Fasting hurts (the first one is really painful), demands prep, and I usually take time off when I do it. It only works with grahlin induced addiction. I will keep doing it because I have the habit now, but imho, on a macro perspective, openzic is better.
Because the injection is basically the only sustained weight loss mechanism that works on the population level. If a fast works for you knock yourself out. But fasts also come with risks like dehydration and malnourshiment.