Sounds like Dr. Atkins' Fat Fast. You'd have to do it w/5 servings macadamia nuts, though. That plan basically is for a 3 day use when you've stalled after a few weeks on his diet. For 3 days, you eat 1000kcal, with almost all cals from fat.
He had studies showing 2 groups who used 1000kcal diets for a few weeks (2 or 3, can't remember) and the results were something this: The fat fast group lost 15lbs, 14.5 lbs. fat. The higher carb group lost around the same, but only lost 7 lbs fat (that's a guess, it was low, but I can't remember).
Basically, what I hear, is that by giving your body only fat to work with, it hordes any aminos it can get and uses fat for every function. Not sure how it would work on more active people, though.
Where did you hear about the 6 servings/water plan J?