That diet makes more sense. But, she was obviously not looking for something like that- I doubt she is a body builder trying to get a single digit body fat percentage.
I, however, am trying to get a single digit body fat percentage, so i'll give it a go and let you know how it works out.
By sustainable I mean general diet/exercise guidelines that a 'normal' person can follow like a healthy balance of carbs, protein AND fat and somewhat regular exercise. That's all anyone needs to get/keep healthy. The CKD stuff is for more dedicated/intense exercisers if you get what I mean.
telling someone something general like cut carbs and eat fat and protein like you did in the forum is going to send the wrong message because it is likely that they will not do the research and will do it wrong. That being said, I think this works if you have the dedication.