Whether your skin will shrink depends somewhat on how you chose your parents (Genes).. some people's shrink and others not. Plastic surgeons make more money out of the latter group.
If you have stretch marks it is unlikely the skin will shrink back, as the basal collagen has been damaged. But regular fasting often helps it over time.
Now I believe in active fasting, and that's what I practice and administer. Just returned from a few miles hike/jog in our game reserve,(stirred up our antelope guarding their newborn) after more than 40 hours "on air", had some water.. . So that was followed by a kind of massage and sweat treatment and of course now the notion of food is not inviting at all.
I fast primarily to slow down the aging process. Losing weight can be a side effect in some people but the prime idea is to get healthier.. and when you are healthier, your weight tends to look after itself.