Many Christians have some unhealthy opinions about religious fasting. Many of them believe that fasting allows them to earn an extra degree of holiness. However, you cannot in anyway pay for your sins by fasting.
Also, some Christians believe that God commands them to follow certain religious fasts, such as lent. This is not true. No Christian is commanded to to undergo a ritualistic fast:
Since you died with Christ to the elemental spiritual forces of this world, why, as though you still belonged to the world, do you submit to its rules: 21 “Do not handle! Do not taste! Do not touch!”? (Colossians 2:20-21 NIV)
These rules that tell us we have to deprive our physical body in order to make God happy were not made by God. These rules, such as the Lenten fasts, were created by men:
These rules, which have to do with things that are all destined to perish with use, are based on merely human commands and teachings. (Colossians 2:22)
As a Christian you have no obligation to follow these fasts. These fasts do not make you righteous in the sight of God, since you are already righteous in the sight of God if you have believed in Jesus Christ for salvation:
know that a person is not justified by the works of the law, but by faith in Jesus Christ. So we, too, have put our faith in Christ Jesus that we may be justified by faith in Christ and not by the works of the law, because by the works of the law no one will be justified. (Galatians 2:16)
Does this mean that a person should never fast? No! You may fast as long as you do not trust in your fasting to save you or pay for your sins. It is perfectly alright to fast for lent if you do it with the right motivations. Fasting can be part of a prayerful time of reflection when we seek to learn from God what He wants us to do. It can be a way for us to show God privately that we are serious about loving Him and seeking His will. Indeed, most fasting should be done privately. Jesus commanded that fasting should not be done for show.
“When you fast, do not look somber as the hypocrites do, for they disfigure their faces to show others they are fasting. Truly I tell you, they have received their reward in full. 17 But when you fast, put oil on your head and wash your face, 18 so that it will not be obvious to others that you are fasting, but only to your Father, who is unseen; and your Father, who sees what is done in secret, will reward you (Matthew 6:16-18).
Fasting should never be done to make you look more holy to other people. Never fast in a way as to deliberately force other people to acknowledge the fact that you are fasting. Rather, conduct your fasts in a quiet and reserved manner. Sometimes people will notice that you are fasting; this is OK, but do not lobby for their attention.