According to experts, fasting isn't the most effective weight loss tool around. Joe Fuhrman, MD, who wrote Eat to Live: The Revolutionary Plan for Fast and Sustained Weight Loss and Fasting and Eating for Health, says that fasting can slow down your metabolic rate, meaning your diet from before the fast is actually even more fattening after your fast.
If you're healthy, a fast for a day or two might not pose any problems, but it could be a problem if your diet is presently unhealthy, or if you have liver or kidney complications, as well as a compromised immune system. Sometimes, fasts are accompanied by colon cleanses, which can be hazardous to your health, especially since you may be changing the bacterial balance of your intestinal tract and flushing out the good bacteria in addition to the bad.
I'm against anything radical myself unless it is under a doctor's supervision. I know that colon cleanses are over the counter but as you pointed out, if you have an underlying medical condition these can do more harm than good. Thanks for the great info.