If fasting is something that is feasible, not injurious to your health, and you want to find out what it is all about, then begin slow and small. Obviously, forty days is not where to begin. Most of us find that fasting for a single meal, or maybe two, is the place to begin. Learn how your body reacts to not getting its usual amount of food. Also, fasting a meal or two is a realistic start. We are not setting ourselves up to fail, or to get so discouraged that we quit and miss out on the spiritual blessings of this discipline. Build a small base and then gradually increase the amount of time involved in the fast. Listen to your body along the way. If there seems to be some reason for physical concern, it is better to stop than put yourself at risk.
Perhaps, some might see all this as being too cautious. After all, is not life with Christ a matter of faith? Can He not be trusted to care for us if we go too far? What we need to remember is that we do not need to leave our head somewhere else when we seek to walk in a deeper way with Christ. Common sense is something given to us with the expectation that it will be used. While it may seem that all the expressed caution takes away from the Lenten invitation to fast, such is not the intent. Fasting is a spiritual discipline which can bring to us a deepened sense of God's presence which is a blessing we all seek.