Recommended by the late, great Dr. Atkins as a way to overcome metabolic resistance to weight loss or to break a stall, a fat fast is simple: 1000 calories per day, 90% of those calories from fat.  Yes, this is calorie controlled as well as extremely low carbohydrate, and even low protein.  The fat fast catapults you into deep ketosis, with its triple benefit of appetite suppression, metabolic advantage, and protection of muscle mass.