I fast for spiritual purposes. I know fasting is popular merely for the improvement of physical health. But I do not fast for health reasons. I have set fasting apart to be strictly a spiritual discipline. I hunger, seek, & strive to be more like my Savior. I want to better hear His voice, to be more keenly aware of how to serve this life for His purpose. I fast during my church's monthly unified fast for three consecutive days. I drink any liquid I want. That's my very simple fasting rule.
If you've done even basic research into fasting you'll know a person needs to be wise in the matter. Blood-sugar levels alone can cause a person to feel like they are hearing God and seeing angels. I breathe in every supernatural experience and keep it quiet. When my fast is complete and my body is regulated I revisit the experiences and determine which ones were of God, and which ones were a hormonal irregularity.
If you're allowing yourself to drink juice, the sugars and acids are going to be extra impacting to your system. I do not drink much fruit juices in general, but especially when I fast I limit them as it races my heart & makes me lightheaded. I drink "any liquid I want" solely for the purpose of functioning, not to fill my belly so I'm not hungry. I have children, co-workers and friends who are kind enough to put up with me and the affects of fasting. So I work extra hard on self-control of not just my appetite, but my emotional swings. I am easily annoyed & irritated when I fast, a natural result of altering the chemical changes in the body.
During my fast I detox my body. This is in no way a spiritual act to me. I do not detox in the name of God. It's simply "two birds with one stone." But here are the simple things I do to detox while I fast. I drink a lot of extra water, take shots of Apple Cider vinegar, and I take activated charcoal. (NOT the stuff you barbecue with.)
Again, you've got to exercise caution if you detox. I'm purposefully not writing how much I consume of each because I want you to get professional advice based on your own body's needs. You should tell your doctor so they can give you the proper guidance based on their knowledge of your health and medicines. For instance, activated charcoal is an absorption binder. It's purpose in detox is to absorb all the toxins in your body, bind them together, then eliminate them from your body. But it is no respecter of absorption, and that means it will absorb & bind your meds and nutrients as well as your toxins, eliminating the good stuff as well. You simply need to wait a couple of hours after a meal or meds to consume activated charcoal so that your body can benefit from the nutrients and chemicals. Your doctor will know what other precautions you should take if they know you're going to detox.
When I fast and detox I walk, and walk, and walk. Much of my job can be conducted on my mobile device, so I work and walk most of the day. In general I love to run. I don't like to run for long distances, but I love bursts of speed. But I do not allow myself to run when I'm fasting and detoxing. I have enough energy to do so. But it's not been smart for me over the course of several days. But I do walk a lot. Another physical thing that I do all of the time, but especially when I detox, is I sit in a sauna to sweat out even more toxins. Obviously, even more water is consumed during this process.
When I fast and detox I feel like I am on Cloud 9. I feel energetic. I feel happy. I love to fast & detox. If I didn't have a prescribed day to quit, I'd never eat again. I feel that great during a fast. The only downside I experience is my knowledge of the burden and annoyance I sometimes am to those closest to me. My energy is so high I flit & flitter all over the house, cleaning and organizing. My authority as mom and leader is more keenly felt as well, so I get quite bossy. The only down-side to fasting for me personally is that the self-control struggle is greater.
We all have our cross to bear, as we should since fasting is meant to be a spiritual metaphor of being crucified with Christ. For some it's headaches and hunger pangs. For me it's the effort of kindness and common courtesy so I don't lose friends and family.
As usual, I urge everyone to be in sync with your pastor and local community, while also understanding that they can't dictate, only encourage your private relationship with God. Church membership does not equal God-relationship. The church is a required supplement to your relationship with God, but cannot BE your relationship with God. Your pastor gives clear direction from the pulpit for the masses. But he or she doesn't go home with you and tell you step by step what to do or not do. Your ability to hear the Spirit of God is what guides you where you live. When it comes to your local church membership and pastoral authority you literally, "Can't live with it. Can't live without it."
Your pastor and local church may have a specific definition of "fasting." Therefore what I label as my "spiritual fast," may not be appropriate for you to label as yours. Nevertheless, this is my personal custom & discipline and perhaps it will motivate you. I hope you'll be inspired in your personal growth.