If you can physically and mentally endure an 800 calorie diet in the long term, and can then transition successfully to maintenance, that's awesome.
Even in high school I couldn't do so without risking incredibly nasty symptoms. Severe IBS intestinal pain, diarrhea, dizziness, vertigo, blinding headaches, light headed weakness to the point that I would pass out (in college I passed out in a church confessional, talk about mortifying).
Interestingly on the Simple Diet, if you make your choices from the low end of the calorie guidelines for your 3 shakes, 2 entries, and 5 freggies, you will be eating only 705 calories per day.
I've been aiming for the middle range which averages about 1100 calories daily, and I've lost 19 lbs in a little over 3 weeks.