Based on my own experience and reading other peoples posts,for the diet to work you must set a target weight within the normal BMI range for your height and keep going until you reach it.Because Newcastle did it for 8 weeks the assumption seems to be that this is what it takes,however I think this will vary from person to person.
The diet was based on observations of bariatric patients,and the only one I know did not finally reach her base weight until nearly a year,at which time she weighed 10st 7lbs,down from somewhere north of 22 st!.
I took only 7 weeks to make my target of 12 st,however I had already used conventional exercise and diet to come down from 16.5st to 13.5st,so I was half way there before I started.