RE: Nutritional Ketosis - you don't need (that much) fat!
I spent 16 weeks eating around 600 cals on a doctor supervised ketogenic diet. I lost 50 pounds and then kept it off eating high fat, low carb at around 2000 cals a day. I spent 8 weeks transitioning back to that level of calories. I don't believe my metabolism has been affected (any more than losing weight in any other way). the fact i have been able to keep the weight off for one year at a relatively high level of cals must be a good example of that.
What I will say tho is that there are some side effects of a very low cal diet - even if it is high in protein. One is a lowering of your blood pressure, a loss of salts and dehydration. I suggest keeping an eye on your blood pressure and taking a multivitamin - just in case. it is hard to get the nutrients you require on very low cal diets.
When the time comes to start eating more (when you reach the size/shape /weight you want) don't jump back in to normal low carb eating. be very controlled about adding calories back to you diet. Take a few weeks and keep the carb levels low throughout the process. it takes discipline - but i have to say that I found it easier than any other method of weight loss I have tried.'