I did something very similar a couple times, a couple years back. I was trying to get to very low bodyfat levels. I was about 9% bf at about 215lbs, and I wanted to get to about 6 or 7%. For 21 days I drank a mixture of Met-RX Meal Replacement powder mixed 50:50 with Optimum Nutrition Protein powder. To this mixture I added a teaspoon of psyllium for fiber and a half teaspoon of flax oil for essential fats. About 2000 calories a day. After 21 agonizing days, my weight was down to about 205 pounds, however, according to a pinch test and the good old mirror, I lost mostly pure fat, as I had a very crisp line down the center of my abdominal region and my 4 pack became a crisp 6 pack. It's the leanest I've ever been. I want to point out that I was lifting heavy at the gym, and continue to do so. (been lifting consistantly for over 17 years now).
According to the various experimentation I've done over the years with protein, the best one-two punch for fat loss is the combination of protein and fiber. Without a significant amount of fiber, fat loss is not nearly as efficient. I normally get really lean for summer and then pack on the mass for winter, normally hovering around the 240 mark where I'm as strong as an ox at that bodyweight. Pretty radical diet. I don't recommend it. Better to throw in some solid meals.
I want to point out that if you try such a drastic diet with either too few calories or too much exercise, you will sacrafic muscle tissue. Once muscle tissue is sacraficed, metabolism is slowed down (about 1% per pound of muscle lost). Either take in adequate calories or reduce your workouts to 30 minutes. Trust me on this.