When juice fasting you will usually lose 1 pound or more a day(it doesn't always happen as soon as you start, sometimes it takes a few days until you notice weightloss). So if you had say 20 pounds to lose you should only fast for 20 days. If you went longer than that it could be very dangerous because your body will start feeding off your muscle or even your internal organs. When someone is nutritionally malnourished, which is the case with hair loss, fasting will usually cause more harm than good because your not getting the complete range of nutrients that you need, especially fat. Hair loss can be a sign of a fat deficiency. Try doing some research on the cause of hairloss and natural ways to treat it. If your heart is set on fasting don't go any more days than the number of how many pounds you need to lose and make sure your taking in whole food supplements and plenty of healthy sources of good fats, such as flax and hempseed oil. I would recommend you take bee pollen and spirulina throughout the day and also 3 tbsp. of flax or hempseed oil a day. After you complete your fast it would be good if you would eat a raw diet or high raw diet. Do some research on a raw diet, it can cure all health problems and reverse hair loss as well as help you to lose all your excess weight very quickly. To reverse your hair loss you going to need to eat lots and lots of leafy green vegetables and drink their juices as well. This will provide you with the proper minerals. And you will also need to eat lots of good fats, such as the ones in pumpkin, flax, and hempseeds as well as avocados. Good Luck