I found something about sagging skin in this article by Herbert Shelton ,
"Weight loss may be secured without resulting in flabbiness or sagging of the skin and tissues. However, this is not true of elderly persons.",
he doesn't go into any further than that. The rest of the articles can be found here: http://www.rawfoodexplained.com/when-to-employ-fasting/pounds-that-slip-away....
I'm wondering about the same thing. I'm 30 and weigh about 230 lbs and want to lose 100. I guess I will just have to find out the hard way and keep my fingers crossed.