Some people say we(y.) must not have too much of a thing:
no hard work and no lazyness, no fasting and no overeating.
Some people say one can get good results on fasting only after 10 days.
So far I have done one day a week fasts. Now I can my day meals for 2. One is light and another one is very light. I also monitor my body weight and physical power. I want to keep it strong, but without access of the bodymass.
As for one day fasts - in the morning of a next day I did not feel like I want to eat any more. Also I tried shivambu fasting - this way I did not feel like I want to eat at all.
And I had better practice after fasting day on empty stomach.
I am not big fan of intence asana practice. One should egage and hold a posture as long as it feels right. I like to move slow in between.
So take it easy. If you don't feel like praticing - take a breake for 2-3 weeks and then start very easy and very slow. This way you don't hurt your body.