Fasting is denying yourself. It is a sacrifice of nourishment for the brain and the body. Jesus calls us to deny ourselves for others. To put aside our desires and selfish motivation to help others. More importantly, we should not discuss fasting or seek pity from others. We're doing it to show God how sincere we are.
(Mark 8:34) then he called the crowd to him along with his disciples and said: "If anyone would come after me, he must deny himself and take up his cross and follow me.
We fast to show God that we are trying to establish discipline and sacrifice, to have our prayers answered, and to have God's righteous holy hand in our lives