This is going to be a ridiculous question but...?!

You don't become ALL skin and bone. I think you are just misunderstanding generalized statements and human anatomy.

There is ALOT of muscle wasting (atrophy) in anorexics,.. and the body must have a source of fuel at all times.. so the majority of fat is eaten for food.

What is left?

Someone who looks very feeble, malnourished, and like there is just skin and bone.

When in fact they have ALL the muscles they were born with. These muscles are just incredibly weak, and very thin from the body using them as fuel. While the body literally eats itself (everyones) for fuel.. it turns to more muscle than in most people in anorexics because the fat stores are used up for obvious reasons. However, the body won't eat ALL of our muscle. It won't eat a muscle so much that it is cut in half, or is no longer functional.

So , in other words, if you were to cut the skin off an anorexic, you would see all the typical muscle anatomy of a normal person, just alot thinner , less dense, and smaller.

If it was just skin and bones, the person wouldn't be able to move, breath, etc.

The body still holds onto some fat when anorexic.. even the 'perfect' picture of anorexia has fat. It is just hard to distinguish. We also have lots of internal fat surrounding our organs (which is essential as well). In anorexics this is eaten as well and creates a different set of dangerous health conditions.

There is no mystery here,.. it is just a much accelerated/advanced process that happens to anyone whom you see 'fast', or go on a severe crash diet. Given long enough you look a certain way.

Finally, just to put this out there -- many anorexics don't have the typical 'stick figure' look.

Once you've not eaten for such a long time than your body starts to feed off the fat. It eats it and it starts to eat your muscle too because it's so hungry.

You might already have an eating disorder.