Lent is a 40 day season of prayer, fasting, and almsgiving that begins on Ash Wednesday and ends at sundown on Holy Thursday. It's a period of preparation to celebrate the Lord's Resurrection at Easter. During Lent, we seek the Lord in prayer by reading Sacred Scripture; we serve by giving alms; and we practice self-control through fasting. We are called not only to abstain from luxuries during Lent, but to a true inner conversion of heart as we seek to follow Christ's will more faithfully. We recall the waters of baptism in which we were also baptized into Christ's death, died to sin and evil, and began new life in Christ.
Catholics age 14 and older do not eat meat on Ash Wednesday and all Fridays during Lent, including Good Friday. Instead of meat many Catholics choose to eat fish - which is why many parishes around the country have fish fries on Fridays during Lent. These are a great opportunity for a parish community to come together to pray and fast.
On Ash Wednesday and Good Friday, Catholics age 18 to 59 also limit the amount of food they eat. Only one full meal, and two smaller meals that together do not equal a full meal, are eaten. The best rule of thumb is to make sure your meals are smaller than what you would eat on a normal day - and to avoid snacks. Exemption is allowed for pregnant women and those who need regular meals for medical reasons.
You may have heard the words "fasting” and “abstinence" used when talking about Lent. “Fasting” is the word used when the amount of food eaten is limited. “Abstinence” is when you completely give something up, like meat, for a set period of time. Both "fasting" and "abstinence" play a role during Lent.
The Church has some very clear guidelines for how we should incorporate fasting as a Lenten observance. The how is simple, but what about the why? Fasting without the why is pointless.
The purpose of fasting is to turn back to God. Missing that primary purpose makes fasting fruitless. Sure, fasting has become a popular secular practice for everything from medical treatments to weight loss, but these uses are secondary.
Fasting is a sharp reminder that there are more important things in life than food. Lenten fasting helps to release us from our attachments to the things of this world. It is often these worldly attachments that prevent us from becoming the-best-version-of-ourselves. Fasting also serves as a reminder that everything in this world is passing.
Go without food for several hours and you quickly realize how truly weak, fragile, and dependent we humans are. This knowledge strips away arrogance and fosters a loving acknowledgement of our utter dependence on God.
It is important to remember that fasting is primarily a spiritual exercise. We do not fast to impress other people. We fast to build our self-mastery. Fasting is a means, but never an end. The benefits of fasting are innumerable, but all these benefits are secondary to the desire to embrace God more fully in our lives.
Source: https://www.dynamiccatholic.com/lent/catholic-fasting.html