Many people think that juice fasting is hard or dangerous, but I can tell you that it's neither if it's done correctly. First, juice fasting is best done using vegetable juice. People go on a juice fast for many reasons - some to lose weight, some to detox, whatever. By using primarily vegetable juice, instead of fruit juice, you will get many more of the nutrients that your body needs. This includes macronutrients like protein, carbohydrates, and fat, but also micronutrients like vitamins A, B, C, D, E, K, and folic acid.
Vegetable juice contains far less calories than fruit juice, too, so if you're trying to lose weight, vegetable juice is a good way to reduce calories even further. You will, however, probably need to add a small amount of fresh apple juice to your vegetable juice to make it palatable, otherwise the juice can seem somewhat strong and sludgy. Carrot juice is good for this purpose also.
Second, people get wrapped up in the details of juice fasting, and you really don't need to. Just keep the juices centered on green leafy vegetables. Things like romaine lettuce, spinach, and kale should form the base for the juice, but veggies like asparagus, bok choy, and cabbage, work well, too. Beets, ginger, cucumber, and celery add extra flavor and nutrients.
People often ask, "Where will you get protein"? Or "Where will you get enough calcium"? Actually, it's very easy to meet your body's daily need for protein and calcium. A quick search online will reveal that leafy greens contain ample amounts of both protein, and calcium, along with all of the other necessary minerals. Additionally you will get the complete spectrum of proteins that your body needs.
Fresh juice made with a juicer is best, and the nutrients will pack the most potency, and the juice can be stored in the refrigerator up to a day. However if you cannot make fresh every meal, or every day, then you should freeze the juice immediately after making it to keep it as fresh as possible.
If you are juice fasting, there's no need to count calories, or even track the amount you are drinking. Every time you are hungry, just reach for a bottle of your fresh juice, and you should be fine - and as always, drink plenty of water.
Although juice fasting is very safe, any extended juice fast should be monitored by your doctor.