Personally, there's no way I could sustain that. Shoot, I can't even get close to eating 1200 calories/day without feeling like I'm starving.
It's definitely true that the closer you get to goal the slower the pounds come off but I really believe this is something you have to accept and not go to drastic measures to bring it off. Sure, we'd all love to be at goal sooner but the time it takes to get there is a learning process. My journey as been long (over 1.5 years now and it could be another year for all I know until I reach goal) but it's given me time to change my habits and instill new ones. During that time I've become used to eating the way I do and I imagine it'll make maintenance significantly easier (I sure hope so!

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Certainly, some people can do well with quick weight loss but I would guess it would make figuring out maintenance more difficult because then you'd make a larger switch from low calories to maintenance calories. I've always kept my calorie deficit relatively low, which means maintenance for me will be pretty much what I'm already doing.
The 1200 calorie threshold is a tricky one. I think if your of average height or taller that it's a pretty good rule to go by (actually if you're physically active, young and tall I'd guess you need to even go a lot higher than that). However, if you're 5'0" tall, small framed, and pretty much inactive (for whatever reason), possible going under that would be acceptable. However, how sustainable that is... I have no clue.