Catholics practice various acts of penitence and spiritual self-discipline during Lent, the (approximately) forty days leading up to Easter. One of those disciplines is a fast that requires Catholics to abstain from meat on Fridays during Lent. The rule is based on the authority of the Church, not on the authority of Scripture.
The rule that Catholics cannot eat meat on Fridays during Lent is actually more lenient than what most Catholics in history have had to observe. Centuries ago, the Catholic Church had a law that forbade consuming meat on all Wednesdays, Fridays, and Saturdays. Later, this rule was relaxed to remove meat from the diet on Ash Wednesday and all Fridays. In 1966, Catholic bishops in America, with the blessing of Pope Paul VI, further relaxed the rule. Nowadays meat is only prohibited on Ash Wednesday, Good Friday, and Fridays of the Lenten season. Catholics are obligated to observe this fast as a minimum; they can make up stricter requirements for themselves, if they so desire.
The stated reason for Catholics not being allowed to eat meat on Fridays during Lent is to remind the faithful that Jesus died on a Friday. Jesus gave up His body (His flesh), and Catholics, in an effort to attain greater communion with Christ, refrain from consuming flesh.
If there is no eating meat on Fridays, then why is eating fish allowed for Catholics? The United States Conference of Catholic Bishops states that fish are a different category of animal. So it’s only the meat of warm-blooded animals that is prohibited. Eggs, butter, and milk are also allowed.
There is nothing in the Bible that remotely suggests that Christians must follow a predetermined fast. Eating meat on Fridays or not eating meat on Fridays—or any other day—is not an intrinsically spiritual issue. Abstaining from meat during Lent is simply a man-made ritual of the Catholic Church. It has no inherent spiritual value and cannot guarantee that a person draws closer to Christ. While fasting can be beneficial, it is good to remember Jesus’ words, “What goes into someone’s mouth does not defile them” (Matthew 15:11).