggs on the Wednesday before Ascension, others say it is forbidden and only fish is allowed. Many individuals in my church only fast from oil during the first week of Lent and Holy Week, while others keep the strict fast throughout the forty days. Socrates explains the great variation in his day as the result of no apostolic directives on the manner of fasting; the principle was rather that each Christian should fast according to his own strength.
It is true that you can find sources that appear to lay down a more uniform practice. St Nicodemus of the Holy Mountain says not only that the Fathers forbid oil and wine on Wednesday and Friday and during Great Lent, but also that on those days we are to abstain from all food and drink until the ninth hour, and then only eat dry foods. But how many keep it this strictly, except perhaps on Great Friday or the Exaltation? What may have been the norm in St Nicodemus' time is not necessarily how we should do things now. The right way to fast is to obey the instructions of your spiritual father, and not to exceed what he lays down for you without his blessing, and finally not to pay any attention to how others fast or to talk unnecessarily about your own fasting.