I figured someone might be able to use some of this data. I have been a type 1 diabetic for 29 years (I'm 30). In the past year I have done 2 fasts: 1 was for 7 days no food, but did have juice on hand for any drastic drops in bg. The other was 2 days of 1 smoothie only, 2 days of only water, then 2 more days of 1 smoothie only. First off it can be done. I did it. I was alone when I did the water only and was with a roommate with the juice fast.
The first fast with juice was chaotic. I was on a pump and dropped my basal rates in 1/2, then three days in, in 1/4 of standard rates. It seemed to be working, but weird things would happen. I checked my bg every couple of hours or so. There was a particular time I felt clammy and anxious, so I figured I was low. Checked my bg and it was 223, which is just about where I wanted to keep it. But I felt terrible low, so 15 min later I checked again. It 47. This was no good. I drank some fresh squeezed carrot and orange juice. It went up shortly thereafter. The weird blood sugar sensitivity didn't leave for about 4 days after coming back to normal food. For instance, I went climbing 2 days after breaking the fast and my bg was at 250 and I had just eaten a can of pasta. Started climbing, bg plummetted. Went down to 40's. Ate two handfuls of glucose, came up to 150's, but plummetted again as soon as I started climbing. I literally had to stuff glucose tabs into my face all day and I couldn't keep it from dropping. So be aware if you choose to do this.
Fwiw, some miraculous things happened after this juice fast. I had arthritis in my big toes that was so bad that it caused vomitting on a couple of occasions. The doctors put me on IBprofin 800 mg and Voltarin, and the pain was was still so excrutiating that caused dizziness and vomitting. I couldn't move my big toes at all without pain. On the 6th day of this fast, I woke up to my toes wiggling without any pain, but still a little pressure. 7th day, pain free, and it's never really came back.
The second fast was in the early part of October this year. The 2 day smoothie part was to prime my body for the water only part. The smoothie days were pretty regular. The 2 day water only part actually turned out to be very enlightening. I was on MDI shots, with levimir as my long acting and novolog as my fast acting. I'm not a fan of pumps anymore, but thats another story. I stopped taking my long acting all together so I wouldn't bottom out. I actually got some really valuable data from this experiment. My blood sugar would raise 100mg/dl per 2 hours. Not 50 per hour, but 100 per two hours; as it was sometimes nothing the first hour, then 100, or 25, then 75, etc. This was with purely nothing in my system, no food, no anything.
It was kind of revealing to me, this trending upwards of 100 points every 2 hours IS Diabetes. That is what it is. I know that sounds kind of dumb, but this flux upwards (that I now have numbers for) is what it means to be diabetic. Anyways, I just treated the highs every two hours and my bgs were quite consitent (for once...). When I came back to foods, everything went back to normal. Back to my standard dose of levimir and novolog, and back to normal foods. As far as what I felt like during the fast, I felt horrible. Like I had the flu, but I don't think that had anything to do with my Diabetes. Anyways, i thought this might help a few people out there that are curious about fasting and diabetes.