First off, Diabetics should take extra care if deciding to fast. If blood sugar levels drop too low due to lack of food intake, it can be very dangerous. This can also be bad (going without food) for people who work in strenuous jobs.
Say for example, If you work in the construction industry in an extremely physically demanding role. Like, you are digging, lifting, or using a full sized jackhammer all day, you definitely shouldn't be fasting. Someone working all day in a demanding role like that needs some food / energy throughout the day. Consuming nothing all day in a demanding role could make the person faint / pass out, and even cause an accident, either hurting themselves or someone else.
There is a calming effect after a while of not eating, but sometimes, no food can make people down right angry / irritated. I'm not big on fasting myself as I'm not overweight, but I know from my own experiences that when I haven't eaten anything all day I can sometimes feel quite irritated. Then, after getting something to eat, that feeling quickly dissipates and I feel good again.
If you are dead-set on long term fasting / water fasting I would say that for most people, no food at all isn't really the best way to go about things. Fair enough, you don't get to the Ketone stage talked about in the video, but you can still lose a lot of weight, if that's what you are personally considering fasting for. Some people do it for other reasons, such as healing. If you're doing it for healing then you would need to basically have nil-by-mouth for at least 3 days to get the healing / repair benefits.
However, short term fasting for weight loss can be very effective. I've seen the results in real life. Short term fasting, where you can eat a small amount of food each day, is much safer, and you can still lose a massive amount of weight in a short period of time.
