Say if you were 5'4" and weighed 170 lbs., spent 12 hours a day sleeping and the other 12 sitting in meetings, your calorie requirements just for those to things would be this:

Basal:1526
Activities:381
Total: 1907

With those numbers in mind, I cannot help but reply that 800 calories is dangerous. 800 calories is near starvation. Your body knows it needs the calories and will definitely tell you. Any sustained length of time is damaging and a not sustained length of time keeps you on the diet yo-yo.

Karen