If you are asking because your health issues may cause some sort of painful or health-threatening reaction if you were to deny yourself food and water for an extended period of time, then I would advise caution. Nothing in this response should be construed as medical advice.

The physical act of fasting is also a spiritual exercise to focus our thoughts on the change of heart and mind that should be taking place within us.

Each person’s case is unique. Many who have forms of diabetes, or hypoglycemia, anemia, chemo etc. worry about the potential for fasting to cause them to pass out or end up in the doctor’s office.

If you are worried about fasting here are a couple of things you might want to try:

1. Experiment with a half day fast rather than a full day. This way you can gauge the effect fasting has on your system and make appropriate adjustments.

2. Allow yourself small sips of water so you can take essential medication.

3. When you do try fasting, keep a bottle of water handy along with some quick snacks so you are able to take them quickly if necessary.

4. Be careful about eating too fast or too much after your fast.

5. Ask God in prayer to help your body cope with fasting.

You may find that your body is able to handle a full day-long session of fasting better than you thought.

With that said, many health problems are not the sort that cause any concerns about the physical effect of fasting on the body. So let’s ask the question slightly differently:

Why might a person with health problems want to bother with fasting?

God has the power to heal us of our sicknesses and health problems. But God does not heal all people, of all things, in all places, at all times. Otherwise there would be no sickness.

First, He wants us to ask Him for His help. For our own good, our Creator wants us to recognize and acknowledge Him as life-giver, sustainer and healer.

Second, He wants us to submit ourselves to Him. A mindset of submission also means we are willing to accept His authority over our lives and accept whatever decision He makes regarding our request(s). This includes requests we make regarding our health.

The mindset of submission to Him in relation to healing and sickness is seen in James 5:14-16. People who are sick are instructed not only to pray, and seek prayer from others, but to present themselves to the elders in the Church to be anointed and prayed over.

Following these simple instructions is an outward expression of humble submission to the authority of God our Father—authority which He has also placed within His Church (Hebrews 13:17).

In the same manner, when we fast, we humble ourselves before God and submit ourselves to Him. Consider the words of Ezra: "I proclaimed a fast there, at the river Ahava, that we might humble ourselves before our God" (Ezra 8:21, English Standard Version). The physical act of fasting is also a spiritual exercise to focus our thoughts on the change of heart and mind that should be taking place within us. We submit our lives to Him. We obey His commands and instruction. We trust that He will always act upon our requests according to what is good and best for us.

Always remember: His overriding present desire is that you might come to understand and seek out that better resurrection available when Christ returns (Hebrews 11:35).

If we use fasting in this way—as a means to submit ourselves to God in humility, to request healing and relief from health problems—we can be confident that He hears and carefully considers our prayers. Yet if we are humbly subject to His authority over our lives, we will also accept His answer to our request(s) even if the answer is "no."

So fast, pray and make your requests known. Have faith that however God answers you He has made a deliberate choice as a loving Father. He's a Father who has your very best long-term interests in mind.