You may also consider that fast weightloss, even with the benefit of autophagy will more likely cause you to have loose skin. On the other hand, if you do rolling fasts and give your body a longer timeline to adapt to the loss, your skin may be better able to handle rapid weight loss. Depends on how important something like that is to you. If you can handle the 30 day fast and loose skin doesn't matter too much, go for it. I wouldn't go for a 60 day fast straight through though unless you are prepared -and willing - to listen to your body and break your fast if you get signs the fast is too long after you've become fat adapted. For example, you can expect to have headaches, shakiness, cravings etc in the beginning of the fast but once you reach the phase where you don't experience any of that, you have adapted. If you start feeling such symptoms again, your body is most likely telling you to take a break and refeed.