"He maketh me to lie down in green pastures: He leadeth me beside the still waters." (Psalm 23:2)
There's a little room in a Benedictine monastery called a misericord. Though there's a double entendre to be had as that word also identifies a particular type of dagger that's used to kill a wounded opponent (the word literally means "act of pity, mercy, compassion, etc."). So keep in mind that this is a double-edged sword, of sorts.
The monastery misericord was (and still is in Eastern Orthodox denominations) used as a room in which a monk could lay down the duties of his ascetic, monastic vow and relax. Within, he could break his fast and eat meat. The act itself also bears the name misericord. Still another use for the word refers to a small seat on which parishioners sit during a service if they get tired. Same idea.
Now, the reason I bring all this up is because some people (myself included at times) have a hard time relaxing. They see God as an exacting and strict Father and not much else. Is God a God of judgment firstly? Or of love? What does this mean for us? (Hint: motive of heart plays in to the answer)
"Then came the word of the Lord of hosts unto me, saying, Speak unto all the people of the land, and to the priests, saying, When ye fasted...did ye at all fast unto me, even to me? And when ye did eat, and when ye did drink, did not ye eat for yourselves, and drink for yourselves?" (Zechariah 7:4-6)
Paul seems to answer directly to this problem of strict, loveless rulekeeping (and/or unabashed gluttony) when he says: "Whether therefore ye eat, or drink, or whatsoever ye do, do all to the glory of God." (1 Corinthians 10:31)
The Pharisees tried to criticize and condemn Jesus because His disciples didn't fast. Jesus answered them by citing the fact that it's hard to not celebrate (i.e. eat) while He was with them. (see Matthew 9:14-15)
When we adhere to a rule and forget the God who spoke, then the rule has no efficacy in our walking in the light as He is. This can be a hard thing to learn, because it requires that you rightly place the "knowledge of God" (Colossians 1:10) at the top of your to do list. And this isn't "knowledge" as in knowing about God. That's dry theology for you. Bereft of love, theology is worthless. No, this is "knowledge" as in knowing God. Admittedly, I don't fast much--not from food anyway. I ride a bicycle almost exclusively and it's unwise to not eat. My body would let me know. And it isn't that I get hungry, I'd likely get sick. It's not fun. So what do I do? Y'know, you can fast from things other than food? A good way to get to know God's voice better is to shut out other voices. Yes, your body has a voice and silencing and ignoring it by fasting and listening for the voice of God is the way to go. Fast from TV, from Social Networking (gasp!), even (dare I say it) from...(*whispering*) music. And don't let me tell you what or when or how. That's not my job. Relax. The Holy Spirit is the one who keeps you. And a fast is always--remember this--always for a good reason. It isn't just about "not doing something for no reason". It's about listening for the voice of God. And hearing Him clearer. Simple enough, right?
"He maketh peace in thy borders, and filleth thee with the finest of the wheat. (Psalm 147:14)
The other side of this: Jesus tells the Pharisees that "the days will come, when the bridegroom shall be taken from them, and then shall they fast." (Matthew 9:15) And as Jesus has both died and resurrected, effectively having been "taken from them", there are times and places for fasting. It behooves us to be as perceptive as possible to the slightest zephyr of the Holy Spirit. And relax.
"And take heed to yourselves, lest at any time your hearts be overcharged with surfeiting, and drunkenness, and cares of this life, and so that day come upon you unawares." (Luke 21:34) In other words, don't get so carried away with celebrating that you're not ready for the Second Coming. I mean that literally.
There's a fine line of moderation in doing things as unto the Lord. It's different for everyone. Listen for His voice and know that He loves you. He loves you the same, were you to disobey Him a thousand different ways a day, or obey Him perfectly for the rest of your days. It's not just what you do on the outside that tells. It's your heart motive. Why are you doing what you're doing? What you're not doing? And if He has you fast, you'll know it. Let Him know you're willing.
"And whatsoever ye do in word or deed, do all in the name of the Lord Jesus, giving thanks to God and the Father by Him." (Colossians 3:17)