That is the pathway to failure. The body interprets that extreme dieting method as a semi-fasting mode. As such, the body slows down the metabolism and you'll have a hard time losing anything..Most people find it difficult to feel energized enough to get any exercise or concentrate with this method.
The analogy is to attempt to run a car without gasoline. The car will not operate for long before it won't start.
Using portion control and keeping dietary caloric intake to somewhere around 1100-1200 calories might help.
Furthermore, to chronically and drastically restrict your caloric intake may cause cardiac issues.