"Ash Wednesday and Good Friday are obligatory days of fasting and abstinence for Catholics. In addition, Fridays during Lent are obligatory days of abstinence.
For members of the Latin Catholic Church, the norms on fasting are obligatory from age 18 until age 59. When fasting, a person is permitted to eat one full meal. Two smaller meals may also be taken, but not to equal a full meal. The norms concerning abstinence from meat are binding upon members of the Latin Catholic Church from age 14 onwards.
If possible, the fast on Good Friday is continued until the Easter Vigil (on Holy Saturday night) as the "paschal fast" to honor the suffering and death of the Lord Jesus, and to prepare ourselves to share more fully and to celebrate more readily his Resurrection." USCCB website
Fasting in the East, Byzantine or Orthodox, will differ according to the sui juris churches, but here is what is usually suggested:
"Week before Lent ("Cheesefare Week"): Meat and other animal products are prohibited, but eggs and dairy products are permitted, even on Wednesday and Friday.
First Week of Lent: Only two full meals are eaten during the first five days, on Wednesday and Friday after the Presanctified Liturgy. Nothing is eaten from Monday morning until Wednesday evening, the longest time without food in the Church year. (Few laymen keep these rules in their fullness). For the Wednesday and Friday meals, as for all weekdays in Lent, meat and animal products, fish, dairy products, wine and oil are avoided. On Saturday of the first week, the usual rule for Lenten Saturdays begins (see below).
Weekdays in the Second through Sixth Weeks: The strict fasting rule is kept every day: avoidance of meat, meat products, fish, eggs, dairy, wine and oil.
Saturdays and Sundays in the Second through Sixth Weeks: Wine and oil are permitted; otherwise the strict fasting rule is kept.
Holy Week: The Thursday evening meal is ideally the last meal taken until Pascha. At this meal, wine and oil are permitted. The Fast of Great and Holy Friday is the strictest fast day of the year: even those who have not kept a strict Lenten fast are strongly urged not to eat on this day. After St. Basil's Liturgy on Holy Saturday, a little wine and fruit may be taken for sustenance. The fast is sometimes broken on Saturday night after Resurrection Matins, or, at the latest, after the Divine Liturgy on Pascha.
Wine and oil are permitted on several feast days if they fall on a weekday during Lent. Consult your parish calendar. On Annunciation and Palm Sunday, fish is also permitted." Abba Moses website....graphic below found at St Sophia's website- explore their great fasting/abstaining reflections
Smugness abounds, even when both East and West try not to be. The East looks at the West and scoffs- they call that a fast? The West looks at the East and smirks- really, they are either eating ribeyes in secret, they force their children to be schema-monks, or they are going to make themselves sick with all that soy.
I find myself in the middle. For fasting times, we are meatless except Sundays and vegan on Wednesdays and Fridays. It is easier to be Roman-rite where fasting is concerned. Excepting health reasons, the fast is clear. It is not that difficult, but everybody (with some exceptions) does it. Even McDonald's has fish sandwiches on sale on Fridays!
If you take a look at the Orthodox/Byzantine fasting guidelines (they don't call them requirements....everyone does what they can....which drives me crazy because people pretend to be all flexible but then they are scandalized when you eat fish in a Sunday in Great Lent), we cannot eat a fish sandwich even on Sundays! There is cheese, mayonnaise, no vegan items- and to top it all off- fish is not allowed except for Annunciation and Palm Sunday!
Theologians- explain this to me. We Easterners do not 'bury the alleluia' during Great Lent and we continue to stand during the consecration because 'every Sunday is a little Easter Sunday.' So why is fish not permitted on a 'little Easter Sunday?' I am growing in my fasting prowess, but I am not convinced that it is even proper to fast and abstain on any Sunday. Convince me.