Loose skin is not just “skin”. Human skin is quite thin. It’s typically 0.5mm on your eyelids, and up to 4mm on your heels. If your “loose skin” is thicker than a few millimeters, it is merely covering what is underneath: flaps of fat and connective tissue.
The non-surgical approach to loose skin is to keep losing weight until your body fat percentage is below normal (below 12% for men; get a Bod Pod or DEXA scan), build more muscle, and consume skin-supportive nutrition. While your body may never erase the effects the disease of obesity inflicted upon your body, the remaining symptom of “loose fat” can slowly reduce over time.
The mechanism by which fasting – even intermittently – helps most is that it is more muscle-preserving than merely “eating less”. Secondarily, caloric restriction through fasting is proven to slow aging; younger bodies are more elastic and heal more quickly from the ravages of obesity.
Some brief, useful links: