Consider this: When Our Father commanded Adam and Eve not to eat from the Tree of the Knowledge of Good and Evil, He was commanding them to fast. For fasting is not simply the disciplining of our flesh, but also submission to Our Lord's command. True obedience is true trust.
Yet Adam and Eve did not obey. Which means, they did not trust the Lord and submit to His Word. And that was shown in their refusal to fast. And by refusing to fast, they lost the Garden and all that He made for them.
So our first parents lost their way when they indulged their appetite and gratified their flesh. Had they only fasted from that tree as Our Lord commanded, they would not have run from Him in fear. Had they only fasted from that forbidden fruit, they would not have stood naked and ashamed before God and the world. Had they only fasted from the devilish enticement to live as they please, they would never have lived to die.
Perhaps this is why Jesus doesn't suggest we fast. He doesn't say, "Should you fast" or "If, perchance, you happen to fast" or "If you wish to fast." Instead, He says, "When you fast." And so Our Lord bids, commands and directs us to fast.
But which fast should we follow. Again, consider Adam and Eve. If their self-chosen diet led to our downfall, then it stands to reason that our self-chosen fasts will not lead us closer but further from the kingdom. And if that's the case, then perhaps this Lent we should not simply "give something up"--something that we've deemed worthy of sacrificing. Perhaps, instead, we should submit to the church's fast.
Now the church has many fasting traditions--even during Lent. And just as your doctor knows which prescription is best for you, an attentive caring priest or pastor or spiritual father should be able to prescribe a fast that is well-suited to your spiritual condition.
So here's the point--no self-chosen fasts this Lent. Rather, submit yourself to whatever fast you are given.
For you see, in the end, fasting really is simply a matter of submission and trust. And it is given by the Lord through His Church not as punishment or repayment, but so that you don't lose out the golden fruit of the Tree of Life.