Catholics are only required to fast during Lent on Ash Wednesday and Good Friday, and they are required to abstain from meat on each Friday during Lent. Many Catholics abstain from additional pleasures or indulgences either during Fridays or the entire Lenten period, but the Church does not require this.
The fasts on Good Friday and Ash Wednesday are not total abstentions from eating. Catholics are allowed to eat a single full meal over the course of the day. They can eat this either as a single meal or spread out the same amount of food throughout the day. However, as with all Friday meals during Lent, the meals taken on Good Friday and Ash Wednesday must be meatless.
In terms of Catholicism, meatless means food not made from an animal that lives on land. Therefore, fish and shellfish are not considered meat for the purposes of Lenten fasting. While fish and shellfish are allowed during Fridays and fast days, Catholics should keep the reason for the fast in mind and avoid overindulging in these foods.
All able-bodied Catholics must participate in Lenten fasting, but certain individuals are exempt from this requirement. Children under 18 years of age, the elderly, the mentally ill, those with health problems and pregnant or nursing women are not required to participate in Lenten fasting.