2010 I have done a 50 day fast, of which the first 20 days were water only and the last 30 days juice fast. On my juice fast I only consumed between 100 and 250 kcal/day and I mainly juiced fruit, cause I hate the taste of veggies. Fasting is a great way to break the cycle of binging/compulsive eating, if you have problems with this. After about 10 -14 days you are not constantly craving/thinking about food any more.
However, it is not a good method to lose weight. With a long fast you deplete your body of mineral and vitamins and your body uses up a lot of muscle as protein. In 70 days I lost 46 pounds and another 5 over the next couple of weeks but, probably due to malnourishment I started craving all kinds of foods and it sent me into a feeding frenzy and right back to where started, so I gained it all back and a bit extra.