Fasting means to abstain from something...not just food. The Bible mentions you should,not abstain from sex unless your spouse agrees or you open the door to troubles with Satan.
Some Bible verses on fasting.
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Acts 13:3
Then, when they had fasted and prayed and laid their hands on them, they sent them away.
Acts 14:23
When they had appointed elders for them in every church, having prayed with fasting, they commended them to the Lord in whom they had believed.
1 Corinthians 7:3-5
The husband must fulfill his duty to his wife, and likewise also the wife to her husband. The wife does not have authority over her own body, but the husband does; and likewise also the husband does not have authority over his own body, but the wife does. Stop depriving one another, except by agreement for a time, so that you may devote yourselves to prayer, and come together again so that Satan will not tempt you because of your lack of self-control.
Acts 13:2
While they were ministering to the Lord and fasting, the Holy Spirit said, "Set apart for Me Barnabas and Saul for the work to which I have called them."
Matthew 6:16-18
"Whenever you fast, do not put on a gloomy face as the hypocrites do, for they neglect their appearance so that they will be noticed by men when they are fasting Truly I say to you, they have their reward in full. "But you, when you fast, anoint your head and wash your face so that your fasting will not be noticed by men, but by your Father who is in secret; and your Father who sees what is done in secret will reward you.
Matthew 9:14-15
Then the disciples of John came to Him, asking, "Why do we and the Pharisees fast, but Your disciples do not fast?" And Jesus said to them, "The attendants of the bridegroom cannot mourn as long as the bridegroom is with them, can they? But the days will come when the bridegroom is taken away from them, and then they will fast.
Mark 2:18-20
John's disciples and the Pharisees were fasting; and they came and said to Him, "Why do John's disciples and the disciples of the Pharisees fast, but Your disciples do not fast?" And Jesus said to them, "While the bridegroom is with them, the attendants of the bridegroom cannot fast, can they? So long as they have the bridegroom with them, they cannot fast. "But the days will come when the bridegroom is taken away from them, and then they will fast in that day.
Luke 5:33-35
And they said to Him, "The disciples of John often fast and offer prayers, the disciples of the Pharisees also do the same, but Yours eat and drink." And Jesus said to them, "You cannot make the attendants of the bridegroom fast while the bridegroom is with them, can you? "But the days will come; and when the bridegroom is taken away from them, then they will fast in those days."