My TDEE was 2.2k calories.
I would do 600 - 1000 cals. When doing them, I always eat the one meal at the end of the 48hrs at dinner to prevent eating another meal. It’s much easier to go into the next fast after dinner for me.
Also I thoroughly enjoy the mental benefits of being in a fastest state. So much so, it really got me out of a negative state of mind at the time. Similar to what exercise does.
I found eating 500 cals for that 1 meal made me feel weak, but that was probs mental.
I did this, and I lost 20kg in about 110 days. It’s worth it bro, I have abs now, and am now starting a lean bulk to get muscular.
I would also have 3-4 days at maintenance calories every 10 days or so. As a diet break, to restore myself, to then get back into it hard for the next 11 days.