I’m thinking about trying Optifast for awhile, but don’t want to totally destroy my metabolism and increase the (always substantial) odds of a fast weight regain by making my body go into starvation mode and start conserving calories. Does anybody know (with cites, if possible) how long on average a person can maintain a very low calorie regimen before their body catches on and slows their metabolism to a crawl? My hope is to do Optifast long enough to get a head start on dieting, then switch to something not quite as brutal before my metabolism is too badly screwed.
For the record, I am morbidly obese and am painfully aware that any substantial weight loss will decrease the calories it takes to maintain my body, thus necessitating a lower calorie intake to keep on losing. I am also aware that exercise helps keep metabolism up. I am not asking about the effects of a lower body weight, I am asking about the body’s response to starvation.
Please note that the question I am posing relates to metabolism and is not a request for critiques of Optifast in particular or dieting in general.
Thanks for your help. 
I probably won’t check back for answers till the morning.