I haven't seen the documentary yet but discovered Kris Carr's Crazy Sexy Diet book. http://crazysexydiet.com/
She advocates a mostly raw vegan diet and having both juice and smoothies. Juice gives you a burst of energy; with smoothies you get the fiber and some protein etc. depending on what you add.
I'm not doing a fast but doing two meals a day of either green juice or smoothie.
I've only been doing it for a week and a half and I feel fantastic. Lost a few pounds and my exzema is gone.
There's a short cut to making juice btw; blend your green veggies, then push through a strainer! I have a juicer but in my tiny NY apartment setting it up and cleaning it is a hassle. This way I can have some juice and then put the fiber back in the blender with more greens and other stuff for a smoothie. I've also found that when using a juicer, unless you have a really powerful one, you can put the pulp back in after one pass and get more juice. Saves money.