Here's a series of email replies that should also help answer your question.
http://forums.bible-truths.com/index.php/topic,11645.0.htmlThis is a passage concerning 'fasting' which is in all three synoptic gospels.
Mat 9:14 Then came to him the disciples of John, saying, Why do we and the Pharisees fast oft, but thy disciples fast not?
Mat 9:15 And Jesus said unto them, Can the children of the bridechamber mourn, as long as the bridegroom is with them? but the days will come, when the bridegroom shall be taken from them, and then shall they fast.
Mat 9:16 No man putteth a piece of new cloth unto an old garment, for that which is put in to fill it up taketh from the garment, and the rent is made worse.
Mat 9:17 Neither do men put new wine into old bottles: else the bottles break, and the wine runneth out, and the bottles perish: but they put new wine into new bottles, and both are preserved.
Some other statements from the Lord Jesus referring to fasting:
Mat 6:17 But thou, when thou fastest, anoint thine head, and wash thy face;
Mat 6:18 That thou appear not unto men to fast, but unto thy Father which is in secret: and thy Father, which seeth in secret, shall reward thee openly.
Mat 6:19 Lay not up for yourselves treasures upon earth, where moth and rust doth corrupt, and where thieves break through and steal:
Mat 6:20 But lay up for yourselves treasures in heaven, where neither moth nor rust doth corrupt, and where thieves do not break through nor steal:
Mat 6:21 For where your treasure is, there will your heart be also.
Luk 18:10 Two men went up into the temple to pray; the one a Pharisee, and the other a publican.
Luk 18:11 The Pharisee stood and prayed thus with himself, God, I thank thee, that I am not as other men are, extortioners, unjust, adulterers, or even as this publican.
Luk 18:12 I fast twice in the week, I give tithes of all that I possess.
Luk 18:13 And the publican, standing afar off, would not lift up so much as his eyes unto heaven, but smote upon his breast, saying, God be merciful to me a sinner.
Luk 18:14 I tell you, this man went down to his house justified rather than the other: for every one that exalteth himself shall be abased; and he that humbleth himself shall be exalted.
I get from Rene's post and the above that the WHY and the HOW/HOW NOT concerning fasting (in other words, the Spiritual) are the most important. Get those 'right' and I can do whatever I am led to do. That's far harder than it sounds. It's so much easier and comfortable and pleasurable to get reward now.