I did it for a few weeks in prep for a hol. I lost 2 stone in the first 4 weeks (1Ib per day) but then plateau-ed!
I am happy to report that I suffered no side effect (but ffs DON'T drink on that diet).
After 48 hours on the diet, your body will have burned up all its glycogen stores (what carbs are converted into) and will then switch metabolic pathways and begin burning just fat.
You must not go more than 6 waking hours without eating, or you will mess up your metabolism. It's a good diet, but not a license to gorge.
Don't forget to keep an eye out for hidden sugars, even things like cough sweets are a no-no!