Some prayers can only be answered if you pray AND fast:
Mat 17:16 And I brought him to thy disciples, and they could not cure him.
Mat 17:17 Then Jesus answered and said, O faithless and perverse generation, how long shall I be with you? how long shall I suffer you? bring him hither to me.
Mat 17:18 And Jesus rebuked the devil; and he departed out of him: and the child was cured from that very hour.
Mat 17:19 Then came the disciples to Jesus apart, and said, Why could not we cast him out?
Mat 17:20 And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.
Mat 17:21 Howbeit this kind goeth not out but by prayer and fasting.