Unless you shall do penance, you shall all likewise perish - Luke 13:3
The fasting laws of the Catholic Church can get a little confusing at times, so, with Lent approaching, I wanted to put them up here for you, from the Code of Canon Law.
The Baltimore Catechism explains a fast day as one on which only one full meal is allowed, but in the morning and evening some food may be taken, the quantity and quality to be determined by local custom. That quantity is currently explained as the two snacks should not equal one full meal, meaning you get to eat one meal a day, with two snacks for sustenance.
Can. 1249 All Christ's faithful are obliged by divine law, each in his or her own way, to do penance. However, so that all may be joined together in a certain common practice of penance, days of penance are prescribed. On these days the faithful are in a special manner to devote themselves to prayer, to engage in works of piety and charity, and to deny themselves, by fulfilling their obligations more faithfully and especially by observing the fast and abstinence which the following canons prescribe.
Can. 1251 Abstinence from meat, or from some other food as determined by the Episcopal Conference, is to be observed on all Fridays, unless a solemnity should fall on a Friday. Abstinence and fasting are to be observed on Ash Wednesday and Good Friday.
Can. 1252 The law of abstinence binds those who have completed their fourteenth year. The law of fasting binds those who have attained their majority, until the beginning of their sixtieth year. Pastors of souls and parents are to ensure that even those who by reason of their age are not bound by the law of fasting and abstinence, are taught the true meaning of penance.
Can. 1253 The Episcopal Conference can determine more particular ways in which fasting and abstinence are to be observed. In place of abstinence or fasting it can substitute, in whole or in part, other forms of penance, especially works of charity and exercises of piety.