My thoughts on fasting are, I think it is beneficial in intermittent short periods. I think in today's day and age due to the massive amounts of toxins we have in storage, it can be very damaging to try and detox very quickly. It can be deadly in fact due to the quick release of toxins and the body's inability to deal with the toxins released from safe storage.
I prefer a nutritional raw foods approach that supplies optimal nutrition and allows the body to detox stored toxins at a much safer rate.
I also think that many people use severe fasting approaches for unhealthy weight lost based on trying to achieve a quick fix. A better approach would be to shore up self esteem issues and then realign their lifestyle to a raw living foods approach with exercise included.