Fasting basically makes your body start burning up your body
fat, after a 2-3 day metabolism adjustment period.
If you have been exposed to a lot of fat-soluble toxins
e.g. most insecticides, you can have significant to
severe health problems if they get dumped into your blood
stream faster than your body can detoxify them.
If you do it regularly, you won't have such an accumulation,
but if you haven't, be careful to watch for any signs listed
for exposure to common pesticides. If you get them, stop
fasting immediately and see a doctor specialising in
environmental illnesses if you can find one.
Really, it IS better to just switch to a healthy diet
that maintains your weight steady, and let your body
adjust at its own speed.