Dangerous? Perhaps not if done for a short time, provided you don't have issues that it aggravates.
Based on any sort of real, verifiable science? NOT AT ALL. Also, from Dr. Andrew Weil:
Quote:
...fasting and near-fasting routines such as the Master Cleanse are not effective weight loss tools - they alter your metabolism in a way that actually may make it harder for you to lose weight or easier to regain the weight once you go back to the way you normally eat. Most people compensate for the deprivation of the regimen by increasing their caloric consumption afterward.