Hi shirleyh, Dr. Norman Walker in his classic book "Juice Fasting and Detoxification:" recommends at least one cleansing enema every day of a juice fast. It's what I do when fasting and I consider it to be an essential element of my fasts.
I don't think I could get through a day while fasting without an enema. If I have a headache, after an enema before even finishing on the toilet it's usually gone. It also helps to suppress hunger pangs and if I have a bad taste in my mouth the enema seems to eliminate that as well. I always feel better after an enema.
I also receive a colonic before starting a juice fast, and follow up a week or so after breaking my fast with another colonic.