If you try to fast to lose weight, you'll probably end up fasting for a few days at most; then you'll resort to eating less frequently to try to compensate for your unsuccessful attempt at complete fasting. This will actually make you gain weight.
But even if you successfully fast beyond several days and into weeks, you'll basically be killing yourself in a painful way. The lost weight will be in part from stuff you need to not die.
Losing weight is hard, but the first step is to stop denying that it's hard.