How do Christians exercise self-control in the abstinence of food during fasting? I am aware of the Lord teaching us to pray, detailing how and how not it should be done, but the only thing he said about fasting was

"Moreover when ye fast, be not, as the hypocrites, of a sad countenance: for they disfigure their faces, that they may appear unto men to fast. Verily I say unto you, They have their reward.  But thou, when thou fastest, anoint thine head, and wash thy face; " (Matthew 6:16-17).

I do not recall where in the bible but I know faithful servants of God like David, Esther, Isaiah, Barnabas and Simeon fasted. We are even admonished to fast for  spiritual strength.

"Defraud ye not one the other, except it be with consent for a time, that ye may give yourselves to fasting and prayer; and come together again, that Satan tempt you not for your incontinency." (1 Corinthians 7:5).

How do christians carry out this exercise when food is very important for strength in the physical?

"If ye love me, keep my commandments. " (John 14:15).
How do Christians keep this very commandment?

Please if anyone could help me put this question in a better way to avoid closure, edits are welcomed
[Expecting @RiverC's answer among the responses as he inspired me to reask better.]
First, and foremost, fasting is a wonderful discipline which teaches you to subject your flesh to the desires of your heart.  It is an exercise in which you will struggle. The truth is is, our flesh may have been sacrificed (Rom 12:1) and crucified (Gal 2:20), but it is still with us! (Rom 7).

As an exercise, it is primarily an exercise in willpower.  It is the conscious decision, for a set period of time, to force your body to do what your mind and spirit know is best.  In way, it is much as Douglas Adams described flying -


  Flying is the art of attempting to hit the ground and missing!


In the case of fasting, it means that every time you are tempted to eat during the prescribed period, you take that thought captive (2 Cor 10:5), consciously decide to not act on the impulse, and instead turn to God. Fasting for more than a few hours means repeating this a lot.  In the same way that jumping jacks and pushups are hard work, so too is fasting!

For a more thorough treatment of the topic, the classic book on the subject is Richard Foster's Celebration of Discipline. He'll give many more practical applications of how to do this. (What to eat, what you'll your experience, how to deal with the hunger pains, etc...) 

As one example (and I forget if this Foster or someone else), your first 24-hour fast should be from lunch of day one, skip dinner, sleep (when you'll be most hungry), and skip breakfast. Eat a light lunch.  Also, be sure to drink lots and lots of water during the day.