I find while fasting I have trouble doing asanas at all. I'm a vata type and I lose weight and energy quickly. I would suggest do fewer sun salutations or standing asanas, except maybe something centering like the tree. I myself would try to focus on shoulderstand cycle, the bridge feels wonderful when you're a bit weak, forward bend and some backward bends. Of course, twisting will help you with elimination. Anything which opens your chest will give you a bit of energy. Fasting is a good time to focus on meditation and pranayama, reading scriptural or uplifting material and on nurturing yourself.
Maybe others will have more experience with fasting.