Can. 1249 - All members of the Christian faithful in their own way are bound to do penance in virtue of divine law; in order that all may be joined in a common observance of penance, penitential days are prescribed in which the Christian faithful in a special way pray, exercise works of piety and charity, and deny themselves by fulfilling their responsibilities more faithfully and especially by observing fast and abstinence according to the norm of the following canons.
Can. 1250 - All Fridays through the year and the time of Lent are penitential days and times throughout the universal Church. [Although no particular penance is prescribed by the Church (ref. Can. 1250), the old discipline of abstinence on all Fridays and of fasting on all weekdays of Lent may be maintained. If not, it must be replaced by some other form of penance.]
Can. 1251 - Abstinence from eating meat or another food according to the prescriptions of the conference of bishops is to be observed on Fridays throughout the year unless they are solemnities; abstinence and fast are to be observed on Ash Wednesday and on the Friday of the Passion of the Death of Our Lord Jesus Christ. [Whenever a solemnity (first class feast) falls on a Friday, abstinence is dispensed.]
Can. 1252 - All persons who have completed their fourteenth year are bound by the law of abstinence; all adults are bound by the law of fast up to the beginning of their sixtieth year. Nevertheless, pastors and parents are to see to it that minors who are not bound by the law of fast and abstinence are educated in an authentic sense of penance.
Can. 1253 - It is for the conference of bishops to determine more precisely the observance of fast and abstinence and to substitute in whole or in part for fast and abstinence other forms of penance, especially works of charity and exercises of piety.
In England & Wales, such days include Ash Wednesday and all Fridays.
The law of abstinence requires a Catholic 14 years of age until death to abstain from eating meat on Fridays in honour of the Passion of Jesus on Good Friday. Meat is considered to be the flesh and organs of mammals and fowl. Moral theologians have traditionally considered this also to forbid soups or gravies made from them. Salt and freshwater species of fish, amphibians, reptiles and shellfish are permitted, as are animal-derived products such as gelatin, butter, cheese and eggs, which do not have any meat taste.
The law of fasting requires a Catholic from the 18th Birthday [Canon 97] to the 59th Birthday [i.e. the beginning of the 60th year, a year which will be completed on the 60th birthday] to reduce the amount of food eaten from normal. The Church defines this as one meal a day, and two smaller meals which if added together would not exceed the main meal in quantity. Such fasting is obligatory on Ash Wednesday and Good Friday. The fast is broken by eating between meals and by drinks which could be considered food (milk shakes, but not milk). Alcoholic beverages do not break the fast; however, they seem contrary to the spirit of doing penance.
Those who are excused from fast or abstinence, besides those outside the age limits, those of unsound mind, the sick, the frail, pregnant or nursing women according to need for meat or nourishment, manual laborers according to need, guests at a meal who cannot excuse themselves without giving great offense or causing enmity and other situations of moral or physical impossibility to observe the penitential discipline.