Second point – no there is no way around this, ‘easing back’ you will still put on a disproportionate amount of fat, due to the loss in muscle, and decrease in metabolism. Also your body releases a hormone called leptin when you are effectively starving on a crash diet, and this makes your body ‘suck’ up any fat you eat and store it more effectively.
References :
People who crash diet ALWAYS end up fatter. I’ve seen it with my own eyes.

I know that crash diets (dramatically reducing food intake in order to lose weight quickly) are regarded as unhealthy, and from what I’ve gathered, this is for two reasons:
(1) You can’t possibly get all of the nutrients your body requires on only 500-1000 calories per day.
(2) Eating little slows down your metabolism; thus, when you start eating more again, you will rapidly gain the weight you lost back.

Fact 1 can’t be counteracted, but I would argue that the average person does not consume an ideal quantity of nutrients in the first place. What if the dieter, by watching his or her diet, actually *increases* his or her daily intake of vitamins, minerals, etc., even while consuming fewer calories than what he or she was previously used to, by choosing healthful meals and eliminating the "empty calories" that he or she previously gained from unhealthy meals?

My main question is about fact 2. When researching how unhealthy fad diets were, the prevailing argument seemed to be, "Once you start eating normally again, you’ll gain all the weight back." But couldn’t you avoid that by easing back into a healthy intake of calories (say, 1800/day whereas you were consuming 500-1000/day during your diet) gradually? Especially if you couple this with increasing exercise, it seems that you would actually *benefit* your metabolic rate in so doing.

Does anyone have any evidence to the contrary, or any input at all?
crash diets, not fad diets*