Good Friday is an obligatory day of fasting and abstinence for Catholics.
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, as well as two smaller meals that together are not equal to a full meal. The norms concerning abstinence from meat are binding upon members of the Latin Catholic Church from age 14 onward.
Members of the Eastern Catholic Churches are to observe the particular law of their own sui iuris Church.
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.
More information on fasting and abstinence can be found here.