>>120739
He doesn't have loose skin because when you're fasting for an extended period of time, your body goes consumes proteins off your body to repair your muscle. It's phenomena called autophagy and it actually has a lot more health benefits than previously thought. As part of autophagy, the body generally understands that it doesn't require that excess skin as it continues to scrounge for additional protein for metabolic turn-over. Skin is fat and protein and water so it is a viable source. Dr. Fung can go into further detail regarding it and extended fasting itself.
As for 'gaining' all that weight back, it really is a question of lifestyle change. As you get closer to your target healthy weight, it would be unadvisable to continually go on 7+ extended days of fasting. While you're obese or very overweight, your body will burn about 90% fat and 10% of lean body mass due to turn-over on your metabolism. This is where the 'meme' of 'starvation mode' comes from, in that people assume that because of the 10% expenditure from lean body mass means that you're wasting away and losing all your gains. The reality is that as an overweight or obese person, you actually preserve more lean body mass than a traditional calorie restrictive diet. As for metabolism, this is again a meme. Increased energy expenditure and calorie restriction was the general advice that most people give. However it actually is more complex than that. Your insulin sensitivities and levels are what heavily determine everything from your metabolic rate to hunger levels. If you traditionally restrict calories, your body ramps insulin production. What ends up happening is spikes the release of ghrelin, which is the hormone associated with hunger pangs, alongside reducing your metabolic rate so you're burning less calories. This process does not stabilize either, and will continue as such until the person begins consuming a surplus amount of food once again. This is why diets, of all variety, have almost never resulted in permanent weight loss for their subjects, and the basal rate which you burn calories is very difficult to make up through increasing work.
Various fasting protocols operate on the same principles of keto. Carbs are converted into glycogen by the liver, and is used as fuel for your body (glycigenisis). Glycogen is your body's immediate fuel source, while Ketones (fat) are what it stores for emergency use. By limiting (20-50g) or removing the access to carbs, your body does not have glycogen to carry out its processes, so it has to begin using ketones as energy. Ketogenesis (not be confused with ketoacidosis) is when your body is using ketones as its primary source of fuel. This process can be an annoyance when you first go through it, and often you have symptoms that are dubbed 'Keto Flu'. These symptoms will pass within a couple days to a week, depending on if you're eating keto or fasting (fasting is much quicker given how you are denying your body any access to carbs as opposed to a limited amount). Ketones are important because they lower your insulin levels and over time, increase your sensitivity to it. Like a domino effect, this also limits the production of grehlin which is also important because it limits your hunger. My personal experience, along with what I read, is there is generally a two day hump before your hunger levels stave off. Now this isn't an easy process and it takes work, but I think I've made a case for its viability for weightloss.
Of course you need to speak to your physician, but it generally is inadvisable if you have:
>Medication that require food
>existing health conditions
However with that being said, there are surprising levels of work arounds to those issues, after speaking to a physician who is familiar with fasting protocols.
TLDR: Fasting has been pretty effective for me and the science behind it is sound, it's just rough for the first couple days, and there are a lot of flexible ways to approach it as opposed to the hard fast.
Here is a video that can explain this in detail
https://www.youtube.com/watch?v=tIuj-oMN-Fk