Jesaiah:
Fasting basically serves 2 purposes. First, preparation for a work of ministry, second an act of self denial to make one more God Conscious. I
personally know of only 2 people who have fasted the total abstinence fast for 40 days. God asked that fast of these people as a preparation for ministry.
One does not have to keep a total abstinence fast to fast. The Daniel fast for example in which what you eat is strictly controlled.
Typically the Lenten fast is one in which you give up some aspect of your diet as an act of self denial. The most common example being the no meat on Fridays which is typically observed by catholics and orthodox alike.
Presently, I keep a weekly fast as part of my religious life. On Wednesdays we fast from solids from midnight til we eat a communal meal together usually around 6 PM. Its an act of obedience and self sacrifice designed to make us aware of how strong our flesh really is and to make us conscious of the Lord and his sacrifices.
We also keep seasonal fasts every Lent and Advent. This is a preparation fast - in which our meals are strictly limited almost like going on a diet!

AGAIN, the purpose being to make us more aware of God and of our own weaknesses.
Fasting on your own is easy. Fasting when some one esle tells you to fast or as part of a group - is harder. Satan works that much harder against you. He begins to tell you that so and so is not keeping their fast so why should you? OR - (I face this EVERY LENT!!) people just start offering you sweets out of no where! People who would not normally give you a glass of water if you were on fire, will offer you something you are not supposed to have during the lenten fast when you remove all sweets from your diet!